B cells and plasma cells are the major cell types involved in the production of antibodies. Antibodies are easily measured in the laboratory and are often used as an indication that a patient has developed immunity against a pathogen.
Depending on the cytokine profile and the type and location of the tissue infected, antibody production can vary as to its class. You've most likely heard of the five classes of antibodies: IgG, IgM, IgA, IgD, and IgE. Once immunity is established by a vaccine, the most secreted antibodies are usually class IgG and IgM, which are found mainly in the bloodstream and tissue fluids. However, class IgA typically protects mucosal surfaces and would be useful in protecting us from respiratory infections. Creating vaccines that stimulate IgA is a challenge and would probably require different delivery systems—the most common vaccine delivery currently is injection.
T cells, as we saw earlier, are needed to help B cells in the antibody response. In addition, T cells are the primary mediators of cell-mediated immune responses, which are important in defense against intracellular pathogens. Unfortunately, T cell responses are more difficult to measure and are usually only tested in research laboratories.
It can be stated conclusively that no matter what type of response, the development of immune memory is key to an effective vaccine. Also, since some pathogens can cause a very rapid infection and even the memory response might not catch it in time, many vaccines require multiple injections called boosters to help strengthen and speed up the response.
