AN IN VIVO AND IN VITRO STUDY OF THE CYCLOPHOSPHAMIDE‐INDUCED ENHANCEMENT OF CONTACT SENSITIVITY TO 2,4‐DINITRO‐1‐CHLOROBENZENE (DNCB)

Abstract

ABSTRACT Enhancement of DNCB contact sensitivity (CS) reactions by cyclophosphamide (Cy) was observed in guinea pigs sensitized by painting or footpad injection of Freund's incomplete adjuvant, in which immunologic suppression of CS had been induced, but not in animals sensitized by footpad injection of Freund's complete adjuvant. The latter developed markedly strong CS reactions. The effects of Cy on in vivo skin reactions and on in vitro endogenous and antigen‐induced DNA synthesis by the draining lymph node cells in animals sensitized topically with DNCB were studied on various days after sensitization. Cy treatment 3 days before sensitization augmented CS reactions. This augmentative effect was found from day 5 to day 21. Cy treatment enhanced in vitro antigen‐induced DNA synthesis as well as endogenous DNA synthesis by the draining lymph node cells. Cy‐sensitive cells and their progeny may be involved in suppression of the in vitro specific stimulation of the primed cells as well as endogenous cell proliferation for priming. The effect of DNCB‐sensitization on the in vitro concanavalin A (ConA) dose‐response of the spleen cells and lymph node cells was studied. By day 7 after sensitization, the stimulation of the spleen cells by low doses of ConA had decreased, but the responses to high doses of mitogen had increased. This bidirectional effect of DNCB‐sensitization on ConA responses was discussed.