Type 2 Immune Deviation Has Differential Effects on Alloreactive CD4+ and CD8+ T Cells

Allograft rejection has been associated with detection of the type 1 lymphokines, IFN-gamma and IL-2. The role of type 2 cytokines (IL-4 and IL-5) remains controversial, as is whether alloreactive CD4+ and CD8+ T cells behave similarly when exposed to type 2 cytokine-enhancing manipulations. We studied the characteristics of alloreactive CD4+ and CD8+ T cells before and after type 2 immune deviation induced by IL-4 plus anti-IFN-gamma Ab. Alloreactive T cells from naive mice were low in frequency, produced only IL-2, and were predominantly CD4+, while alloreactive T cells from allograft-primed mice were high in frequency, produced IFN-gamma, IL-2, and IL-4, and were predominantly CD8+. Type 2 immune deviation of allospecific CD4+ T cells resulted in IL-4 and IL-5 production without IFN-gamma, consistent with unipolar type 2 immunity. These T cells mediated delayed-type hypersensitivity, but not cytotoxicity. Under identical type 2 cytokine-inducing conditions, allospecific CD8+ T cells were primed to become IL-4, IL-5, and IFN-gamma producers, and exhibited cytotoxicity, but not classic delayed-type hypersensitivity. Adoptive transfer of either cell population into SCID recipients of allogeneic skin resulted in graft rejection, with stable allospecific type 2 cytokine production in vivo. Adoptive transfer of the IL-4/IL-5-producing CD4+ T cells, but not the CD8+ T cells, induced a distinct histopathology characterized by marked eosinophilic infiltration of the skin. We conclude that type 2 immune deviation has differential effects on CD4+ and CD8+ T cells and results in emergence of alternate effector mechanisms capable of destroying allografts.