Early delayed‐type hypersensitivity eosinophil infiltrates depend on T helper 2 cytokines and interferon‐γ via CXCR3 chemokines

We investigated the role of T helper (Th)1‐ and Th2‐type cytokines in delayed‐type hypersensitivity to soluble protein antigens elicited early postimmunization. Mice were sensitized by intradermal injection without adjuvants, or subcutaneously with complete Freund's adjuvant, and subsequently ear challenged intradermally. As soon as day 3, antigen‐specific eosinophil‐rich responses were elicited in wild‐type mice, but not in T‐cell receptor‐α–/– mice without adjuvant. Draining lymph node T cells stimulated with antigen secreted interleukin (IL)‐4, IL‐5 and interferon‐γ (IFN‐γ). IFN‐γ‐dependent specific immunoglobulin G (IgG)2a and IL‐4‐dependent IgG1 were also generated. Delayed‐type hypersensitivity ear swelling and local eosinophil recruitment were decreased in IL‐5–/–, IL‐4–/– and signal transducer and activator of transcription‐6 (STAT‐6)–/– mice, and with anti‐IL‐4 treatment of wild‐type mice, suggesting Th2 mechanisms. Interestingly, responses were also decreased in IFN‐γ–/– mice, and IFN‐γ protein and the IFN‐γ‐inducible CXC chemokine, IP‐10, were present in 24‐hr ear tissue extracts, suggesting Th1 effects. Finally, ear swelling, total histology and eosinophils were decreased in mice deficient in CXCR3, the chemokine receptor for IP‐10. These results suggest that both a Th2‐like (IL‐5, IL‐4 and STAT‐6) and a Th1‐like (IFN‐γ, IP‐10, CXCR3) pathway contribute to eosinophil recruitment in early delayed‐type hypersensitivity.