IFNgamma differentially controls the development of idiopathic pneumonia syndrome and GVHD of the gastrointestinal tract.

Although proinflammatory cytokines are key mediators of tissue damage during graft-versus-host disease (GVHD), IFNgamma has previously been attributed with both protective and pathogenic effects. We have resolved this paradox by using wild-type (wt), IFNgamma(-/-), and IFNgammaR(-/-) mice as donors or recipients in well-described models of allogeneic stem cell transplantation (SCT). We show that donor-derived IFNgamma augments acute GVHD via direct effects on (1) the donor T cell to promote T helper 1 (Th1) differentiation and (2) the gastrointestinal (GI) tract to augment inflammatory cytokine generation. However, these detrimental effects are overwhelmed by a protective role of IFNgamma in preventing the development of idiopathic pneumonia syndrome (IPS). This is the result of direct effects on pulmonary parenchyma to prevent donor cell migration and expansion within the lung. Thus, IFNgamma is the key cytokine differentially controlling the development of IPS and gastrointestinal GVHD after allogeneic SCT.

CXCL16 regulates cell-mediated immunity to Salmonella enterica serovar Enteritidis via promotion of gamma interferon production.

CXCL16 is a recently discovered multifaceted chemokine that has been shown not only to recruit activated T lymphocytes but also to play a direct role in the binding and phagocytosis of bacteria by professional antigen-presenting cells. In this study, we investigated the role of CXCL16 in vivo in the regulation of the immune response using a murine model of Salmonella enterica serovar Enteritidis infection. The expression of CXCL16 was strongly upregulated in the spleens and livers of animals developing an immune response to a primary acute infection but not in the Peyer's patches. Animals developing a secondary response after reexposure to the bacteria displayed a similar pattern of expression. During the primary response, prior treatment with neutralizing antibodies to CXCL16 induced a significant increase in bacterial burden in the spleen and liver. The production of gamma interferon (IFN-gamma) by the lymphocytes in the spleen was decreased by anti-CXCL16 treatment. In comparison, during the secondary response, anti-CXCL16 treatment also significantly increased bacterial burden in both the spleen and liver but had no effect on IFN-gamma production. No role was found for CXCL16 in the production of antibody against SefA, a major surface antigen of S. enteritidis. Together, these results demonstrate a role for CXCL16 in the control of bacterial colonization of target organs and, more specifically, in the regulation of the cell-mediated arm of the primary response to S. enteritidis.

Control of Salmonella dissemination in vivo by macrophage inflammatory protein (MIP)-3alpha/CCL20.

While chemokines are clearly important in the generation of protective immunity, the role of individual chemokines in the control of bacterial infection is still poorly understood. In this study, we investigated the role of macrophage inflammatory protein (MIP)-3alpha/CCL20, a chemokine that attracts activated T and B lymphocytes and immature dendritic cells, in host responses to bacterial infection. CCL20 production was induced in subcutaneous tissue in the BALB/c mouse in response to Salmonella enteritidis, Staphylococcus aureus and zymosan, with S. enteritidis being the most potent. S. enteritidis induced CCL20 production in the spleen following either oral administration or injection into the peritoneal cavity. In contrast, no increase was observed in the Peyer's patches. In this model, following intraperitoneal injection, dose-dependent colonization of the spleen and Peyer's patches by S. enteritidis, expression of IFNgamma and IL-4, and production of antibodies against the S. enteritidis surface antigen SefA were observed. Prior treatment with neutralizing antibodies against CCL20 enhanced bacterial dissemination to the spleen and Peyer's patches and strongly biased the IFNgamma/IL-4 ratio towards a type 2 profile in the spleen, while the humoral response was unaffected. In contrast, treatment with neutralizing anti-MIP-1alpha/CCL3 antibodies enhanced the bacterial burden in the Peyer's patches but not in the spleen, had no significant effect on the cytokine ratio, but significantly inhibited anti-SefA production. Together, these results demonstrate an important role for CCL20 in the control of bacterial infection and more specifically in the regulation of cell-mediated immunity against intracellular bacteria such as S. enteritidis.

Inhibition of cytokine-induced fractalkine production by bacterial invasion of human-dermal fibroblasts.

