A subset of CD8+ T cells from allergic patients produce IL-4 and stimulate IgE production in vitro

Background and Objective A subset of IL-4 producing CD8⁺ T cells was recently identified in HIV patients. Based on these findings we examined whether IL-4 producing CD8⁺ T cells would also be present in allergic patients and what would be the functional relevance of this T-cell population. Methods We investigated the role of CD8⁺ T cells in IgE production of allergic diseases by analysing the cytokine profile of individual CD4⁺ and CD8⁺ T cells. Results In allergic patients about twice as many CD4⁺ T cells and six times as many CD8⁺ T cells produced IL-4 as in non-allergic controls. In contrast the frequency of IFNγ⁺ T-cell subsets did not significantly differ between the allergic and non-allergic individuals. The frequency of 1L4⁺CD8⁺ T cells correlated with the level of serum IgE. Coculture experiments with T cells or purified CD8⁺ T cells together with autologous B cells indicated that CD8⁺ T cells enhanced IgE in vitro, but not IgM production, even when they were physically separated from B cells. This effect could be partially blocked by addition of an IL-4 binding protein, a soluble IL-4 receptor indicating that lL-4 is involved in CD8⁺ T-cell mediated IgE production. Conclusions These data indicate a positive role of IL-4 secreting CD8⁺ T cells in IgE regulation in allergic patients.