Immune system

From ArticleWorld

The immune system is the body system concerned with the cellular defense against any foreign substance or microorganism. The immune system is also active in destroying cancer cells in the body.

Components

Several organs and cell types are involved with the immune system. The bone marrow is the source of the cells that participate in immunity. These include phagocytic cells that can essentially “eat” other cells. Among them are neutrophils, macrophages and dendritic cells.

The bone marrow also creates lymphocytes of two major types. B lymphocytes make antibodies against viruses and other sources of foreign antigens (markers) that mark foreign cells for killing. T lymphocytes are processed by the thymus before going on to become killer cells, helper cells or other cells that regulate cell-mediated immunity.

Types

There are two broadly-defined types of immunity. The first is called innate immunity or that part of the immune system that continually fights off foreign agents without the necessity of antibodies. Considered the first line of defense, innate immunity involves the presence of receptors that recognize a particular agent as foreign or not foreign to the host. Phagocytes can directly kill whatever pathogen is considered foreign to the host.

The adaptive or acquired immunity involves the making of antibodies by B-cells against a protein or other molecule on the surface of a pathogen. When the antibody is produced in sufficient numbers, the pathogenic cells are tagged with the antibodies. Phagocytic cells, particularly cytotoxic T-lymphocytes, destroy the antibody-tagged foreign pathogen.

Adaptive immunity involves specific immune responses to specific antigens that an individual contacts with. This kind of immunity is generally lifelong as the individual retains the capability to recreate a sufficient immune response to a pathogen many years after initial exposure.

Disorders

There are many genetic conditions that can result in a less than adequate immune system. An infection with the human immunodeficiency virus (HIV) can result in AIDS, an immune deficiency syndrome that primarily affects an individual’s T cell function.