Immunological activity of a T hybrid line. I. Production of an H-2-related suppressor factor with specificity for sheep red blood cells.

T lymphocyte hybrid lines have been produced by fusion of the thymoma BW 5147 with spleen cells of C57BL/10 mice primed to sheep red blood cells (SRBC). The supernatant (culture fluid) of a T hybrid designated A 1 was able to suppress the primary (IgM) and secondary (IgM and IgG) antibody responses to SRBC in vitro. The suppressive activity of supernatants could be titrated to 50% end points at final dilutions of up to 1 : 270. The suppression affected only SRBC and haptens coupled to SRBC, except when used at high concentration when some nonspecific suppression was observed. Absorption of the A 1 supernatant with SRBC removed all activity, while several other species of red cells failed to do so. The suppressor factor present in A 1 supernatant was not removed by anti-Ig adsorbents, but was removed by anti-H-2 antibodies reacting specifically with the haplotype of the spleen cells used in the fusion (H-2b). The cellular target of action of the factor was apparently a B cell, based on absorption with different cell populations. No genetic restrictions in the activity of the factor were found. A 1 cells carried H-2 and Thy-1 alleles of both parental cells and formed rosettes with SRBC.