The body’s immune system is composed of various types of cells that can find and eliminate viruses and other infections. Immune cells called lymphocytes have receptors that can detect the Cluster of Differentiation (CD) protein on the surface of a cell, specifically CD8 in the case of one type, that represent what is inside the membrane. The CD8 lymphocytes, also called T-cells, can detect cells that are infected with a virus, and then release molecules that lead to their death. Sometimes the immune system eliminates these cells before more viruses are replicated and released into the body.
One type of white blood cell, Cytotoxic T-cell Lymphocytes (CTLs) typically pass between cells in the search for foreign materials. If CD8 lymphocytes recognize a peptide on a cell membrane called an antigen, it can trigger the release of signaling proteins called cytokines to put the immune system on alert. When infected cells and those that are otherwise dysfunctional are located, CD8 lymphocytes often release compounds that penetrate the cell membrane, enter the cell, and trigger a programmed cell death called apoptosis. Cell death can also be accomplished when proteins on the lymphocyte bind to the target surface and signal the right sequence of events.
The CD8 receptor is a glycoprotein that can be found in alpha and beta forms. Often located on the surface of T cells as well as natural killer cells, it typically protrudes from the cell membrane as a stalk structure, while a tail portion sits at the interior side. When activated by an antigen, the CD8 lymphocytes are usually tightly connected to the target cells from the interaction of the cluster of differentiation and major histocompatibility complex (MHC) molecules.
Receptors on the CD8 lymphocytes typically react with class I MHC molecules, which are found on most cells in the body. Another common receptor called CD4 usually interacts with class II molecules, which are often part of immune cells called macrophages and B cells. It is typically located on dendritic cells, or those that line parts of the intestine, lungs, or skin. These types are antigen presenting cells that often trigger inflammation when T-cells are activated.
Too many CD8 lymphocytes in the body can indicate a weakened immune system. A lower number, however, often suggests immunity could be hyperactive. They are classified as suppressor cells, so the health of the immune system can be evaluated by comparing the number of these to CD4 receptor-carrying B cells.