Delayed hypersensitivity responses to human IgG and methylated bovine serum albumin are regulated by different mechanisms.

We found marked differences in in vitro and in vivo delayed hypersensitivity (DH) responses to human IgG (human gamma-globulin, HGG) and methylated bovine serum albumin (MeBSA). Lymph node cells (LNC) from cyclophosphamide (CY) pretreated, antigen-adjuvant immunized mice exhibited increased HGG-induced and decreased MeBSA-induced proliferative responses in vitro compared with LNC from similarly immunized but non-CY-pretreated animals. These effects were antigen-specific. Further, treatment of CY-HGG-adjuvant immunized mice with aqueous (aq) HGG either before or after immunization markedly suppressed HGG-specific in vitro proliferation and in vivo DH responses. Therefore, induction of suppression by aqHGG did not appear to depend on CY-sensitive cells either as a possible source of suppressor cell precursors or as participants in the regulatory events. In contrast, in vivo DH reactivity to MeBSA was unaffected by administration of aqMeBSA either before or after mice were immunized with CY-MeBSA-adjuvant. Our results suggest that DH responses to HGG and MeBSA are regulated by distinct mechanisms which influence the induction and the development of sensitivity.