How does the Adaptive Immune System Function?
The main cells that are involved with the adaptive immune system are T-lymphocytes (T cells) and B-lymphocytes (B cells). These cells can be found in all tissues and circulate throughout the body through both the circulatory system and the lymphatic system. Both of these types of cells are derived from hematopoeitic stem cells. B cells undergo maturation within the bone marrow. T cells, on the other hand, undergo their maturation within the thymus. There are, generally, three stages that B and T cells can be in, depending on environmental conditions. Naive cells have matured within their respective tissues, but have not yet encountered the antigens they are specific to. Effector cells have encountered their specific antigens and have become active in the removal and elimination of their specific pathogen. Memory cells are the descendants of those cells that have eliminated their respective pathogens.
Both T cells and B cells rely on the presentation of antigens in order to become active. This presentation can occur in a number of ways. Typically, host cells and the innate immune system will assist in this process. Macrophages and other phagocytes will have taken in bacterial cells or other pathogens and partially digested them, allowing for the presentation of some of the pathogenic proteins to the cells of the adaptive immune system. Once these antigens have been recognized, a given T or B cell will either immediately activate and begin a clonal expansion (because each T or B cell is specified to a specific antigen, when they encounter that antigen they will effectively create clones of themselves in order to assist with the infection) or they will migrate to lymphatic tissue to further activate the acquired immune system.
T cells, in particular, pay attention to the presence of major histocompatibility complex on cells in order to determine whether or not a cell is self or non-self and whether there is a possible infection (such as a viral infiltration) within that cell. There are two main types of T cells: helper T cells and cytotoxic T cells. Helper T cells help to activate the rest of the immune system, to attract more cells, and to mark cells for destruction. Cytotoxic T cells are primarily designed to destroy infected cells or pathogenic cells that are causing a given infection.
B cells, on the other hand, are responsible for the triggering of the complement cascade, the attraction of other immune cells to a given area, and production of antibodies. Antibodies are, usually, free floating proteins that are used to both neutralize potential pathogens and to mark them for other cells to destroy. Mucus is comprised primarily of antibodies, which explains why it feels so sticky and congeals together.
The adaptive immune system plays a very important role in immunology. Though it is very complex, its functionality boils down to two primary distinguishing characteristics: specificity and memory. The innate immune system is very general and is not capable of the very specific and targeted response that characterizes the adaptive immune system. In addition to specificity, the memory aspect of the adaptive immune system allows it to remember antigens it has encountered in the past in order to mount a faster and stronger response should that antigen be encountered again.
Written By : Alexander Maness, United States (M.S. in Biotechnology)
Edited by: Rajesh Bihani ( Find me on Google+ )