In Vitro Synthesis of IL-4 by Human CD4+ T Cells Requires Repeated Antigenic Stimulation

Although Th2 helper cell clones produce IL-4 and IL-5, CD4+ T cells taken fresh from lymphoid organs of mice produce IL-2 and some IFN-γ, but not IL-4 or IL-5. The exact parameters that enhance the synthesis or IL-4, IL-5, and particularly IL-10 from resting antigen-specific CD4+ T cells is not yet clear. We therefore examined the kinetics of, and the parameters that affect, the development of IL-4, IL-5, and IL-10 production in bulk populations of antigen-specific human CD4+ T cells. We demonstrated that in vitro stimulation of human peripheral blood lymphocytes with antigen (tetanus toxoid or a vital antigen, Varicella zoster) for several days resulted in the production of IL-2 and IFN-γ, but little or no IL-4 or IL-5. This cytokine profile was observed even when CD4+ T cells from allergic donors were stimulated once in vitro with allergen (rye grass pollen, Lolium perenne I, or dust mite allergen. Dermatophagoides farinae). The observed cytokine profile reflected that of the vast majority of antigen-specific T cells, since we studied the response of bulk populations of CD4+ T cells lather than that of a "selected" number of antigenspecific T cell clones. Furthermore, we observed that human CD4+ T cells from either allergic or nonallergic individuals failed to produce significant quantities of IL-4, IL-5, or IL-10 even after several rounds of stimulation with soluble protein (nonallergen) antigens such as tetanus toxoid or Var. z. However, large quantities of these cytokines were produced when stimulation or the T cells occurred in the presence of rIL-4, but only after two stimulations in vitro with antigen over a period of greater than 7 days. In addition, substantial quantities or IL-4, IL-5, and IL-10 were produced by CD4+ T cells from allergic subjects in the absence of exogenous IL-4, but only after two stimulations in vitro with allergens such as rye grass pollen or dust mite allergen. These results indicate that the development of IL-4 and IL-5 synthesis occurs in peripheral blood CD4+ T cells in a stepwise fashion, first with the production of IL-2 and IFN-γ, and later with the production of IL-4 and IL-5. In addition, these studies are the first to demonstrate that IL-4 upregulates the synthesis of IL-10 in humans and indicate that the synthesis of IL-4, IL-5, and of IL-10 are coordinately regulated in a manner different from that of IL-2 and IFN-γ.