The response of BB diabetes-prone (DP) and W-line non-diabetes-prone rats to the T-cell mitogen concanavalin A (ConA) was measured. The W line was a good responder to ConA, whereas the DP was relatively unresponsive. This unresponsiveness could not be reversed with exogenous interleukin 2 (IL-2). The response of DP rats was enhanced by removing adherent cells. To directly test the response of BB T-cells, they were isolated by flow sorting. These experiments demonstrated that BB T-cells could mount a normal ConA response. The normal function of isolated BB T-cells suggested that they were under suppression. Suppressor activity could not be found in the 0X8+ population but was found in the DP-adherent cell population. Adherent cells from the W line were not suppressive at the concentrations used. These results showed that the decreased mitogen responsiveness of BB T-cells was not due to an intrinsic T-cell abnormality but was due, in part, to suppression by adherent cells.

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