Altered Chemokine Profile Associated with Exacerbated Autoimmune Pathology under Conditions of Genetic Interferon-γ Deficiency

Experimental autoimmune uveoretinitis (EAU) is an organ-specific, CD4+ T-cell–mediated disease, that can be induced in genetically susceptible strains of mice after immunization with retinal proteins, such as interphotoreceptor retinoid– binding protein (IRBP) or S-antigen (arrestin), or by the adoptive transfer of T-cells specific for these antigens.1,2 EAU is characterized by granulomatous inflammation in the neural retina, vasculitis, destruction of photoreceptor cells, and blindness.3,4 The pathology seen in EAU strikingly resembles human uveitic diseases of putative autoimmune etiology, such as ocular sarcoidosis and Behcet’s disease3–5 and serves as a model for these diseases, as well as a model for organ-specific autoimmunity mediated by T-cells. Effector T-lymphocytes can be divided into several subsets including Th1, Th2, and Th17, based on their patterns of cytokine production.6–13 Th-1 type cells secrete interferon (IFN)- γ and IL-2, and are responsible for directed cell-mediated immune responses such as delayed-type hypersensitivity (DTH). Th2 cells secrete IL-4, Il-5, and IL-13 and are involved in humoral immunity and allergic responses. Th17 cells secrete IL-17, TNF-α, and IL-6, and have been implicated in inflammatory responses. Previous data from our laboratory showed that depletion of systemic IFN-γ by anti IFN-γ antibodies exacerbates disease in the mouse EAU model, and some strains normally resistant to EAU-induction develop disease after treatment with anti-IFN-γ antibodies.14 Furthermore, IFN-γ-deficient (GKO) mice are more susceptible to EAU and to EAE compared with their wild-type (WT) control littermates. 15,16 Of note, GKO mice develop a deviant effector response that differs from that of wild-type mice, in that it contains a prominent component of granulocytes in the inflammatory infiltrate, resembling the responses in Th2-mediated diseases.15–17 Entry of immune cells into and their retention and activation within tissues are crucial features of host immune response against pathogens and of autoimmune pathogenesis. The migration of immune cells to target organs depends on the gradient of chemokines in the inflammatory sites. Chemokines are a group of small (8 –10-kDa), secreted polypeptides and can be divided into families based on their structure—in particular, the motif of the first two of four cysteine residues in their amino acid structure. The largest family, CCL, has cysteine residues adjacent to each other, whereas the CXCL family has an intervening amino acid between the cysteine residues. Two smaller families XCL (containing only two cysteine residues) and CX3CL (with three intervening amino acids) complete the chemokine group.18,19 The migration of leukocytes induced by chemokines is based on the expression of cognate chemokine receptors on leukocytes. Each subset of immune cells expresses various levels of chemokine receptors. Th1 T cells predominantly express CXCR3 and CCR5. Therefore, the main cognate ligands for these receptors, CXCL9, CXCL10, CXCL11, and CCL5, are known as Th1-associated chemokines.20,21 Th2 selectively express CCR3, CCR4, and CCR8. The main cognate ligands for these receptors, CCR8, CCL11, CCL17, and CCL1, are known as Th2-associated chemokines.21,22 The Th2 chemokines also attract granulocytes. The recently described Th17 effectors are associated with CCL6, CXCL2 (the murine IL-8 equivalent) CCL7, CCL20, and CCL22.23,24 Chemokines are critical mediators in the pathogenesis of many diseases. For example, CCL3, CCL2, CCL5, CXCL9, and CXCL10 are upregulated in the eyes at the onset of EAU.25–27 Fife et al.28 reported that CXCL10 is a crucial chemokine in the recruitment and accumulation of inflammatory mononuclear cells during the pathogenesis of EAE. Our previous data showed that blockade of chemokine signaling by pertussis toxin during the effector stage of EAU abrogates disease development. 29 In the present study, we examined the expression of chemokines in uveitic IFN-γ-deficient and wild-type C57BL6 mice. We found that the Th1-associated chemokines, CXCL10, CXCL9, CCL5, and CXCL11 were highly expressed in wild-type mice and were associated with a mononuclear infiltration into the eyes. In contrast, the Th2-associated chemokines CCL11, CCL17, and CCL1 and the Th17-associated chemokines CCL22 and CXCL2 were upregulated in GKO mice and were associated with a predominantly granulocytic infiltrate. These cytokine profiles may explain the differential recruitment of leukocyte subpopulation into uveitic eyes in the absence versus presence of an IFN-γ response. Importantly, as indicated by depletion studies, granulocytes are a necessary cellular element for pathogenesis in both GKO and WT genotypes.