IMMUNOLOGY Study of the immune system How the body protects itself against
foreign, potentially disease-causing microorganisms
Three main functions:To recognize intrudersTo respond appropriately to intruders in a
way that protects the bodyTo respond the next time the intruders are
encountered
IMMUNITY
Innate immunityNonspecific
Adaptive ImmunitySpecific
Induced resistance to a specific pathogenHumoral versus cell-mediated
B cells versus T cells
ANTIGENS A substance that causes the body to produce
specific antibodies or sensitized T cells Protein or polysaccharide (lipids and nucleic
acids when combined with proteins or polysaccharides)
Found in capsule, cell walls, flagella, fimbrae, and toxins of microbes
Pollen, egg white, blood cell surface, tissue surface
Antigenic determinants (epitopes)SpecificityEach bacterial cell has many different
epitopes
ANTIBODIES
Globular proteins (immunoglobulins) made by B cells in response to an antigen
Highly specificAntigen-binding sites
HUMAN IMMUNODEFICIENCY VIRUS (HIV)
First diagnosed in 1981
Over 20 million deaths worldwide, over a half million in the United States
Over 40 million currently infected, over a million in the United States
Half of all new infections are in people younger than 25
Education has been effective in limiting the spread of HIV/AIDS
HUMAN IMMUNODEFICIENCY VIRUS (HIV)
HIV is an RNA Retrovirus
Transmitted by exchange of body fluids, sharing needles, or blood transfusion
Infects T-Cells in the immune system and thus destroys the immune system
Flu-like symptoms within 1-2 months followed by latent period of up to 10 years
HIV may have spread from an animal host to humans
Treated but not cured by drugs which inhibit the action of HIV enzymes
High error rate of replication (1/2000 nucleotides)
DIAGNOSTIC IMMUNOLOGY Diagnostic techniques help us determine
the etiology of the disease
Diagnostic techniques Microscopy
Culture Test biochemical properties of microbe
Molecular Use PCR to amplify a gene associated with the
disease
Identify the gene on a gel
Immunological
DIAGNOSTIC IMMUNOLOGY Diagnostic immunology involves
using the principles of the immune system or antibody—antigen reaction to diagnose diseases or detect antigens in bodily fluids
Important diagnostic testsDirect agglutination Indirect agglutinationHemagglutinationELISA
PRINCIPLES OF DIAGNOSTIC IMMUNOLOGY
Physician collects a sample
Antigen sample A bodily fluid that contains the infecting microbe or
the microbes toxin Urine, feces, blood, skin, pus, throat swab, mucous, etc.
Blood antiserum sample Blood antiserum contains the antibodies that the
patient made against an infection; if the patient is infected with the suspected pathogen then his/her serum has those antibodies in it.
PRINCIPLES OF DIAGNOSTIC IMMUNOLOGY
If the sample is…Antigen then the physician exposes it to pre-
made antibodies for the suspected pathogen Antibodies are produced by a rabbit that was infected
with that organism; they are collected in sterile vials and sold by pharmaceutical companies
Blood antiserum then physician exposes it to an antigen from the suspected pathogen Antigen from microorganism is prepared by
pharmaceutical company It could be a toxin, an inactivated whole agent, or any
subunit from the suspected pathogen
VIRAL SEROLOGY
Enzyme Linked Immunosorbent Assay (ELISA) Initial diagnostic test used for HIV detection
Done on women in labor before delivery to determine infection status
Patients following an accidental needlestick injury
Enzyme reacts with substrate to produce colored product Very sensitive
How ELISA worksMicroplates
Made of polystyrene which binds proteins by hydrophobic interaction.
Primary and secondary antibodiesColor producing enzyme substrate
ELISA PROCEDURES
Modified from Specter, S. C., R. L. Hodinka and S. A. Young. Clinical Virology Manual, Third Edition . ASM Press, 2000.