J. c,in. Path. (1957), 10, 236. STUDIES ON CONCURRENT SENSITIZATION AND TRYP- SINIZATION WITH THE DEVELOPMENT OF A SIMPLE TRYPSIN TUBE TEST FOR ROUTINE RHESUS GROUPING AND AS A SCREENING TEST FOR INCOMPLETE ANTIBODIES BY N. A. F. YOUNG From St. Margaret's Hospital, Epping, Essex (RECEIVED FOR PUBLICATION MARCH 26, 1957) In their original publication Morton and Pickles (1947) described the use of trypsin for the detection of incomplete anti-Rh antibodies. They found that it caused cells sensitized with an incomplete antibody to agglutinate, and also that it enhanced the specific agglutination of other haemagglutinins in the absence of any detectable antibody of the incom- plete type. Preliminary trypsinization of test cells followed by their incubation with sera containing incomplete antibodies proved highly sensitive and specific, saline suspensions of such "trypsin- treated cells " being readily agglutinated by incom- plete antibodies. They mention that when trypsin was added to the serum-cell mixture, i.e., concurrent action of enzyme and antibody, its action was inhibited by the natural trypsin inhibitor present in all sera (Delezenne and Pozerski, 1903). This effect could, however, be overcome by the addition of excess enzyme. Subsequently, in the Journal of Clinical Pathology (Morton and Pickles, 1951), the same two authors give details of the development and standardization of their proteolytic enzyme test, and follow this with an assessment of its value in the light of their experience gained during a two-year trial study. Their procedure of preliminary trypsinization with subsequent sensitization has remained as the stan- dard method for the performance of the trypsin test. They found that it gave reliable results and was more sensitive than either the albumin or anti- human globulin methods in the detection of weak anti-D antibodies, and they concluded that: " The ease of interpretation, and the clear-cut results obtained when the results of other tests are equivocal, have led us to use the P.E. test as the final arbiter as to whether anti-D antibodies are present or not." It is therefore surprising to find that this highly sensitive and reliable test does not seem to have gained the popularity it merits, nor to have come into general use in a number of pathological departments where routine blood grouping and antenatal supervision are carried out. This means that undue reliance is placed upon the Coombs A.H.G. test to define weak sensitization, and it is well recognized that this reagent is notoriously temperamental and liable to sudden unexpected deterioration in potency. Furthermore, in the study of antibodies other than anti-Rh, it has been frequently demonstrated that the results of the Coombs and trypsin tests, while agreeing in the majority, do not strictly parallel one another. For this reason, as recommended by Dacie (1954), these two tests should be considered as complementary to, and not as substitutes for, one another. This applies particularly to haemolytic conditions of warm or cold auto-antibody types, in which the enzyme test is extremely sensitive and may detect an antibody when the results of other tests are negative. For indirect testing corresponding to the indirect Coombs test the accepted trypsin technique is convenient, since the requisite test cells can be trypsinized in bulk, and then used for checking all the sera to be tested. It does, however, involve two separate incubation periods. For the testing of a variety of unknown cells against a known incomplete serum such as albumin anti-D, or for checking the reactions of an unknown antibody against a battery of cells of known geno- types, the standard trypsin test is time-consuming, because it involves the preliminary trypsinization of the individual groups of cells to be tested. on 22 May 2018 by guest. Protected by copyright. http://jcp.bmj.com/ J Clin Pathol: first published as 10.1136/jcp.10.3.236 on 1 August 1957. Downloaded from
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J. c,in. Path. (1957), 10, 236.
