The role of CD4+ vs CD8+ T cells in contact hypersensitivity (CHS) remains controversial. In this study, we used gene knockout (KO) mice deficient in CD4+ or CD8+ T cells to directly address this issue. Mice lacking either CD4+ or CD8+ T cells demonstrated depressed CHS responses to dinitrofluorobenzene and oxazolone compared with wild-type C57BL/6 mice. The depression of CHS was more significant in CD8 KO mice than in CD4 KO mice. Furthermore, in vivo depletion of either CD8+ T cells from CD4 KO mice or CD4+ T cells from CD8 KO mice virtually abolished CHS responses. Lymph node cells (LNCs) from hapten-sensitized CD4 and CD8 KO mice showed a decreased capacity for transferring CHS. In vitro depletion of either CD4+ T cells from CD8 KO LNCs or CD8+ T cells from CD4 KO LNCs resulted in a complete loss of CHS transfer. LNCs from CD4 and CD8 KO mice produced significant amounts of IFN-γ, indicating that both CD4+ and CD8+ T cells are able to secrete IFN-γ. LNCs from CD8, but not CD4, KO mice were able to produce IL-4 and IL-10, suggesting that IL-4 and IL-10 are mainly derived from CD4+ T cells. Intracellular cytokine staining of LNCs confirmed that IFN-γ-positive cells consisted of CD4+ (Th1) and CD8+ (type 1 cytotoxic T) T cells, whereas IL-10-positive cells were exclusively CD4+ (Th2) T cells. Collectively, these results suggest that both CD4+ Th1 and CD8+ type 1 cytotoxic T cells are crucial effector cells in CHS responses to dinitrofluorobenzene and oxazolone in C57BL/6 mice.

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To determine the role of CD4 molecules in the generation and regulation of contact hypersensitivity (CHS), we treated mice lacking the CD4 gene as a result of targeted disruption with dinitrofluorobenzene to induce CHS. The mutant mice lacking CD4 (CD4(-) mice) showed marked hyporesponsiveness in CHS compared with normal syngeneic C57BL/6 mice (38.3 +/-9.0% of normal at 24 h after the challenge assessed by net ear swelling; p < 0.025). CD4(-) mice had a larger CD4-8- double negative T-cell receptor alpha beta+ cell population in the lymph nodes than did normal mice, and the increase of this cell population was observed in CD4(-) mice after sensitization. Draining lymph node cells from sensitized normal mice restored the responsiveness in CD4(-) mice, but those from sensitized CD4(-) mice were less effective in restoring the CHS response in normal mice. Langerhans cell numbers were normal, and function, as assessed by the ability to present soluble hapten, was not impaired in CD4(-) mice. Skin cytokine profiles demonstrated an increase in interferon-gamma, interleukin-2, and interleukin-4 mRNA levels after challenge in normal mice, whereas this response was blunted in CD4(-) mice. CD4(-) mice also showed hyporesponsiveness in inflammatory reaction to irritant chemicals. These results suggest that the CD4 molecule is required for optimal induction of CHS as well as irritant contact dermatitis and may influence the development of CHS by modulating the cytokine profiles in the skin.

Interleukin-1 receptor antagonist (IL-1ra), a naturally occurring inhibitor of interleukin-1 (IL-1), blocks IL-1 binding to its receptors but has no agonistic activity. IL-1 is thought to play an important role in contact hypersensitivity (CHS), although the effects of exogenously administered IL-1 in CHS have been somewhat controversial. To clarify the role of IL-1 in CHS, we studied the effect of IL-1 receptor blockade using exogenous IL-1ra and evaluated these effects on CHS. We examined the in vivo effects of local administration of recombinant human IL-1ra in the murine CHS model. Local injection of IL-1ra to sensitized BALB/c mice just before challenge with dinitrofluorobenzene resulted in a significant reduction in the intensity of CHS responses, assessed by ear swelling. A dose-response study revealed that maximal inhibition of ear swelling (36% to 43%) was observed after intradermal injection of IL-1ra at doses of 10 to 100 micrograms/ear. This reduction in ear swelling in IL-1ra-injected ears consisted of less inflammatory cell infiltration and decreased edema in the dermis compared with controls. Suppression of CHS was observed when IL-1ra was applied in the 24-h interval preceding challenge with dinitrofluorobenzene, whereas no suppressive effect was observed when IL-1ra was applied 48 h before or after the challenge. Local administration of IL-1ra to naive mice 5 h before sensitization also suppressed CHS responses. However, IL-1ra injection did not suppress phenol-induced inflammation. These results suggest that IL-1ra is an effective inhibitor of both the sensitization and elicitation phases of CHS expression in mice, thus emphasizing the role of IL-1 as an immunologic potentiator of responses associated with CHS.

SUMMARYLangerhans' cells (LC) represent the major antigen-presenting cells within the epidermis. Following exposure of the skin to antigen, LC take up antigen, migrate into draining lymph nodes (DLN) and present processed antigen to T lymphocytes, thereby initiating an immune response. The molecular mechanisms responsible for LC migration remain unclear. Cytokines, in particular tumour necrosis factor-a (TNF-a) have been suggested to influence LC migration. There are two distinct membrane receptors for TNF-a, T N F receptor I (TNF-Rl, p55) and T N F receptor I1 (TNF-R2, p75), thought to be responsible for distinct TNF-a activities. It is believed that most of T N F biological activities are mediated via TNF-Rl. In order to examine the role of TNF-R1 signalling in LC migration, we utilized TNF-RI gene-targeted mutant mice. Following application of the hapten fluorescein isothiocyanate (FITC), FITC-bearing cells in DLN were examined by flow cytometry. A normal number of FITC+/Ia+ cells (LC) were found in DLN from TNF-R1-deficiency mice, suggesting that TNF-R1-dependent signalling is not crucial for LC migration. To investigate the possibility of signalling through TNF-R2, blocking studies using a neutralizing anti-TNF-a antibody were performed. The results revealed that anti-TNF-a antibody significantly inhibited LC accumulation in DLN in TNF-RI-deficient mice, thus suggesting that TNF-R2 signalling is involved in LC migration from skin to DLN and that murine LC express TNF-R2.