Active and Passive Immunity (1).pdf

Active and Passive Immunity Samuel Addo Akwetey Department of Clinical Microbiology Learning objectives At the end of the lecture, students are expected to: Know the differences between vaccination, immunization and inoculation Understand the concept...

Active and Passive Immunity Samuel Addo Akwetey Department of Clinical Microbiology Learning objectives At the end of the lecture, students are expected to: Know the differences between vaccination, immunization and inoculation Understand the concept of active immunity Understand the concept of passive immunity Antigenicity and Immunogenicity Vaccination, Immunization and Inoculation According to the Center for Disease Control and Prevention, Vaccination is the act of introducing a vaccine into the body to produce protection from a specific disease. Immunization is a process by which a person becomes protected against a disease through vaccination. Inoculation is a set of methods of artificially inducing immunity against various infectious diseases. Inoculation is the act of implanting a disease inside a person or animal. Active immunity Active immunity is a host immune response induced after contact with foreign antigens (e.g., microorganisms). This contact may consist of clinical or subclinical infection (Naturally- acquired), immunization with live or killed infectious agents or their antigens, or exposure to microbial products (Artificially-acquired). The host actively produces an immune response consisting of antibodies and activated T lymphocytes. The main advantage of active immunity is that resistance is long term. Its major disadvantage is its slow onset, especially the primary response. Active immunity – Natural and Artificial Passive immunity Passive immunity is accepted passively by the host in the form of immune components that were preformed in another host. Hospital emergency departments have supplies of antibodies against toxins from infectious agents that cause tetanus, botulism etc. Passive immunity can even occur between species, as when snake-bite victims (usually humans or dogs) are given the antibody-rich serum from an animal (usually horse or sheep) that was previously inoculated with the venom so that the serum contains high levels of specific anti-venom antibodies.  Passive immunity Preformed antibodies to rabies and hepatitis A and B viruses can be injected to neutralize virus and thereby control viral multiplication (Artificially- acquired). Other forms of passive immunity are IgG passed from mother to fetus during pregnancy and IgA passed from mother to newborn during breastfeeding (Naturally-acquired). The main advantage of passive immunization is the prompt availability of large amounts of antibody. Disadvantages are short life span of antibodies and possible hypersensitivity reactions if serum from another species is used. Passive immunity – Natural and Artificial Passive–active immunity In passive–active immunity, a patient gets both preformed antibodies to provide immediate protection and a vaccine to provide long-term protection. These preparations are given at different sites in the body to prevent the antibodies from neutralizing the vaccine. This approach is used to prevent tetanus, rabies, and hepatitis B. Summary  Antigens and Immunogens An immunogen is any molecule that induces an immune response. Antigens are immunogens that react with the highly specific receptors on T cells or B cells. They are also substances that stimulate the production of antibodies. Antigens bind to specific lymphocyte receptors, whether or not they stimulate immune responses. Not all antigens are immunogenic. Immunogenicity is based on; Foreignness High molecular weight (100,000 g/mol) Chemical–Structural Complexity (heteropolymers) Antigenic determinants (Epitopes): Antibodies bind epitopes that are roughly five amino acids or sugars in size, whereas T-cell receptors bind epitopes between 8 and 17 amino acids in size. Dosage, Route, and Timing of Antigen Administration Age and Immune response Immunity is less than optimal at both ends of life. In newborns, natural barriers until 3 to 4 weeks, and innate cells are less sensitive to proinflammatory cytokines and chemokines. Newborns actually have higher number of circulating lymphocytes than adults, but these are individually less effective. IgG and IgA production begins after birth and only reaches protective levels at around 1 year. The precise reason why newborns have reduced immunity is unknown even though there are some speculations. Immunity declines with age. The thymus begins to atrophy after puberty. There is a reduced IgG response to certain antigens, and the immune responses to certain vaccines and infections are blunted due to the exhaustion of B cells. In the elderly, there is reactivation of latent infections and increased frequency of autoimmune diseases due to the decrease in regulatory T cells. Haptens A hapten is a molecule that is not immunogenic by itself but can react with specific antibody. Haptens can be small molecules, nucleic acids, lipids, or drugs (e.g., penicillins). Although haptens cannot stimulate a primary adaptive response by themselves, they can do so when covalently bound to a “carrier” protein.