STUDIES ON CONCURRENT SENSITIZATION AND TRYP-SINIZATION WITH THE DEVELOPMENT OF A SIMPLE
TRYPSIN TUBE TEST FOR ROUTINE RHESUSGROUPING AND AS A SCREENING TEST
FOR INCOMPLETE ANTIBODIESBY
N. A. F. YOUNGFrom St. Margaret's Hospital, Epping, Essex
(RECEIVED FOR PUBLICATION MARCH 26, 1957)
In their original publication Morton and Pickles(1947) described the use of trypsin for the detectionof incomplete anti-Rh antibodies. They found thatit caused cells sensitized with an incomplete antibodyto agglutinate, and also that it enhanced the specificagglutination of other haemagglutinins in theabsence of any detectable antibody of the incom-plete type. Preliminary trypsinization of test cellsfollowed by their incubation with sera containingincomplete antibodies proved highly sensitive andspecific, saline suspensions of such "trypsin-treated cells " being readily agglutinated by incom-plete antibodies. They mention that when trypsinwas added to the serum-cell mixture, i.e., concurrentaction of enzyme and antibody, its action wasinhibited by the natural trypsin inhibitor present inall sera (Delezenne and Pozerski, 1903). This effectcould, however, be overcome by the addition ofexcess enzyme.
Subsequently, in the Journal of Clinical Pathology(Morton and Pickles, 1951), the same two authorsgive details of the development and standardizationof their proteolytic enzyme test, and follow thiswith an assessment of its value in the light of theirexperience gained during a two-year trial study.Their procedure of preliminary trypsinization withsubsequent sensitization has remained as the stan-dard method for the performance of the trypsintest. They found that it gave reliable results andwas more sensitive than either the albumin or anti-human globulin methods in the detection of weakanti-D antibodies, and they concluded that: " Theease of interpretation, and the clear-cut resultsobtainedwhen the results ofother tests are equivocal,have led us to use the P.E. test as the final arbiteras to whether anti-D antibodies are present or not."
It is therefore surprising to find that this highlysensitive and reliable test does not seem to havegained the popularity it merits, nor to have comeinto general use in a number of pathologicaldepartments where routine blood grouping andantenatal supervision are carried out. This meansthat undue reliance is placed upon the CoombsA.H.G. test to define weak sensitization, and it iswell recognized that this reagent is notoriouslytemperamental and liable to sudden unexpecteddeterioration in potency. Furthermore, in thestudy of antibodies other than anti-Rh, it has beenfrequently demonstrated that the results of theCoombs and trypsin tests, while agreeing in themajority, do not strictly parallel one another. Forthis reason, as recommended by Dacie (1954), thesetwo tests should be considered as complementary to,and not as substitutes for, one another. Thisapplies particularly to haemolytic conditions ofwarm or cold auto-antibody types, in which theenzyme test is extremely sensitive and may detectan antibody when the results of other tests arenegative.For indirect testing corresponding to the indirect
Coombs test the accepted trypsin technique isconvenient, since the requisite test cells can betrypsinized in bulk, and then used for checking allthe sera to be tested. It does, however, involve twoseparate incubation periods.For the testing of a variety of unknown cells
against a known incomplete serum such as albuminanti-D, or for checking the reactions of an unknownantibody against a battery of cells of known geno-types, the standard trypsin test is time-consuming,because it involves the preliminary trypsinizationof the individual groups of cells to be tested.
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STUDIES ON CONCURRENT SENSITIZATION AND TRYPS1NIZATION
Potent " albumin agglutinating sera " are muchmore prevalent than " saline " ones, and certainlymore readily obtainable overseas, and it was thisfact which originally led to the investigation ofthe possibility of modifying the usual trypsinprocedure in order to make it quicker and moreconvenient, thus widening the field of its routineapplication.As the result of experimental studies, two methods
have been evolved which are simple and easy toperform, involving the minimum of manipulations,and giving highly sensitive and reliable results. Inthe first, referred to as the " trypsin-saline test,"the trypsin agglutination reaction takes place in asaline medium. In the second, referred to as the" trypsin-albumin-plasma test " increased sensitivityis obtained by allowing the reaction to proceed in aprotein medium.
These two tests have proved themselves to be assensitive and as reliable as the standard trypsin test,and their adaptation to routine clinical studies withan evaluation of their uses will be given later,together with the results obtained during a trialperiod when they were compared with othermethods.
