which vaccine is more heat sensitive bcg or opv?
What is vvm?
What is shake test?
How is vaccine stored in ilr?
What happens once a vaccine is administered to a vaccinee?
Following injection, the vaccine antigens attract local and systemic dendritic cells, monocytes and neutrophils. These activated cells change their surface receptors and migrate along lymphatic vessels, to the draining lymph nodes where the activation of T and B lymphocytes takes place. In case of killed vaccines there is only local and unilateral lymph node activation. Conversely for live vaccines there is multifocal lymph node vaccination due to microbial replication and dissemination. Consequently the immunogenicity of killed vaccines is lower than the live vaccines; killed vaccines require adjuvants which improve the immune response by producing local inflammation and recruiting dendritic cells/monocytes to the injection site.
Secondly, the site of administration of killed vaccines is of importance; the intramuscular route which is well vascularised and has a large number of patrolling dendritic cells is preferred over the subcutaneous route. The site of administration is usually of little significance for live vaccines.
Finally due to focal lymph node activation, multiple killed vaccines may be administered at different sites with little immunologic interference. Immunologic interference may occur with multiple live vaccines unless they are given on the same day/at least 4 weeks apart or at different sites.
What are the immune responses of T cell-independent antigens (i.e. polysaccharide vaccines) at the cellular level?
On being released from the injection site these antigens usually non-protein, polysaccharides in nature, reach the marginal zone of the spleen/nodes and bind to the specific Ig surface receptors of B cells. In the absence of antigen-specific T cell help, B cells are activated, proliferate and differentiate in plasma cells without undergoing affinity maturation in germinal centers. The antibody response sets in 2–4 weeks following immunization, is predominantly IgM with low titers of low affinity IgG. The half life of the plasma cells is short and antibody titers decline rapidly. Additionally the PS antigens are unable to evoke an immune response in those aged less than 2 years due to immaturity of the marginal zones. As PS antigens do not induce germinal centres, bona fide memory B cells are not elicited. Consequently, subsequent re-exposure to the same PS results in a repeat primary response that follows the same kinetics in previously vaccinated as in naïve individuals.
What are the immune responses of T cell-dependent antigens at the cellular level?
T cell-dependent antigens include protein antigens which may consist of either pure proteins (Hepatitis B, Hepatitis A, HPV, Toxoids) or conjugated protein carrier with PS antigens (Hib, meningo, pneumo). The initial response to these antigens is similar to PS antigens. However the antigen-specific helper T cells that have been activated by antigen-bearing dendritic cells trigger some antigenspecific B cells to migrate towards follicular dendritic cells (FDC’s), initiating the germinal center (GC) reaction. In GC’s, B cells receive additional signals from follicular T cells and undergo massive clonal proliferation, switch from IgM towards IgG/IgA, undergo affinity maturation and differentiate into plasma cells secreting large amounts of antigen-specific antibodies. Most of the plasma cells die at the end of germinal centre reaction and thus decline in antibody levels is noted 4-8 weeks after vaccination. However a few plasma cells exit nodes/spleen and migrate to survival niches mostly located in the bone marrow, where they survive through signals provided by supporting stromal cells and this results in prolonged persistence of antibodies in the serum
Superintendent, ICH.