Chapter 6 Immunization

Immunization Two Artificial Methods of Immunity Active immunization – administration of a vaccine so that the patient actively mounts a protective immune response Passive immunization – individual acquires immunity through the transfer of antibodies formed by an immune individual or animal

Immunization Brief History of Immunization The Chinese noticed that children who recovered from smallpox did not contract the disease again They infected young children with material from a smallpox scab to induce immunity in these children, a process known as variolation The use of variolation spread to England and America but was stopped due to risk of death

Immunization Brief History of Immunization 1796 – Edward Jenner discovered process of vaccination by inoculating material from a person infected with cowpox 1879 – Louis Pasteur developed a vaccine against Pasteurella multocida Practice of transferring antibodies was developed when it was discovered vaccines protected through the action of antibodies

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Immunization Brief History of Immunization Socioeconomic and political problems prevent many developing nations from receiving vaccines Effective vaccines unable to be developed for some pathogens Vaccine-associated risks discourage investment in developing new vaccines

Immunization Active Immunization Vaccine types Attenuated (live) vaccines Use pathogens that have reduced virulence Can result in mild infections but no serious disease Contain active microbes that stimulate a strong immune response due to the large number of antigen molecules Can provide contact immunity through vaccinated individuals infecting those around them Can be hazardous because modified microbes may retain enough residual virulence to cause disease

Immunization Active Immunization Vaccine types Inactivated (killed) vaccines Whole agent vaccines – produced with deactivated but whole microbes Antigenically weak because the microbes don’t reproduce and don’t provide many antigenic molecules to stimulate the immune response Often contain adjuvants, chemicals added to increase the effective antigenicity

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Immunization Active Immunization Acellular vaccine – contain only certain component of microbes, Toxoid vaccines Chemically or thermally modified toxins used to stimulate active immunity Useful for some bacterial diseases Stimulate antibody-mediated immunity Require multiple doses because they possess few antigenic determinant Subunit vaccines – produced with antigenic fragments of microbes Both types are safer than live vaccines because they cannot replicate or mutate to a virulent form Conjugate vaccine

Immunization Active Immunization Vaccine types Vaccines using recombinant gene technology Research attempts to make vaccines that are more effective, cheaper, and safer A variety of recombinant DNA techniques can be used to make improved vaccine

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Immunization Active Immunization Vaccine safety Problems associated with immunization Mild toxicity most common Pain at injection site or, in rare cases, general malaise or fever high enough to induce seizures Risk of anaphylactic shock (severe allergic reaction) Residual virulence from attenuated viruses Allegations that certain vaccines against childhood diseases cause or trigger autism, diabetes, and asthma Research has not substantiated these allegations

Immunization Passive Immunotherapy Administration of antiserum containing preformed antibodies to a patient. Can be – gamma globulin portion containing antibodies Hyperimmune sera- ( g-globulins from selected donor) Antitoxin- antibodies against specific toxins , tetanus,diphteria Used to provide immediate protection against a recent infection or an ongoing disease Antisera has several limitations, including Contains antibodies against many antigens Can trigger allergic reactions called serum sickness May be contaminated with viral pathogens Antibodies of antisera are degraded relatively quickly Limitations are overcome through development of hybridomas

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Immune Testing Uses serology – study and diagnostic use of antigen-antibody interactions in blood serum Uses immunological processes in two general diagnostic ways Uses known antibodies to detect antigens associated with an infectious agent Uses antigens to detect specific antibodies in a patient’s blood to determine exposure to a specific pathogen Test chosen based on the suspected diagnosis, cost to perform the test, and the speed with which a result can be obtained

Immune Testing Precipitation Tests One of the easiest of serological tests Relies on fact that antigens and antibody mixed in the proper proportion form large macromolecular complexes called precipitates Correct proportions are important to create precipitation Two techniques determine optimal antibody and antigen concentrations Immunodiffusion Immunelectrophoresis

