Other lymphocytes, called T lymphocytes, or T cells, mature in the thymus, a small glandular organ located behind the breastbone. Some T lymphocytes, called cytotoxic (cell-poisoning) or killer T lymphocytes, generate cell-mediated immune responses, directly destroying cells that have specific antigens on their surface that are recognized by the killer T cells. Helper T lymphocytes, a second kind of T lymphocyte, regulate the immune system by controlling the strength and quality of all immune responses.
Most contact between antigens and lymphocytes occurs in the lymphoid organs—the lymph nodes, spleen, and tonsils, as well as specialized areas of the intestine and lungs (see Lymphatic System). Mature lymphocytes constantly travel through the blood to the lymphoid organs and then back to the blood again. This recirculation ensures that the body is continuously monitored for invading substances.
Adaptive immune responses are actually reactions of the immune system to structures on the surface of the invading organism called antigens. There are two types of adaptive immune responses: humoral and cell mediated. During humoral immune responses, proteins called antibodies, which can stick to and destroy antigens, appear in the blood and other body fluids. Humoral immune responses resist invaders that act outside of cells, such as bacteria and toxins (poisonous substances produced by living organisms). Humoral immune responses can also prevent viruses from entering cells.
Humoral are, I suppose, white blood cells made in the bone marrow. They eat bacteria. Cell-mediated immunity is when cells give off chemicals (like histamine) to kill the foreign things bugging our bodies.
The three major types of lymphocyte are T cells, B cells and natural killer (NK) cells.
T cells belong to a group of white blood cells known as lymphocytes and play a central role in cell-mediated immunity. They can be distinguished from other lymphocyte types, such as B cells and NK cells by the presence of a special receptor on their cell surface that is called the T cell receptor (TCR). The abbreviation “T”, in T cell, stands for thymus since it is the principal organ for their development.
B cells are lymphocytes that play a large role in the humoral immune response as opposed to the cell-mediated immune response that is governed by T cells. The abbreviation “B” comes from bursa of Fabricius that is an organ in birds in which avian B cells mature. The principal function of B cells is to make antibodies against soluble antigens. B cells are an essential component of the adaptive immune system.
Natural killer (NK) cells are a form of cytotoxic lymphocyte which constitute a major component of the innate immune system. NK cells play a major role in the host-rejection of both tumors and virally infected cells. They were named “natural killer” because of the initial notion that they do not require activation in order to kill cells which are “missing self” recognition (“missing-self” recognition is a term used to describe cells with low levels of MHC (major histocompatibility complex) class I cell surface marker molecules — a situation which could arise due to viral infection, or in tumors under strong selection pressure of killer T cells).
Cell-mediated immunity, also known as delayed-type hypersensitivity (DTH) or Type IV Hypersensitivity, is an immune response that does not involve antibodies but rather involves the activation of macrophages, natural killer cells (NK), antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen. Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells. Cellular immunity protects the body by:
activating antigen-specific cytotoxic T-lymphocytes that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens;
activating macrophages and natural killer cells, enabling them to destroy intracellular pathogens; and
stimulating cells to secrete a variety of cytokines that influence the function of other cells involved in adaptive immune responses and innate immune responses.
Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria. It also plays a major role in transplant rejection.
The Humoral Immune Response (HIR) is the aspect of immunity that is mediated by secreted antibodies, produced in the cells of the B lymphocyte lineage (B cell). Secreted antibodies bind to antigens on the surfaces of invading microbes (such as viruses or bacteria), which flags them for destruction. Humoral immunity is called as such, because it involves substances found in the humours, or body fluids.
The study of the molecular and cellular components that comprise the immune system, including their function and interaction, is the central science of immunology. The immune system is divided into a more primitive innate immune system, and acquired or adaptive immune system of vertebrates, the latter of which is further divided into humoral and cellular components.
Humoral immunity refers to antibody production, and the accessory processes that accompany it, including: Th2 activation and cytokine production, germinal center formation and isotype switching, affinity maturation and memory cell generation. It also refers to the effector functions of antibody, which include pathogen and toxin neutralization, classical complement activation, and opsonin promotion of phagocytosis and pathogen elimination.
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