The host or patient has physical barriers, such as intact skin and ciliated epithelial cells, and chemical barriers, such as oils produced by the sebaceous glands and lysozyme found in tears and saliva, to prevent infections by foreign organisms. In addition, natural immunity, which is not specific, causes chemotaxis, the process by which phagocytes engulf organisms that enter the host and produce substances that attract c 'hite blood cells to the site of infection. Acquired immunity is the specific response of the host to an infecting organism.
The human specific immune responses are simpli-stically divided into the following two categories: cellmediated and antibody-mediated.
Cell-mediated immune responses are carried out by special lymphocytes of the T (thymus-derived) class. T cells proliferate and differentiate into various effector T cells, including killer and helper cells. Killer cells, also known as cytotoxic T lymphocytes, specifically attack and kill microorganisms or host cells damaged or infected by these pathogens. Helper cells promote the maturation of B cells by producing activator cytokines that induce the B cells to produce antibodies and attach to and kill invading organisms. Although diagnosis of certain diseases may be aided by measuring the cell-mediated immune response to the pathogen, such tests entail skin tests performed by physicians or in vitro cell function assays performed by specially trained immunologists. These tests are usually not within the repertoire of clinical microbiology laboratories.
Antibody-mediated immune responses are those produced by specific proteins generated by lymphocytes of the B (bone marrow-derived) class. Because these proteins exhibit immunologic function and because they fold into a globular structure in the active state, they are also called immunoglobulins.
Antibodies are either secreted into the blood or lymphatic fluid (and sometimes other body fluids) by the B lymphocytes, or they remain attached to the surface of the lymphocyte or other cells. Because the cells involved in this category of immune response chiefly circulate in the blood, this type of immunity is also called humoral immunity. For purposes of determining whether an antibody has been produced against a particular infectious agent by a patient, the patient's serum (or occasionally the plasma) is tested for the presence of the antibody. The study of the diagnosis of disease by measuring antibody levels in serum is called serology.
Was this article helpful?