Materials and Methods(1) Crystallized trypsin (Armour Laboratories).(2) N,20 HCI. Concentrated HCI, sp. gr. 1.18,
0.85 ml., is dissolved in 200 ml. distilled water.
(3) pH 7.7 phosphate buffer.
A. Na2HPO4.12H20B. NaH2PO4.2H20
.. 4.11 g. %
.. 2.34g.0%For use, 90.5 parts ofA are mixed with 9.5 parts of B.
The mixture keeps well for weeks at bench temperature.
(4) Albumin-plasma Mixture. Four parts oxalatedplasma and 1 part 20% bovine albumin are required anddiluted 1: 1 with saline for use.
(5) Stock Trypsin Solution. A 3% solution is made bydissolving 300 mg. of the crystallized trypsin in 10 ml.N120 HCI. This keeps well for four to six weeks storedin the refrigerator.
If the mixture of trypsin and buffer solution is madewhile the trypsin solution is still cold, turbidity due toprecipitation of phosphates occurs. This redissolves asthe mixture warms up and can be hastened by placingthe solution in a water bath. This latter is not imperativesince the use of the solution while still turbid does notappear to interfere with the agglutination reaction.
(6) Test Trypsin Solution. This is prepared freshlyeach day from the stock using the phosphate buffersolution as diluent. The optimal strength for the testswas found to be 1.2%, giving a final trypsin concentra-tion of 0.48% in the serum -cell mixture with the tech-niques used.
A capillary constant-drop pipette is used for measuringvolumes.Red cells used in tests are washed twice in saline and
made up to approximate 10% saline suspensions.All tests and controls are set up in 3 x 3 in. rimless
test-tubes and incubated in metal racks in a water-bathat 370 C. for two hours.The following have been used and will be further
discussed in this paper:
Routine Rhesus Grouping.-The sensitivity of thistest is such that an albumin anti-D grouping serum with atrypsin titre not less than 1: 64 may be used diluted 1: 10in saline for detection of all D + bloods (see reference toDu bloods later). Two volumes diluted anti-D serum areplaced into a tube with 1 vol. of 10% suspension of redcells to be tested, and 2 vol. 1.20% trypsin is added.
Routine Antibody Screening Test for Antenatal Cases.Two volumes of each serum for test are placed in a tube,with 1 vol. of the appropriate test cells (R1R_ R 1r, rr, etc.)and 2 vol. of 1.20% trypsin added to all tubes.
Titration of Incomplete Antibody.-Titrations areperformed in saline and albumin-plasma media. Doub-ling serial dilutions of the serum for test are made insaline and albumin-plasma mixture. Two volumes ofeach serial dilution are placed in separate tubes and toeach are added 1 vol. of the appropriate test red cellsuspension and 2 vol. of 1.20' trypsin.
Detection of Red Cell Sensitization (Direct TrypsinReaction).-The cells to be tested are washed threetimes in saline and made up to a 10% suspension.Two tests can be performed, the second giving increasedsensitivity.
Trypsin-salinie.-One volume of the cell suspension isplaced in a tube, 2 vol. of saline added and then 2 vol.of 1.2% trypsin.
Tr)psin-alburnin-plasnia.-One volume cell suspensionis placed in a tube, 2 vol. albumin-plasma mixture isadded, and the 2 vol. 1.2% trypsin.
Macroscopic and microscopic readings are taken aftertwo hours' incubation. The final readings are madewithout centrifuging by gently tapping the tubes toresuspend the sedimented red cells. Agglutinationshave been recorded as: 4=solid clump of cells, 3=afew large clumps, 2= fairly numerous medium-sizedclumps, 1=scattered fine agglutinates, and M=micro-scopic readings graded by plus signs.
Detection of Incomplete Antibodies in SeraIt was realized that at least two factors would need
consideration. In the first place, since it seemed likelythat the optimal incubation time would lie betweenone and two hours, it was feared that this mightresult in non-specific agglutination due to over-trypsinization should the final concentration oftrypsin in the serum-cell mixture necessary forsatisfactory agglutination prove to be high.
