Cytokine production by CD4+ and CD8+ T cells in mice following primary exposure to chemical allergens: evidence for functional differentiation of T lymphocytes in vivo.

It has been demonstrated previously that repeated exposure of mice to chemical allergens of different types results in the development of qualitatively divergent immune responses characterized by the production by draining lymph node cells (LNC) of distinct cytokine patterns. Chronic exposure of mice to contact allergens, such as 2,4-dinitrochlorobenzene (DNCB), resulted in the secretion by LNC of low or undetectable levels of interleukins 4 and 10 (IL-4 and IL-10), but comparatively high levels of interferon gamma (IFN-gamma); the latter cytokine being produced by both CD4+ and CD8+ cells. In contrast, chronic exposure of mice to trimellitic anhydride (TMA), a respiratory allergen associated in humans with occupational asthma, induced instead the production by LNC of relatively high concentrations of IL-4 and IL-10, but little IFN-gamma. The low levels of IFN-gamma secretion which were provoked by treatment with TMA were shown to derive from CD8+ cells exclusively. In the present investigations we have sought to determine whether the polarized responses observed following repeated exposure to these chemical allergens are reflected by cytokine secretion patterns provoked by primary exposure. To this end, mice of BALB/c strain were exposed epicutaneously daily for 3 consecutive days to concentrations of DNCB and TMA (1 and 10%, respectively), or to oxazolone, another contact allergen (0.25%), that resulted in substantial proliferative activity in draining lymph nodes. The production by draining LNC of IFN-gamma and of mitogen-inducible IL-4 was measured by enzyme-linked immunosorbent assay and the relative contribution of CD4+ and CD8+ cells to the patterns of cytokine secretion observed was analyzed using both positive and negative selection methods. It was found that primary exposure to DNCB, oxazolone and TMA each resulted in the production by LNC of both IFN-gamma and IL-4. Selective depletion of, or enrichment for, CD4+ and CD8+ cells revealed that only CD4+ cells elaborated mitogen-inducible IL-4. Depletion of neither CD4+ nor CD8+ cells compromised the production by TMA- or DNCB-activated LNC of IFN-gamma, although positively selected CD8+ cells were considerably less able than CD4+ cells to elaborate this cytokine, presumably secondary to a lack of appropriate accessory cells. Taken together the results demonstrate that early during immune responses to DNCB or oxazolone and TMA there is no evidence for the selectivity of cytokine secretion patterns that characterizes responses following more chronic exposure. Moreover, it is clear that exposure to TMA initially induces the production of IFN-gamma by both CD4+ and CD8+ cells, whereas after more chronic treatment the secretion of this cytokine is a function of CD8+ cells exclusively. Collectively, these results indicate that the polarized responses that develop in mice following chronic exposure to different classes of chemical allergen are not reflected by the characteristics of primary immune responses. As such the development of qualitatively divergent immune responses to chemical allergens provides a paradigm for the evolution of differentiated T cell function with time and/or with antigen exposure.