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The immunoregulatory role of bone marrow. III. Further characterization of the suppressor cell and its mode of action.

In vitro primary antibody responses of spleen cells can be suppressed in a dose-dependent manner by the addition of bond marrow cells (BMC). This suppression was not abrogated by treatment of BMC with anti-Thy 1, anti-Lyt nor with anti-I-J antisera and complement. Furthermore, preculture of BMC with the synthetic thymic pentapeptide (TP5) or Soluble Thymic Factor (STF) before anti-Thy-1 treatment was similarly ineffective in removing the suppressor cell activity. Similarly, treatment of BMC with polyvalent anti-immunoglobulin serum or anti-Ia antiserum and complement failed to remove the suppressor activity. However, preparations of anti-H-2 and anti-stem-cell antisera were capable of significantly decreasing the suppressive ability of BMC. BMC were also shown to be capable of suppressing antibody responses induced by the polyclonal activators dextran sulphate (DxS), lipopolysaccharide (LPS) and purified protein derivative from tubercle bacilli (PPD). The non-specificity of this suppressor coupled with the absence of well-defined antigen on its surface may suggest that this cell represents a basic level of immune regulation.