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Secondly, the presence of trypsin inhibitor in normalsera meant that an increased concentration oftrypsin would be needed, and furthermore it wasthought that a critical concentration might provenececsary in order to achieve maximum sensitivity.
Relationship between Trypsin Concentration andNon-specific Agglutination by Normal Sera.-Usingthe standard trypsin test, there are optimal con-ditions for the trypsin modification of the test cells,and the strength of the trypsin solution is important.When used in weak concentrations it modifies thered cells so that they are specifically agglutinated bysaline dilutions of homologous antibodies. How-ever, as shown by Wheeler, Luhby, and Scholl(1950), when used in progressively higher concen-trations the red cells are altered so as to becomeagglutinable by most normal sera and finally bysaline. They demonstrated that from 0.4% upwardsnon-specific effects occurred in most sera, and at aconcentration of 1.6% the red cells agglutinatedeven in normal saline.With the " concurrent method " using the tech-
niques given in which the minimal serum dilution is1: 2.5, this non-specific reaction does not presentany difficulties provided the readings are madewithout centrifuging, and it has not occurred in themany sera tested using a wide range of final trypsinconcentrations from 0.23 to 0.72%. If the tubes arecentrifuged the positives are markedly accentuated,but associated with this in many cases there alsoresults a fine diffuse " cayenne-pepper type "agglutinate of non-specific character in a number ofthe previously negative tubes. This should not leadto error, since it needs little experience to differen-tiate it from true agglutination. The agglutinate isvery easily dispersed by tapping the tube, andwashing twice in saline causes these false agglu-tinates to disperse, whereas true agglutinationpersists, and in most cases is more distinct. Thisreaction would appear to depend upon " stickiness "of the red cells causing them to adhere under theinfluence of centrifugal force in the presence ofserum. As distinct from this reaction, an occasionalantenatal serum will give a clear-cut agglutinationif centrifuged after incubation. This disappearswhen the tube is replaced in the water-bath, and isdue to the presence of incomplete cold antibodywhich can be shown to occur in higher titre thannormal and active over a wider thermal amplitudein a few cases during pregnancy.
Influence of Trypsin Concentration on SpecificIso-agglutination in Antigen-antibody Mixtures.With final trypsin concentrations ranging from0.033 to 0.08% the inhibitory effect of serum was
evident. There was complete blocking with absenceof agglutination at 0.033%, and this was followedby a progressively lessening blocking effect as thetrypsin strength was increased, although even at0.08% agglutination was still absent when the serumdilution was less than 1: 8. Moreover, the agglu-tinates were weak and only microscopic, and thetitre of the serum very low compared with othermethods.
Further tests were made with considerablyhigher trypsin concentrations, using strong andweak albumin anti-D sera and Group 0 Rjr and Jrcells. The results as shown in Tables I and Ir
TABLE IINCOMPLETE ANTI-D FINAL TITRE 1: 256 BY STANDARD
TABLE I IWEAK INCOMPLETE ANTI-D FINAL TITRE 1: 4 BY
STANDARD TRYPSIN TEST
Final Trypsin Final Serum DilutionsConcentration (%) 1/2-5 115 1/10
020 - - -
0-24 M+ + _0-32 I M+ -
0-40 1 Mi+ + -
0-48 1 M+-+ -
0 56 I M++ -
0.60 M+++ Mi0-72 M +++ _
indicate that there is an optimal trypsin concen-tration which ranges between 0.40 and 0.56%.Within this range, the test is sensitive and specific,giving clear-cut reasily read agglutinates. Readingstaken at one hour were the same, but were notquite so clearly defined as at two hours. Repetitivetests on a number of different sera have proved itsreliability and reproducibility of these results.The enhancement effect of albumin-plasma
mixture was studied. Titrations were made of in-complete anti-D sera serially diluted in saline andalbumin-plasma, and the results compared withthose obtained by the standard trypsin and Coombsmethods (Table Ill). It is apparent that the " con-current method" gives as clear-cut results as the
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standard trypsin method, and to as high a titre.There is no marked enhancement by albumin-plasma when the antibody is strong, although itdoes produce a definite increase in sensitivity whenthe antibody is weak. It seems to be of moreimportance for the trypsin agglutination reactionwhen the cells are sensitized first and sub equentlytrypsinized (Table M).
