The role of histocompatibility gene products in lymphocyte triggering and differentiation.

Studies performed both in vivo and in vitro have demonstrated that genetic restrictions exist in the development of optimal cell-cell interactions in the immune system. Thus, in mice, the presence or absence of gene identities in the I region of the H-2 complex determines the capacity of lymphoid cells to interact. These cell interaction or CI genes appear to code for cell surface molecules integrally involved in regulatory cell interactions. Analysis of biologically active thymus-derived (T) cell factors capable of regulating differentiation events in other lymphoid cells indicates that such factors are around 40,000-50,000 daltons in mass, bear determinants coded for by I region genes, and consist of two covalently or noncovalently linked components--a heavy glycoprotein of around 40,000 daltons and a lighter protein of around 12,000 daltons. Preliminary evidence suggests that the latter component may be beta2-microglobulin.