Selective expression of separate I-region loci in functionally different lymphocyte subpopulations.

Determinants controlled by separate loci mapping in the I region of the H-2 gene complex are selectively expressed on subpopulations of lymphocytes which play different roles in generating humoral responses. The Ia-4 locus, which marks a new I subregion, designated I-J, controls determinants found on allotype suppressor and normal (nonsuppressed) T lymphocytes. These determinants are not present on helper T lymphocytes or B lymphocytes. In contrast, the Ia-1 locus, which marks the I-A subregion, controls determinants present on B lymphocytes but not on suppressor or helper T lymphocytes. Another locus (subregion not known) controls determinants which distinguish helper T lymphocytes from suppressor T lymphocytes. Such selective expression suggests that the products of these loci may plan an integral role in lymphocyte interactions.