genes play an important role, they compose only a part of the immune system. Certain
Ir genes may code for cellular receptors for antigen and others may control mediator
secretion. Thus, the system controls not only have the ability to respond to antigens but
also to control the level and duration of the response.
Section II. HLA COMPLEX
a. The HLA complex is a region on chromosome 6 that codes for three
functionally different proteins: those that regulate the immune response, those that
determine the acceptance or rejection of transplanted tissues between individuals within
that species, and those that are a part of the complement system (Figure 4-1). The two
MHC systems that have been most extensively characterized are the H-2 system in the
mouse and the HLA (human leukocyte antigen) system in man. The MHC of mice has
provided information for the understanding of the human MHC.
b. In 1975, the World Health Organization established a nomenclature
committee for the human MHC system. HLA designates the region on chromosome 6
that carries the MHC gene segment. A letter after the HLA, such as HLA-D, refers to a
gene locus. International exchanges of typing reagents are organized every two to four
years by International Histocompatibility Workshops for HLA Genetics that engaged in
studying the genetics and serologic behavior of these proteins. These scientists
frequently reassign the position of a certain antigen (specificity) that in turn alters the
number of antigens (specificities) within the A, B, or other locus.