Role of IL-16 in delayed-type hypersensitivity reaction

Abstract

Interleukin (IL)-16 is a chemoattractant cytokine for CD4+ leukocytes. Because delayed-type hypersensitivity (DTH) reaction is mediated by T helper 1 (Th1) cells and CD4+ T cells can be chemoattracted by IL-16, we have investigated the involvement of IL-16 in the DTH reaction. Immunohistochemical analysis revealed the IL-16 expression in infiltrating cells and epithelial cells in the DTH footpads. The IL-16 expression was also detected intracellularly in the infiltrating cells. In addition, markedly increased production of IL-16 was detected in the DTH footpad extracts, but not in the control footpad extracts, by an enzyme-linked immunosorbent assay and also by Western blot analysis. The DTH footpad extracts exhibited a strong chemoattractant activity toward splenic T cells, which was significantly inhibited by the inclusion of neutralizing monoclonal antibody (mAb) against IL-16 in the migration assay. Furthermore, treatment of sensitized mice in vivo with the anti-IL-16 neutralizing mAb significantly suppressed the footpad swelling induced by an antigen challenge, together with decreased infiltration of leukocytes including not only CD4+ T cells but also CD8+ T cells and macrophages into the DTH footpads. Decreased production of macrophage inflammatory protein 1 was also observed in the DTH footpad extracts by the mAb treatment. These results suggest that IL-16 plays an important role in the recruitment of leukocytes—presumably including antigen-specific Th1 cells, which secrete cytokines and chemokines mediating the following hypersensitivity reaction after activation by the interaction with Langerhans cells carrying the antigen—for the elicitation of DTH response.