Chapter Abstract

Discoveries about the components and functions of the immune system have been applied not only to medical practices, but to other areas as well. Immunization involves manipulating the immune system to our advantage. The more we understand about how the body resists disease the greater the opportunities to improve means to prevent, diagnose, treat, and cure many diseases. Vaccination involves stimulating an active immune response by administering antigens foreign to the host. Vaccine can include a variety of microscopic organisms or materials taken from such organisms. Antigens are not only used to vaccinate, but they are also essential for many diagnostic tests. Known antigens and known antisera are used in a number of procedures that provide evidence of infection or exposure to many types of diseases, both infectious and noninfectious. Antisera (e.g. immunoglobulin, gamma globulin, etc) are often used for passive immunization when the situation calls for immediate protection of the host (e.g. snake bite, Hepatitis A exposure, etc). Most tests are performed in vitro. although some can be performed in vivo.

Learning Objectives

• Explain how knowledge of how the immune system works can be applied to prevention of infectious diseases.
• Describe the difference kinds of substances commonly used as vaccines.
• Explain how having antiserum (antibodies) or known specificity or known antigens can be used to detect a patient's exposure to a certain disease agent.
• Describe how an awareness of anamnesis is important to planning a vaccination regimen.
• Describe four in vitro serological tests commonly employed in the clinical laboratory.
• Describe an example of an in vivo serological test

Lecture Outline - Specific Immunity

I. Practical Applications of Immunity

    A. Production of antisera and vaccines

    B. Development of reagents for diagnostics and therapeutics

II. Types of Immunity

    A. Artificial Passive immunity

        1. immune components from donors

            a. immune serum (ISG)

            b. specific immune globulin (SIG)

            c. B-cells and T-cells

        2. protection is immediate but relatively short duration

        3. e.g. injection of ISG or SIG, or B-cells and T-cells

    B. Artificial Active immunity

        1. immune components actively produced by host in response to antigen

            a. takes time to develop

            b. protection longer-lasting

        2.. vaccines stimulate active immune response in host

            a. must induce protection

            b. must not cause disease or harm recipient

    C. Natural Active Immunity

                1. active infection, acquired via natural (uncontrolled) exposure

                2. e.g. childhood diseases, subclinical infections - sometimes re-infections

    D. Natural Passive Immunity

                1. e.g. prenatal (~99%), transplacental antibody (IgG)

                2. e.g. postnatal (~1%), mother's milk (especially intestinal protection)

III. Vaccine Components

    A. killed or inactivated microbes

    B. live, attenuated microbes

    C. subunit vaccines

        1. flagella

        2. capsular proteins

        3. cell wall components

        4. viral components

    D. genetically engineered microbes or parts thereof

IV. Vaccination - why? who? when?

    A. prevent / stop spread of infection

        1. increase specific antibody levels (=titers)

        2. protect susceptible individuals

        3. protect susceptible populations

                a. Herd Immunity

    B. influential factors

       1. severity of threatening disease

        2. age of population

            a. childhood diseases

            b. "at risks" individuals / groups

                (1) elderly

                (2) very young

        3. compromised immunity

        4. routine vaccination regimens

V. Serological Tests

    A. used detect either antibody or antigen

        1. disease agents or their products

        2. most tests involve in vitro assessments

        3. in various body fluids usually (blood, urine, spinal fluid, etc)

    B. based on visible / detectable antigen-antibody reactions

        1. agglutination

        2. precipitation

        3. immunodiffusion

        4. Immunoelectrophoresis

        5. complement fixation

        6. fluorescent antibody

        7. enzyme-linked immunosorbent assay ("ELISA")

        8. other

    C. immunoassays detect minute quantities substances

           1. antigen

            2. antibody

            3. environmental contaminants

            4. other

    D. Precise assays distinguish populations of T-cells and B-cells

    E. in vivo serological testing

            1. detect exposure to, or active infection with certain diseases

            2. Tuberculosis skin test - visible Ab-Ag reaction

                a. characteristic swelling at site of injection

natural immunity artificial immunity active immunity passive immunity

vaccine attenuation agglutination precipitation

ELISA subunit vaccine herd immunity specificity

sensitivity double diffusion serology complement fixation

immunoassays in vitro test in vivo test

Exposure to a specific disease agent?

9. Regarding antigen properties: what is the difference between an agglutination reaction and a

precipitation reaction?

10. What are the two key underlying principles of the hemagglutination inhibition test?

Give an example of an infectious agent, exposure to which, is often detected by an H.I. test?