Serodiagnosis of infectious diseases relies on the host-microbial interactions and the resulting host immune response. The immune system functions by developing a customised defence against invading micro-organisms. The immune system also has a "memory" to protect against future encounters with the same micro-organisms.
There are two arms of the immune system :- Antibody-mediated or humoral immunity and Cell-mediated or cellular immunity. Antibody-mediated immunity is the activation of a type of white blood cell called B lymphocyte which function to produce antibodies, also be called immunoglobulins. The five different classes of antibodies are IgG, IgA, IgM, IgD and IgE. Cell-mediated immunity is mediated by a second type of white blood cell called T lymphocyte. These cells destroy cells infected with micro-organisms.
Serodiagnosis of infectious diseases includes the detection of specific types of antibodies (e.g. IgG, IgM), microbial products (e.g. streptolysin produced in streptococcal infections) or the microbes themselves (e.g. antigen or DNA detection in Chlamydiae infections).