The Detection of Red Cell SensitizationFor the detection of " sensitized red cells," it was
thought possible that the critical concentration oftrypsin might have to be increased in order that cellsalready coated with antibody should agglutinatemaximally, because it was felt that, if the action oftrypsin were to modify the surface of the red cell,this might well be impeded by the previous " coat-ing."
In view of the fact that sensitized cells willagglutinate when suspended in an albumin-plasmaor albumin-serum mixture, and also that theirtrypsin agglutination reaction in albumin-plasma isextremely sensitive-even more so than the anti-human globulin reaction-as shown by Dausset(1952), the effects of plasma, serum, immune humangamma globulin, bovine albunin, and plasma andserum-albumin mixtures, were studied as well asthose obtained by trypsin-saline.
Influence of Trypsin Concentration on Agglutina-tion of Sensitized Red Cells in Trypsin-saline andTrypsin Albumin-plasma.-Primary union betweenantibody and red cell does not affect subsequenttrypsin action, and the optimal trypsin concentra-tion remains in the 0.40 to 0.60% range. However,the importance of a colloid factor in the trypsinagglutination mechanism is clearly demonstratedby the greatly increased sensitivity of the trypsin-albumin-plasma as compared with the trypsin-saline method. Moreover, its greater sensitivitythan the Coombs is also apparent and it gives afour-fold increase in titre over this method (TableIV). The potentiating factor does not reside in
bovine albumin, for the agglutinations obtainedusing this instead of albumin-plasma mixture areno stronger than those of the trypsin-saline test.Fresh plasma and serum are equally efficacious,nor is the factor thermolabile since heat inactivationdoes not impair their enhancing effect. Serumwhich had been stored for a number of months wasineffective. Immune human gamma globulin serumproduced good enhancement of the trypsin agglu-tination which suggests the possibility that thefactor may reside in the gamma globulin fraction.It would be interesting to learn whether plasmafrom a case of agammaglobulinaemia would bewithout effect.The agglutination of sensitized cells in varying
concentrations of albumin-plasma without trypsinis much less marked, and it can be shown that theamount of albumin-plasma required for the clump-ing of such cells is in reverse ratio to the degree ofsensitization (Dausset, 1952).
TABLE IVINFLUENCE OF TRYPSIN CONCENTRATION ONAGGLUTINATION OF SENSITIZED RED CELLS
FinalTrypsin Red Cells Coated with Decreasing Amounts of Anti-DConcen-
Nature of the Trypsin-Agglutination MechanismAbsorption experiments have shown that " tryp-
sinized cells'" absorb more incomplete anti-D thanfresh cells, and that this absorptive capacity can beincreased (up to a certain point) when greateramounts of enzyme are used in the preliminarytrypsinization (Hubinnot, 1951). Wheeler, Luhby,and Scholl (1950) have confirmed this increasedabsorptive capacity of " trypsinized cells."The absorption of antibody is specific inasmuch
as only those cells which contain the homologousantigen can absorb it, and that this absorption mustpresumably take place at specific haemagglutinogenloci on the red cell. It would thus seem reasonableto conclude that the action of trypsin is to increase
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the reactivity of these loci, and its action is thereforefocal and not, as has been suggested, a generalizedhypothetical digestive effect on the red cel membraneas a whole, or " an effect on a substance, probablya serum protein intimately bound into the surfaceof the red cells, possiblv crystalbumin" as suggestedby Wiener and Katz (1951)
Furthermore, when ' enzyme-treated cells " are
mixed with sensitized cells, agglutination will onlytake place if the enzyme-treated cells contain thespecific antigenic component. If the action oftrypsin were to modify the red cell surface as a
whole, then one would have expected that, if such a
mixture of cells agglutinated at all, agglutinationwould occur independently of any specific antigen-antibody combination.By using a pure saline anti-D serum or a saline
anti-A, it can be shown that trypsinized cells donot absorb complete antibody more avidly thanuntreated ones, and, correlated with this fact, thetrypsin agglutination with such sera is not remark-ably different from the usual saline agglutination:in many instances it tends to be weaker.
