The human immune system protects the body from foreign objects such as microorganisms. It is made of several cells that are spread throughout the body, each playing different roles and moving through the body, as needed.
There are two main types of blood cells. The most common are red blood cells or red blood cells, which carry oxygen to the body tissues and remove carbon dioxide. The other group is the white blood cells, or leukocytes. These are the immune cells.
Some white blood cells recognize specific foreign bodies so that the body has been exposed in the past. These immune cells are called lymphocytes. Other white blood cells are non-specific and can attack a range of different foreign organisms: these include neutrophils, eosinophils and natural killer cells.
There are two different types of lymphocytes. B lymphocytes (sometimes just called B-cells) produce antibodies. An antibody is a protein that can block a particular role in a given foreign body. When this happens, the antibody signals to other immune cells to attack the organism.
T lymphocytes (sometimes just called T-cells) are called different names depending on the molecules on their surface. CD4 cells(Also known as T lymphocytes CD4 and T-helper cells) play a coordinating role in the immune system. They help B-lymphocytes identify foreign organisms (which they produce antibodies against). They also secrete substances that activate CD8 cells to reproduce. CD4 cells also activate macrophages (see below) to kill certain organisms, including many of the subsequent disease AIDS, opportunistic diseases. When CD4 cells are destroyed by HIV, all these parts of the immune system are stopped. CD8 cells (also known as T-lymphocytes or cytotoxic T cells CD8) are connected to the body abnormal cells, including cells which have been infected by viruses, and kill them.
Other immune cells
Natural killer (NK) cells attack tumor cells and virus-infected cells in a manner similar to the lymphocytes. But while each lymphocyte can only recognize and attack cells infected by one specific virus, natural killer cells can attack a wider range.
Eosinophils attack organisms that are too big to be eaten by a single phagocyte, like worms.
Phagocytes are cells that attack and destroy foreign cells, choking them. There are two main types of phagocytes.
- Macrophages move in blood and body tissues, killing organisms that can cause diseases related to AIDS and virus-infected cells.
- Neutrophils leave the bloodstream and go to tissues where infection or inflammation is developing. These are mainly bacteria and fungi.