 Study of the immune system  How the body protects itself against foreign, potentially disease-causing microorganisms  Three main functions:  To recognize intruders  To respond appropriately to intruders in a way that protects the body  To respond the next time the intruders are encountered

Innate immunity Nonspecific Adaptive Immunity Specific Induced resistance to a specific pathogen Humoral versus cell-mediated B cells versus T cells

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) Specificity Each bacterial cell has many different epitopes

Figure 17.1

Globular proteins (immunoglobulins) made by B cells in response to an antigen Highly specific Antigen-binding sites

 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

 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)

Figure 16-11b

 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 involves using the principles of the immune system or antibody—antigen reaction to diagnose diseases or detect antigens in bodily fluids  Important diagnostic tests  Direct agglutination  Indirect agglutination  Hemagglutination  ELISA

 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.

 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

 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 works  Microplates Made of polystyrene which binds proteins by hydrophobic interaction.  Primary and secondary antibodies  Color producing enzyme substrate

Modified from Specter, S. C., R. L. Hodinka and S. A. Young. Clinical Virology Manual, Third Edition. ASM Press, 2000.