It therefore seems logical to postulate that theincreased agglutinability of trypsin-modified redcells by incomplete antibody is related to theircapacity to absorb more antibody and that theeffect of trypsin is to modify the antigen loci in sucha way as to promote increased union between themodified loci and incomplete antibody. It wouldappear that fresh cells absorb complete antibodymaximally and hence trypsinization has littleeffect.
It is proposed that agglutination depends upon a
quantitative union between antigen and antibody:that a certain minimum degree of union is neededbefore agglutination can take place: and further-more, that there is an optimum degree of unionbeyond which agglutination is not further enhanced.
It is unnecessary to postulate univalent andbivalent antibodies, and it is suggested that, in fact,all antibodies are structurally alike and are
bivalent. The difference between them is a quanti-tative rather than a qualitative one, for, whereas thecomplete antibody possesses two fully reactivevalencies, incomplete antibodies usually have one,
on rare occasions two, weakly reactive valencies.The latter form, which has been referred to as
"doubly incomplete antibody," explains those rare
instances where the Coombs test is negative andonly becomes positive when the cells are firsttrypsin-treated.With complete antibody union is optimal, but
with incomplete antibody the antigen-antibody
union is sub-minimal (sensitization) and so agglu-tination cannot take place although a certainamount of antibody has been absorbed. Trypsinmodifies the antigenic loci so that increased unionbetween these modified loci and the weakly reactingvalence of the incomplete antibody can take place.
Sensitized cells suspended in trypsin-saline willonly agglutinate feebly and to low titre, but theirsuspension in trypsin albumin-plasma greatlyenhances sensitivity and strength of reaction asshown in Table IV. They will also agglutinate inalbumin-plasma mixture alone though much lessstrongly than in the presence of trypsin. It can alsobe shown that the substitution of immune humangamma globulin for albumin-plasma in the trypsintest wilt effect similar enhancement of the aggluti-nation reaction, whereas bovine albumin is withouteffect.Thus it is apparent that, for optimal specific
trypsin agglutination to occur, at least two factorsare needed: (i) Trypsin modification of the red cells,probably a focal action at the haemagglutinogenloci, optimal trypsin concentration and incubationtime being necessary. (ii) The potentiating effectof a " colloid factor," possibly a gamma globulinfraction. This colloid factor does not have anydirect action on the red cells. It presumably acts as acomplementary factor or linkage, in the presence ofwhich the weakly reacting valence of the incompleteantibody is enabled quantitatively to increase itsunion with the unchanged antigen loci to a degreesufficient for agglutination to take place.
Application of the Concurrent Trypsin-tube Test toRoutine Clinical Studies
Opportunities for clinical trial have been limitedto the study of its value and reliability as a sensitivemethod for routine Rh grouping, and for thedetection of incomplete antibodies in sera, but theresults obtained have been encouraging and themethod is so simple and easy to perform. One ofthe reasons why the standard trypsin test has notbeen generally used may be because of the extramanipulations involved, and so the clinical resultswith the concurrent trypsin tube test may be ofinterest.
