Differential requirement for accessory cells in polyclonal T-cell activation

Abstract

Highly purified rat la-negative (OX-6 −) and la-positive (OX-6 +) T cells were employed to examine the requirement for accessory cells (AC) and/or soluble factors in the activation of resting T cells with Con A, PHA, sodium periodate, or antigen. A variety of cells were employed as AC, including la-positive and la-negative macrophages (Mφ), γ-irradiated (2000 rad) or non-irradiated OX-6 − T cells and several la-negative adenovirus-transformed rat embryo fibroblast cell lines. Our results suggested that for the expression of IL-2 receptors (IL-2R) and proliferation of OX-6 − T cells in response to Con A, PHA, or antigen, there was an obligatory requirement for the presence of AC which could not be overcome by the addition of IL-1 and/or IL-2. Activation of OX-6 − T cells with antigen required the presence of Ia + AC, while activation with mitogens could be initiated with Ia − AC. Mφ were efficient in AC function in all responses tested, while the AC function of OX-6 + T cells (TAPC) proved discriminatory under different conditions. The optimal response to PHA required much higher concentrations of TAPC as AC than for the Con A response. TAPC failed to stimulate sodium periodate-treated T cells under any conditions tested. Furthermore, when TAPC were employed as AC, their antigen-presenting ability was radiosensitive, while their AC function for Con A and PHA was radioresistant. These results suggest that molecules involved in T cell-AC interactions may differ, depending on the source of AC and/or type of the proliferative stimulus provided to T cells. This data has been discussed in the context of T-cell activation.