Regulation of T-cell activation and T-cell growth factor (TCGF) production by hydrogen peroxide

Abstract

Activated macrophages are known to release a variety of immunoregulatory substances including the low-molecular-weight substances hydrogen peroxide and lactate. We report here that lactate but not hydrogen peroxide is capable of supporting a substantial production of T-cell growth factor (TCGF) in cultures of accessory cell-depleted splenic T-cell populations after stimulation with concanavalin A. Hydrogen peroxide and its biosynthetic precursor superoxide anion (O − 2) mediate, however, a strong augmentation of the TCGF production by accessory cell-depleted T-cell populations in the presence of lactate. Lactate inhibits the incorporation of [ 3H]thymidine in short-term cultures (18–26 hr) of accessory cell-depleted T cells. This confirms the rule that (optimal) production of T-cell growth factor requires a growth inhibitory signal. Concentrations of hydrogen peroxide which augment TCGF production most effectively (i.e., 1 × 10 −5 M) do not inhibit the incorporation of [ 3H]thymidine; and higher concentrations (3 × 10 −5−1 × 10 −4 M) of hydrogen peroxide inhibit both the production of TCGF and the incorporation of [ 3H]thymidine. In agreement with the augmenting effect of hydrogen peroxide on TCGF production, it was observed that the proliferative response in mixed lymphocyte cultures is suppressed by catalase and augmented by 1 × 10 −5 M H 2O 2. Proliferative and cytotoxic responses in mixed lymphocyte cultures with an external source of interleukin 2 (IL-2) in contrast, are not augmented by 1 × 10 −5 M H 2O 2. The relatively high concentration of 1 × 10 −4 M hydrogen peroxide was found to inhibit the proliferative responses in mixed lymphocyte cultures with or without external IL-2 but not the cytotoxic response in the presence of IL-2. This indicates that CTL precursor cells may be relatively resistant against H 2O 2.