Abstract
The H-2 system is a complex of at least ten loci carried by chromosome 17 of the mouse. The loci can be divided into three or four functional classes concerned with the control and execution of immune response. The different classes are in some specific way involved in: 1. differentiation of bone-marrow derived (B) lymphocytes, leading to the production of humoral antibodies detectable by serological methods; 2. differentiation of thymus-derived (T) lymphocytes, leading to the production of killer cells capable of specifically attacking relevant targets; 3. regulation of immune response, both humoral and cellular (this response can be either enhanced or suppressed); 4. biosynthesis and activation of components of the complement system. On the same chromosome as the H-2 is the T/t complex, which controls embryonic and spermatozoal differentiation. An interesting relation between H-2 and T/t might exist between the complexes of loci.