IMMUNITY AND ELISA

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

IMMUNITYInnate immunity

Nonspecific

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

Figure 17.1

ANTIBODIESGlobular 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)

SCHEMATIC OF HIV VIRION

Figure 16-11b

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.