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

We evaluated the importance of IL-2 and IL-6 in primary antigen-induced proliferation of lymph node cells (LNC) and the induction of contact hypersensitivity (CH). These responses were examined in cytokine-deficient mice following application of the contact sensitizer, oxazolone (OX). Proliferation and induction of IL-6 by LNC from IL-2-deficient (IL-2(-/-)) mice were reduced by approximately 95 %, relative to the proliferation of LNC from IL-2(+/+) mice, although induction and elicitation of CH responses was not significantly affected. In contrast, the proliferation of LNC from sensitized IL-6(- /-) mice was reduced by approximately 50% and the CH response was significantly reduced, relative to responses of IL-6(+/+) mice. Although nonspecific inflammatory responses induced by croton oil were similar in IL-6(+/+) and IL-6(-/-) mice, both the acute inflammatory response to OX and the second phase of the inflammatory response were significantly reduced. Thus IL-2 and IL-6 play a significant role in the total proliferative response of LNC following primary contact sensitization. However, the proliferation they promote is not critical for priming the antigen-specific effector cells responsible 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.