Adaptive immunity involves B cells and T cells, two types of white blood cells that circulate throughout the body to fight disease. These cells are activated by proteins found on the cell surface of antigen-presenting cells. Either an infection or deliberate introduction of antigens by vaccination can induce an adaptive immune response. This response is specific to a particular pathogen—an infectious agent, such as a strain of bacteria or virus—that can cause disease. Adaptive immunity can also be transferred via antibodies, proteins in the blood that recognize pathogens, to protect people who cannot generate an adaptive immune response themselves. Vaccines can be given to children or adults. There are four different kinds of vaccines that are used to protect against a variety of viruses and toxins.
At A Glance
Adaptive immunity is acquired only after an immunizing event, such as an infection or vaccination.
- The four stages to a specific immune response are the activation, proliferation, effector, and memory phases.
B cell differentiation occurs by random gene rearrangement that results in specificity for different antigens, and B cells rapidly proliferate after encountering their target antigen.
- B cells are formed and mature in bone marrow through V(D)J recombination and clonal selection. B cell maturation and differentiation is completed in the spleen.
- Different classes of B cells produce different antibodies with specialized functions that aid the immune reaction. B cells change the type of antibody they secrete through class switch recombination.
- Antigen-antibody binding produces protective outcomes such as cross-linking, neutralization, opsonization, complement activation, immobilization, and cellular cytotoxicity.
- The major histocompatibility complex is a series of proteins found on all cells except red blood cells; it is also known as the human leukocyte antigen system.
T cells are generated in the bone marrow, develop their specific receptors in the thymus, and are activated by antigen-presenting cells, such as B cells and macrophages.
- The types of T cells include effector, helper, memory, regulatory, mucosal-associated invariant, gamma delta, and beta selection.
- 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.
- Attenuated, inactivated, subunit, and toxoid are the types of vaccines in use today, with six variations of inactivated vaccines.