18.1 Vaccines

• Records indicate that from at least the 1400s onwards, they had children inhale dried smallpox scabs which usually resulted in mild disease, followed by immunity called variolation.

• A vaccine is a suspension of organisms or fractions of organisms used to induce immunity.

  • Development of vaccines based on the model of the smallpox vaccine is the single most important application of immunology.

  • An effective vaccine prevents the targeted disease from ever occurring, thereby ceasing suffering before it ever begins.

• Many communicable diseases can be controlled by behaviors and environmental methods.

  • If prevention fails, bacterial diseases can often be treated with antibiotics.

• If a high percentage of the population is immune, a phenomenon called herd immunity, outbreaks are limited to sporadic cases because there are not enough susceptible individuals to support the spread of epidemics.

• To create effective vaccines, the developers need to overcome a number of hurdles: understanding the most effective antigens that will cause an immune response, fully understanding the life cycle of stages of microorganism, finding effective animal models to test efficacy, and funding and coordinated research on a particular vaccine.

• Deliberate weakening, called attenuation can lead to the production of live attenuated vaccines.

• Inactivated killed vaccines use whole microbes that have been killed, usually by formalin or phenol, after being grown in the laboratory.

• Subunit vaccines contain only selected antigenic fragments of microorganisms that best stimulate an immune response.

• Toxoid vaccines contain inactivated toxins produced by a pathogen.

• Virus-like Particle Vaccines resemble intact viruses by not containing any viral genetic material.

• Recombinant vaccines, DNA vaccines, and recombinant vector vaccines do not need a cell or animal host to grow the vaccine’s microbe.

  • This avoids the problems involved in using live attenuated virus, including egg protein in a vaccine, or the difficulty of propagating certain viruses in cell culture

• Most current vaccines, especially the inactivated or subunit vaccines, act by causing the production of humoral antibodies.

18.2 Diagnostic Immunology

• Sensitivity is the probability that the test is reactive if the specimen is a true positive.

• Specificity is the probability that a test will not be reactive if a specimen is a true negative.

• Immunology gives us many other invaluable diagnostic tools, most of which are based on interactions of humoral antibodies with antigens.

  • The main problem that must be overcome in antibody based diagnostic tests is that antibodies cannot be seen directly.

• Combining an “immortal” cancerous B cell with an antibody-producing normal B cell creates a hybridoma that, when grown in culture, produces the type of antibody characteristic of the ancestral B cell indefinitely.

• Monoclonal antibodies have also become a clinically important, frequently used class of drugs.

• Even humanized antibodies can cause unwanted immune responses, which has spurred research and development of fully human antibodies.

  • One approach has been to genetically modify mice so they contain human antibody genes.

• Precipitation reactions involve the reaction of soluble antigens with IgG or IgM antibodies.

  • If they are allowed to diffuse together, an immunodiffusion test, or precipitation ring test will show a cloudy line of precipitation in the area in which the optimal ratio has been reached (the zone of equivalence).

• The techniques of immunodiffusion and electrophoresis can be combined in a procedure called immunoelectrophoresis.

  • The procedure is used in research to separate proteins in human serum and is the basis of certain diagnostic tests

• Fluorescent-antibody (FA) techniques can identify microorganisms in clinical specimens and can detect the presence of a specific antibody in serum

• Direct fluorescent antibody (FA) tests are usually used to identify a microorganism in a clinical specimen

• Indirect fluorescent-antibody (FA) tests are used to detect the presence of a specific antibody in serum following exposure to a microorganism

• The FACS is a modification of a flow cytometer, in which a suspension of cells leaves a nozzle as droplets containing no more than one cell per drop

• An interesting application of the flow cytometer is sorting sperm cells to separate male (Y-carrying) and female (X-carrying) sperm.

• A common use of the direct ELISA test is to detect the presence of drugs in urine

• Western blotting, often simply called immunoblotting, can identify a specific protein in a mixture (such as proteins extracted from a blood sample).

  • The components of the mixture are separated by electrophoresis in a gel and then transferred to a protein-binding sheet (blot).

• The diseases that most of these diagnostic methods target are also those that are more likely to be found in developed countries