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Immune Testing Precipitation Tests Radial immunodiffusion Used to measure the concentrations of specific antibodies or immunoglobulins in a person’s serum Produces anti-antibodies – inject human antibodies into an individual of another species, where they will be antigenic and cause production of antibodies directed against the human antibodies The human antibodies are the “antigen” in the test, and the anti-antibody is the antibody

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Immune Testing Precipitation Tests Immunoelectrophoresis Improves the resolution of an immunodiffusion test Can resolve more than 30 distinct antigens at once Commonly used to demonstrate the absence of a normal antigen or to detect the presence of excessive amounts of an antigen

Immune Testing Agglutination Tests Agglutination occurs due to the cross-linking of antibodies with particulate antigens Agglutination is the clumping of insoluble particles, whereas precipitation involves the aggregation of soluble molecules These reactions are easy to see and interpret with the unaided eye Hemagglutination, the agglutination of red blood cells, can be used to determine blood type

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Immune Testing Neutralization Tests Viral neutralization Cytopathic effect – viruses introduced into appropriate cell cultures will invade and kill the cells Ability of virus to kill culture cells is neutralized when virus is first mixed with antibodies against it Absence of cytopathic effect indicates the presence of antibodies against the virus Test is sensitive and specific enough to identify whether an individual has been exposed to a particular virus or viral strain

Immune Testing Neutralization Tests Viral hemagglutination inhibition test Useful for viruses that aren’t cytopathic Based on viral hemagglutination, the ability of some viral surface proteins to clump red blood cells Serum from an individual will stop viral hemagglutination if the serum contains antibodies against the specific virus Commonly used to detect antibodies against influenza, measles, and mumps

Immune Testing The Complement Fixation Test Based on the generation during complement activation of membrane attack complexes that disrupt cytoplasmic membranes Used to detect the presence of specific antibodies in an individual’s serum Can detect antibody amounts too small to be detected by agglutination

Immune Testing

Immune Testing Labeled Antibody Test Uses antibody molecules that are linked to some molecular “label” that enables them to be easily detected Used to detect either antigens or antibodies

Immune Testing Labeled Antibody Test Fluorescent antibody tests Use fluorescent dyes as labels Fluorescein is the most important dye used in these test Fluorescein-labeled antibodies used in two types of tests Direct fluorescent antibody test Indirect fluorescent antibody tests

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Immune Testing Labeled Antibody Test ELISAs Stands for enzyme-linked immunosorbent assay Uses an enzyme as the label Reaction of the enzyme with its substrate produces a colored product indicative of a positive test Most common form of ELISA is used to detect the presence of antibodies in serum

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Immune Testing Labeled Antibody Test ELISAs Antibody sandwich ELISA Modification of the ELISA technique Commonly used to detect antigen Antigen being tested for is “sandwiched” between two antibody molecules

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Immune Testing Labeled Antibody Test ELISAs Advantages of the ELISA Can detect either antibody or antigen Can quantify amounts of antigen or antibody Easy to perform, inexpensive, and can test many samples quickly Plates coated with antigen and gelatin can be stored for later testing

Immune Testing Labeled Antibody Test Western blot test Technique for detecting antibodies against multiple antigens in a complex mixture Can detect more types of antibodies and is less subject to misinterpretation than other tests

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Immune Testing Recent Developments in Immune Testing Simple immunoassays that give results in minutes Useful in determining a preliminary diagnosis Most common are immunofiltration and immunochromatography assays Immunofiltration Rapid ELISA that uses antibodies bound to membrane filters rather than polystyrene plates Membrane filters have large surface area making the assay quicker to complete

Immune Testing Recent Developments in Immune Testing Immunochromatography Very rapid and easy to read ELISAs Antigen solution flows through a porous strip where it encounters antibody labeled with either pink colloidal gold or blue colloidal selenium Antigen-antibody immune complexes flow through a region and encounter antibody against them, resulting in a visible pink or blue line Used in pregnancy testing to detect human chorionic growth hormone

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