ABSTRACT
The acquired immune response to pathogens depends on functional T and B lymphocytes in the primary and secondary lymphoid organs. T lymphocytes develop in the thymus, where they are selected for lack of strong reactivity with self-antigens, and migrate to the same secondary lymph organs as the B lymphocytes. The process of maturation of both cell types involves the synthesis of receptor molecules that are critical for future recognition of antigens. These receptor molecules are synthesized from segments of DNA. The enzymes responsible for the process include a DNA-dependent protein kinase, which repairs the break in the DNA strand and allows the new receptor to be created from an intact DNA strand. Severe combined immunodeficiency occurs in humans. A variety of syndromes have been described, each caused by a different mutation. The most common of these is the X-linked severe combined immunodeficiency.
