Deficiency of IL-2 or IL-6 reduces lymphocyte proliferation, but only IL-6deficiency decreases the contact hypersensitivity response

We evaluated the importance of IL-2 and IL-6 in primary antigen-induced pro liferation of lymph node cells (LNC) and the induction of contact hypersens itivity (CH). These responses were examined in cytokine-deficient mice foll owing application of the contact sensitizer, oxazolone (OX). Proliferation and induction of IL-6 by LNC from IL-2-deficient (IL-2(-/-)) mice were redu ced by approximately 95 %, relative to the proliferation of LNC from IL-2(/+) mice, although induction and elicitation of CH responses was not signif icantly affected. In contrast, the proliferation of LNC from sensitized IL- 6(-/-) mice was reduced by approximately 50 % and the CH response was signi ficantly reduced, relative to responses of IL-6(+/+) mice. Although nonspec ific inflammatory responses induced by croton oil were similar in IL-6(+/+) and IL-6(-/-) mice, both the acute inflammatory response to OX and the sec ond phase of the inflammatory response were significantly reduced. Thus IL- 2 and IL-6 play a significant role in the total proliferative response of L NC following primary contact sensitization. However, the proliferation they promote is not critical for priming the antigen-specific effector cells re sponsible for eliciting CH responses and IL-6 appears to be more important for expression of the later phases of acute inflammation and the CH induced by OX.