REVERSAL OF GALLIUM ARSENIDE-INDUCED SUPPRESSION OF THE ANTIBODY-FORMING CELL RESPONSE BY VEHICLE SUPERNATANTS .2. NATURE AND IDENTIFICATION OF REVERSING FACTORS

Previous studies have demonstrated that several immunological events w hich are T cell mediated are significantly suppressed by a single expo sure to gallium arsenide (GaAs). In addition, in the in vitro-generate d antibody-forming cell (AFC) response supernatants from vehicle (VH) cultures were able to time-dependently reverse suppression induced by either in vivo (200 mg/kg) or in vitro (50 muM) exposure to GaAs. The present studies were designed to determine the nature and identificati on of the reversing factors present in VH supernatants. VH supernatant s (25-100%) were able to dose-dependently reverse suppression of the A FC response (from 45% suppression to 48% enhancement of the VH respons e) induced by GaAs exposure (200 mg/kg). Concentration of 24-hr VH sup ernatants and treatment with proteinases revealed that the reversing f actors were protein in nature with a molecular weight between 5,000 an d 50,000 Da. This molecular weight range encompasses many of the lymph okines known to be necessary for the generation of an immune response. In antibody cultures exposed either in vivo or in vitro to VH or GaAs , HT-2 bioassay and antigen capture enzyme-linked immunosorbent assays demonstrated that GaAs exposure alters production of interleukin (IL) -2, IL-4, IL-5 and IL-6. Interestingly, the alterations in lymphokine production differed between the exposure regimes. Direct addition of I L-2 to antibody cultures resulted in a dose-dependent (6.25-50 ng/ml) reversal of GaAs-induced suppression (in vivo exposure) and was also d ependent on the concentration of GaAs (50-200 mg/kg). IL-4 suppressed the VH AFC response and failed to reverse GaAs suppression. This VH su ppression was a result of a class switch from immunoglobulin M to immu noglobulin G1. Both IL-5 and IL-6 were able to reverse GaAs-induced su ppression, but these effects were not dose related. Anti-IL-5 antibody had no effect on the VH AFC response or the GaAs-induced immunosuppre ssion. In summary, these data indicate that the factors in VH supernat ants which reverse GaAs immunosuppression are protein in nature with m olecular weights between 5,000 and 50,000 Da. GaAs exposure altered pr oduction of all lymphokines evaluated; however, it would appear from t hese and previous data that IL-2 is a primary target for GaAs after in vivo exposure.