Routine Rhesus Grouping.-A series of 1,000bloods have been tested in parallel by the trypsin-saline and standard saline tube tests.The incomplete anti-D serum for the trypsin test
is used suitably diluted. If desired, each new batchof albumin anti-D can be titrated and the dilutionchosen which gives strong and clear-cut agglutina-tion with D+ cells. As a routine the albumin
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STUDIES ON CONCURRENT SENSITIZATION AND TRYPSINIZATION
grouping serum supplied by the Lister Institu-tediluted 1:10 with saline has been used. This gives a
final serum dilution of 1: 25 for the actual tests.Using such diluted serum nearly all Du bloods
will show as D negative. The test, however, is
sensitive for Du, and one strongly reacting Du,which was negative by the saline method, gave a
weak trypsin agglutination.Initially readings were recorded after two hours'
incubation while checks were being made to deter-mine the minimum incubation time which wouldnot affect the reliability of the method. It was foundthat centrifuging the tubes after 10 minutes andthen making the readings gave only 85-90%accuracy, but if the tubes were incubated for 20minutes, then centrifuged, and replaced in thewater-bath for a further five minutes, the resultswere the same as those obtained by the full two
hours' incubation, although the latter were stronger
and clearer cut. A comparison of the 20-minuteand two-hour readings has been made on the last300 blood groups without any discrepancy resulting.
All negatives were checked microscopically andthis is regarded as important. The results were as
follows:
Rh Positive Rh Negative
Saline tube test .. .395 105Trypsin , ,, 396 104
The trypsin test gave a weak positive with a sampleof cord blood which was negative to the saline test.This was subsequently confirmed as a Du infantfrom a known Du mother.
Du Screen Tests.-The 105 rhesus-negativebloods were screened independently by one of mycolleagues by the Coombs test which gave a positivereaction with six of them, one of these being theDu cord blood already referred to.The five remaining positives were retested by the
trypsin-saline method using neat, instead of diluted,albumin anti-D serum. The results show that a
very weakly reacting Du blood was not detectableby the test, but neither did the standard trypsin testgive a positive reaction with this blood. Moreover,
when a 1: 2.5 dilution of the albumin anti-D was
used to sensitize the cells, the Coombs test was alsonegative. On the other hand, two false positiveswere recorded by the Coombs method which were
negative in trypsin-saline. Thus emphasis is againlaid upon the fact that these two tests should alwaysbe considered as complementary to one ano:her.The results follow.
Coombs Trypsin-Test saline Remarks
Mrs. B. .. +- + Confirmed DuMrs. Y .. + + + Confirmed DuMrs. Ba + Neg. Weak Du confirmed by Lister
InstituteMrs. G. . + Neg. Not Du. Cells coated with incom-
plete cold antibodyMrs. W. Neg. Not Du. Cold incomplete antibody
Routine Antibody Screening Test for AntenatalCases.-Five hundred and thir-ty antenatal sera from376 D+ and 154 D-negative mothers were screenedby the trypsin-saline test. The negative sera werechecked independently by the Coombs test. Anti-bodies were detected in five negative sera by bothmethods.One case was interesting because the agglutinin
was extremely weak and not present in saline oralbumin. Moreover, variable results were obtainedwhen it was tested against six different D+ bloods,three of these being positive and three negative withboth trypsin-saline and Coombs. The agglutininwas confirmed as anti-D, and it was thought that itwas so weak that it could only be shown whenstrongly reacting D+ cells were used. It did notreact with a Du blood.As previously mentioned, an increased incomplete
cold antibody can be demonstrated in occasionalcases if the tubes are centrifuged after the two-hourincubation period. The significance of its occurrencein occasional cases in pregnancy with a thermalrange of activity only slightly below 370 C. is notknown, but it does emphasize the importance ofusing a water-bath and not an incubator whenperforming trypsin tests, because trypsin-treatedcells are highly sensitive to cold agglutinins, andthese can frequently mislead the unwary.
