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

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Abstract
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 A1 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 A1 supernatant with SRBC removed all activity, while several other species of red cells failed to do so. The suppressor factor present in A1 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. Al cells carried H-2 and Thy-1 alleles of both parental cells and formed rosettes with SRBC.