Elimination of environmental viruses by cesarean derivation of the University of Massachusetts colony of BB/Wor rats increased the frequency and accelerated the tempo of spontaneous diabetes among diabetes-prone (DP) rats. In contrast, the viral-antibody–free (VAF) environment did not alter the resistance of pre-VAF diabetes-resistant (DR) rats to spontaneous and RT6+ T-lymphocyte–depletion–induced diabetes. Pre-VAF and VAF rats have essentially the same lymphocyte subsets, and VAF-DP rats are susceptible to the adoptive transfer of diabetes and to the diabetes-accelerating effects of polyinosinic-polycytidylic acid injections. These results suggest that the presence of environmental viral pathogens may act to inhibit effector cell function in lymphopenic DP rats while enhancing effector cell activity in nonlymphopenic DR rats.

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