Antibody Titration.-The test has also been usedfor the study of antibody patterns during pregnancyand gives results which closely parallel thoseobtained by the standard trypsin method. Whenperformed in the presence of albumin-plasma(T.A.P.) the agglutination reactions are accen-tuated, particularly for weak antibodies. The end-point is clear and sharp, being usually microscopi-cally positive only one, or at'the most two, tubeshigher than the naked-eye reading.Comparative titrations of three random cases by
different methods are given:
Trpi-Trypsin-Saline Albumin A.H.G. Trypsin sTrypin- albumin-saieplasmaMrs. P. 1 8 Nil 1 4 1 10 1 5 1 10Mrs. A. Tr. 1 160 1.160 1 160 1 160 1 160Mrs. G. 1,8 1 5 1'2 1,5 1 5 120
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Direct Compatibility Tube Test.-This test ismore sensitive than the usual albumin cross-matching technique and it is recommended that atrypsin-saline test at 370 C. be included as a routinemethod. In one recent instance, an intra-group Aincompatibility due to a1 was readily detectableusing this method.
DiscussionFor the routine investigation of antenatal cases,
the trypsin-saline test has proved itself to be highlysensitive, specific, and reliable, and it is consideredsuperior to the saline or albumin methods.
It is simple and, moreover, possesses the greatadvantage that an albumin-agglutinating serum canbe used for routine grouping of saline cell suspen-sions with the minimum of effort. Furthermore, thetest is economical inasmuch as the grouping serumcan be used diluted 10-15 times, and a capillarydropping pipette for measuring the volumes enablesone to group five to seven bloods per drop ofgrouping serum.
It is desirable that Du bloods should not beclassed as D+ on initial grouping, and this mightappear to be a valid objection to the routine employ-ment of this test. However, with diluted albuminanti-D, only a strongly reacting Du blood is likely toagglutinate, and this agglutination is weak (almostmicroscopic) in comparison with the strong agglu-tinates obtained with D+ bloods. Such weaklyreacting bloods should arouse suspicion and bechecked with a saline anti-D.An added attraction is the simplicity and speed
with which all antenatal sera can be screened for thepresence of antibody using a number of differenttest cells if desired, and, moreover, any serum foundto contain antibody can be readily tested against abattery of cells of known genotypes without thelabour of having to trypsinize them all separatelybeforehand.As an additional precaution for cross-matching, it
is ideally simple and obviates the necessity of having
to perform a Coombs test, since it will detect thosetypes of weak incompatibility which are not usuallypicked up in albumin.
Finally, it is suggested that it will be found to bevaluable both for direct and indirect testing inhaemolytic states, and the direct trypsin-albumin-plasma test was positive in a recent case of acutedisseminated lupus with anaemia.
SummaryA modification of the use of trypsin for routine
Rhesus grouping and antibody detection with thedevelopment of two tube-tests, trypsin-saline andtrypsin-albumin-plasma, is described.The two new methods have the advantage of
simplicity and save both time and labour in routinework. For Rhesus grouping the use of a dilutedalbumin anti-D is a great advantage and a con-siderable economy of serum.
Experience gained from experimental investiga-tions and the results obtained in clinical studieshave shown that the method is as sensitive, specific,and reliable as the standard trypsin and Coombstechniques, and far superior to albumin agglutina-tion.The marked enhancement effect of albumiD-
plasma, especially for direct tests, is noted, and thenature of the trypsin-agglutination mechanism isdiscussed in the light of this.The method is suitable for the investigation of
haemolytic disease and for direct matching compati-bility tests, in which latter it is considered farsuperior to the present albumin technique.
REFERENCESDacie, J. V. (1954). The Haemolytic Anaemias, p. 237. Churchill,
London.Dausset, J. (1952). Blood, 7, 818.Delezenne, C., and Pozerski, E. (1903). C.R. Soc. Biol. (Paris), 55,
327.Hubinnot, P. 0. (1951). Nature (Lond.), 167, 278.Morton, J., and Pickles, M. M. (1947). Ibid., 1590 779.
(1951). Journal of Clinical Pathology, 4, 189.Wheeler, W. E., Luhby, A. L., and Scholl, M. L. L. (1950). J.
Immunol., 65, 39.Wiener, A. S., and Katz, L. (1951). Ibid., 66, 51.
242.
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athol: first published as 10.1136/jcp.10.3.236 on 1 August 1957. D
