Host-Parasite Interactions

Patrick Duffy

206 256 7311

pduffy@sbri.org

Outline of class

•Antigenic variation–Background–Primary literature

•Parasite modulation of immune response–T cell epitopes and immunomodulation–Parasite modulation of DC function–Primary literature

•Parasite co-opting the immune response

•Host resistance versus host immunity

Richie & Saul 2002

Malaria life cycle

ANTIGENIC VARIATION

SULFA

Antigenic variants within strainsPlasmodium knowlesi

Brown & Brown 1965Nuri strain in Rhesus

VARIANTSPECIFICIMMUNITY

VARIANTTRANSCENDINGIMMUNITY

Brown 1973Nuri strain in RhesusAntibody-induced variation

NO VACCINE VACCINATED (variant A + IFA)

Variant-specific immunity in monkeysP. knowlesi

Par

asit

emia

Hommel 1985Saimiri monkeys

Strain AInoculum(Indo-1)

Strain BInoculum(UgPA)

Strain-specific immunity in monkeysP. falciparum

Par

asite

mia

Yount & Coggeshall 1949Joilet, IL prison studies

QUININE

Strain Ainoculum

Strain Binoculum

Strain-specific immunity in humansP. vivax

Variant antigens on the IE surfaceP. falciparum

Leech/Barnwell/Howard 1984 (P. knowlesi)

MC extract SL extract

IP with sera: SLSL MCMC

200 kD-- 1. Large MW2. Tx100 insoluble/SDS soluble3. Surface iodinatable (I125)4. Strain-specific IP

(similar to cytoadherence)

5. Trypsin-sensitive(similar to cytoadherence)

Variant surface antigen:

Serum antibodies from monkeys infected withMalayan Camp (MC) or Santa Lucia (SL) parasites

Exon-1 (Extracellular domain)

Acidic Terminal SegmentExon-2

(Cytoplasmicdomain)

Semi-conservedhead structure

Tandemassociation

TM

Tandemassociation

DBL1 CIDR1 DBL2 C2 CIDR2 ATSDBL4

DBL1 CIDR1 CIDR2 ATSDBL2

DBL5DBL3

Rosetting CD36 ICAM-1 PECAMCSA

NT

SN

TS

Exon-1

Exon-2

CR1HS

Blood group AHeparin

CD31IgMCSA

CSA/CIgG

Cell 1995Su & Wellems Smith & MillerBaruch & Howard

Many years later… PfEMP1

CD36 Binding and Non-binding PfEMP1 GroupsC

D36

bin

ding

Non

-CD

36 b

indi

ng

Joe Smith

~60 copies per haploid genomeMajority are subtelomeric

Switching inT. brucei

PRIMARY LITERATURE

Bull et al., J Infect Dis 182:252

SICK

RECOVERED

ISOLATE

SICK

RECOVERED

ISOLATE

AGGLUTINATION SCORE 0 1 2 3 4

3 MONTH OLD CHILD

26 MONTH OLD CHILD

Bull & Marsh 1999

Serum agglutination of field isolates:Evidence for variant specific immunity

FIELD ISOLATES

SE

RU

M S

AM

PL

ES

Serum agglutination of field isolates:Rare Variants and Prevalent Variants

Bull & Marsh 1999

IMMUNE MODULATION

HLA Class I molecules may be involved in liver stage immunity

Hoffman, S. L and Doolan, D. L. ( 2000) Nature Medicine

HLA Class Iantigenassociated with resistance to severe malaria

Hill et al., Nature, 1991

Expected at Parasite Rate of

CSP variant Observed 100% 50% 10%

cp26 36 58 138* 195*

cp27 405 257* 329* 378*

cp28 15 10 30 48*

cp29 16 33 89* 134*

cp26 & cp29 124 22* 22* 6*

cp27 & cp29 4 99* 53* 11

cp26 & cp27 71 171* 82 16*

cp26 & cp28 2 7 7 2 *P<.05

Frequency of CSP variants in parasites collected from 795 Gambians with malaria.

Reciprocal CTL antagonism in PBMC cultures by two naturally occurring P. falciparum CS protein variants.

Gilbert et al., Science, 1998

CS protein and HLA B35:Evidence for Host-parasiteCo-evolution?

Taylor et al., 2000

Urban et al.Figure 2

MF Good commentaryNature 1999

PRIMARY LITERATURE

Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 5

Fig. 6

CO-OPTING THE IMMUNE SYSTEM

S. mansoniexpresses host-likemolecules on its surface

Trottein, JI, 1997

Immune masking

Ig and associated complexes affinity-purified from S. mansoni with protein G

McManus, 2001

Adsorption of human Igon the surface of red cellsinfected with P. falciparum

IgG

IgM

Flick, 2001

Schistosomes develop poorly in RAG -/- mice

McKerrow 2001

S. mansoni development in mouse liver requires CD4+ T cells

McKerrow 2001

IS RESISTANCE IMMUNITY?

Resistance to malaria during childhood and adolescence

Parasitemia

Pregnancy malaria

Severe childhood malaria

Pre

vale

nc

e

Age (years)

Epidemiology and Immunity

1 10 20

0

10

20

30

40

50

60

70

80

2-5 6-10 11-15 16-25 26-40 >40

Age group (years)

migrants after 8 months exposure

migrants after 20 months exposure

Adults acquire resistance more rapidly than children

Baird 1995

Age and susceptibility

Weeks after treatment

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16

Age 12-14

Age 15-20

Age 21-35

P < 0.0001

n = 243

Volu

nte

ers

in

fecte

d (

%)

0

1

2

3

4

5

6

Tan

ner

Sta

ge

12-14 15-20 21-35

Age group (yrs)

Mea

n P

aras

item

ia

Age (yrs)

12-14 15-20 21-35

.1

1

10

100

0

P<0.01

P<0.05 P<0.01

P<0.05

DHEA-S level:lowmediumhigh

DHEA-S levels predict resistance to malaria

Culture of Plasmodium falciparum Effect of DHEAS in vitro

0

1

2

3

4

5

6

7

0 24 48 72 96 120 144

Serum+ DMSO Serum + DHEAS

Time (hours)

% P

ara

sit

em

ia

IS RESISTANCE IMMUNITY?

Resistance to pregnancy malaria

Parity-related Susceptibility to Placental Malaria(1500 deliveries in Kisumu, Kenya)

Rate (%) Mean parasite density (%IE)0

20

10

30

0

6

2

8

4

Primigravid

Secundigravid

Multigravid

Parasites infecting pregnant mothers are different than other parasites

Parasite adhesion to placenta ex vivo

Placental parasitesParasites from adult

males

Fried, Duffy 1996

Parasites of Pregnancy Malaria

Parasites of Pregnancy Malaria

BSA CSA CD36

Placenta 2 110 2

Placenta 1 103 3

Male 1 0 59

Male 4 9 143Pa

ras

ite

so

urc

e

Parasites bound*

Ex vivo assay:Placental parasites ( )bind to lining ofplacenta

*per 20 hpf

Villus

Birth weight (kg)

An

ti-a

dh

esio

n A

b L

evel

Primi Secundi Multi

-40

0

40

80

120

0

40

80

120

1.5 2.5 3.5 4.5

Antibodies and Pregnancy Outcomes

5/21

2/47LBW

LBW

Gravidity

Antibodies against Parasites of Pregnancy Malaria

Take Home Lessons

• Antigenic variation– multigene families, mechanisms differ between parasites

• Parasites modulate the immune response

• Parasites co-opt the immune system

• Resistance to parasites may or may not be immune-mediated