Analyses of Ia restriction specificity of helper T cells in H-2 subregion compatible bone marrow chimera in mice.

Using irradiation bone marrow chimeras which had partial compatibility in H-2 subregions between donor and recipient mice, we found that H-2I matching was sufficient for the chimeras to generate anti-sheep erythrocyte plaque-forming cell (PFC) responses. In such chimeras, T cells appeared to encounter appropriate partner cells bearing the same Ia antigens as those which they had learned to recognize as self in the recipient micro-environment. Furthermore, the PFC number seen in I-A compatible chimeras was only about half of that seen in I-A, I-E compatible chimeras, suggesting the existence of two independent subpopulations of helper T cells. When incompatibility of donor and recipient mice existed on the left side of the H-2I region, the responses were very weak. However, even in such chimeras, marked responses were observed for both IgM and IgG type PFC following a sufficient period after immunization. This observation appears to indicate the existence of a minor subpopulation of helper T cells which can expand and interact effectively with antigen presenting cells of donor type.