Low-dose X-irradiation and 4-hydroperoxycyclophosphamide distinguishes three Lyt-1+ lymph node T-cell subtypes that respond to specific antigen in vitro.

We investigated whether preculture exposure to low-dose X-irradiation and culture treatment with 4-hydroperoxycyclophosphamide (4-HPCY), a synthetic derivative of cyclophosphamide (CY), might distinguish subtypes of thymic-dependent (T) lymphocytes that respond to specific antigen in vitro. Lymph node (LN) cells were obtained from mice pretreated with CY and immunized with aggregated (A) human IgG (HGG) in Freund's complete adjuvant (CFA), and proliferation was assessed by incorporation of tritiated thymidine. Primed LN cells were untreated or exposed to low-dose irradiation before being cultured in medium alone and in medium containing 4-HPCY. The results show that these agents (irradiation and 4-HPCY) distinguished, in a dose-dependent manner, subtypes of T-cells which contribute to the specific antigen-stimulated proliferative response in vitro. For LN T-cells and LN Lyt-1+ T-cells, 20-25 rads and 1.0 microM 4-HPCY inactivated non-overlapping cell subtypes that respectively accounted for 26% and 28% of the response to HGG. The remaining 46% of HGG-responding cells were not affected by either agent. Although similar cell subtypes were discerned in unseparated LN cells, it required use of higher agent-doses. Cell cycle analysis revealed that treatment with irradiation, 4-HPCY, and the combination (both agents) caused S-phase arrest of 29%, 30%, and 55% of HGG-responding cells, respectively. Thus, identification of these cell subtypes could not be attributed to agent-mediated inactivation of HGG-responding cells that might be in exclusively different phases of the cell cycle.