Adaptive Immunity

Active and Passive Immunity

Infection and vaccination are forms of active immunity that cause the body to generate antibodies. Passive immunity results from the transfer of antibodies from one person to another.
During an immune response, B cells, adaptive immune cells that mature in the bone marrow, are activated by antigen-presenting cells, which display antigens on MHC molecules, rapidly proliferate, and begin to secrete antibodies, circulating proteins that recognize a specific antigen, or foreign substance in the body. Antibody-producing plasma cells, a type of mature B cell that has previously encountered an antigen, maintain this antibody response to protect a person against recurrent infections for weeks to years.

Antibody Mediated Immunity

Antibodies are an important part of the adaptive immune system. The presence of antibodies marks pathogens for destruction by macrophages. Antibodies can also activate the complement system, which also results in the destruction of the pathogen.
Infections and vaccination are the ways that antibodies can be generated in a person's body. In either case, the response that is induced is the same in that there is a rapid secretion of antibodies as well as the formation of a long-lasting plasma cell and memory B cell response. Both infection and vaccination are forms of active immunity because the body actively generates an immune response that is specific to a particular pathogen and arises after an immunizing event.

Not all antibodies in a person's bloodstream are a result of an infection or vaccine. Passive immunity results from the transfer of antibodies from one person to another. This type of antibody response is short-lived but provides important protection in times when a person is unable to generate an immune response on their own. For example, a newborn cannot make its own immune response for a few months after being born, so the mother's antibodies are transferred to the baby through the placenta before birth, and through breast milk after birth, to protect the baby from infection until it has developed its own immune system. Passive immunity can also be utilized in immunocompromised individuals who cannot generate their own antibodies, such as those with selective immunoglobulin M deficiency.