Fractalkine (FKN/CX3CL1) is an atypical chemokine, for which a major biological function has not yet emerged. However, recent data suggest a role in immune responses in the skin. In this study, we analyzed fractalkine (FKN) secretion by human-dermal fibroblasts after exposure to pro-inflammatory cytokines or to invasive and noninvasive strains of Escherichia coli. Incubation of fibroblasts with TNF-alpha and IL-1beta induced a delayed expression of soluble FKN, compared with the rapid secretion of other chemokines including IL-8 (CXCL8), monocyte chemotactic protein-1 (CCL2), and RANTES (regulated upon activation, normal T cell expressed and secreted; CCL5). TNF-alpha and IFN-gamma gamma were more potent at inducing FKN secretion than was IL-1beta. Very little FKN was detected on the cell surface. FKN was not detected after incubation with the bacteria, regardless of the strain used. In contrast, both invasive and noninvasive E. coli triggered the release of IL-8 and monocyte chemotactic protein-1 in a dose-response manner, whereas RANTES was produced only in response to the invasive strain. Finally, incubation of fibroblasts with the invasive strain of E. coli inhibited TNF-alpha- and IFN-gamma-induced production of FKN. These results demonstrate for the first time that human-dermal fibroblasts express FKN, and that the characteristics of FKN secretion are distinct from those of other chemokines produced by these cells during immune responses in the dermis. In addition, our data indicate that bacterial invasion of dermal fibroblasts actively modulates FKN expression.

CCR3-blocking antibody inhibits allergen-induced eosinophil recruitment in human skin xenografts from allergic patients.

Eosinophil, basophil, and T helper 2 (TH2) cell recruitment into tissues is a characteristic feature of allergic diseases. These cells have in common the expression of the chemokine receptor CCR3, which may represent a specific pathway for their accumulation in vivo. Although animal models of allergic reactions are available, findings cannot always be extrapolated to man. To overcome these limitations, we have developed a humanized mouse model of allergic cutaneous reaction using severe combined immunodeficiency mice engrafted with skin and autologous peripheral blood mononuclear cells from allergic donors. Intradermal injection of the relevant allergen into human skin xenografts from allergic individuals induced a significant recruitment of human CD4(+) T cells, basophils, and TH2-type cytokine mRNA-expressing cells, as well as murine eosinophils. Human skin xenografts, atopic status, and autologous peripheral blood mononuclear cell reconstitution were all mandatory to induce the allergic reaction. Next, we addressed the role of CCR3 in the endogenous mechanisms involved in the inflammatory cell recruitment in this experimental model of allergic cutaneous reaction. In vivo administration of an anti-human CCR3-blocking antibody selectively reduced accumulation of eosinophils but not that of CD4(+) cells, basophils, or cells expressing mRNA for TH2-type cytokines. These findings establish a new in vivo model of humanized allergic reaction and suggest that eosinophil migration is mediated mainly through CCR3. Finally, these results suggest that this model might be useful to test human-specific antiallergic modulators.

Diesel exposure favors Th2 cell recruitment by mononuclear cells and alveolar macrophages from allergic patients by differentially regulating macrophage-derived chemokine and IFN-gamma-induced protein-10 production.

Diesel exhausts and their associated organic compounds may be involved in the recent increase in the prevalence of allergic disorders, through their ability to favor a type 2 immune response. Type 2 T cells have been shown to be preferentially recruited by the chemokines eotaxin (CCL11), macrophage-derived chemokine (MDC, CCL22), and thymus activation-regulated chemokine (CCL17) through their interaction with CCR3 and CCR4, respectively, whereas type 1 T cells are mainly recruited by IFN-gamma-induced protein-10 (CXCL10) through CXCR3 binding. The aim of the study was to evaluate the effect of diesel exposure on the expression of chemokines involved in type 1 and 2 T cell recruitment. PBMC and alveolar macrophages from house dust mite allergic patients were incubated with combinations of diesel extracts and Der p 1 allergen, and chemokine production was analyzed. Diesel exposure alone decreased the constitutive IP-10 production, while it further augmented allergen-induced MDC production, resulting in a significantly increased capacity to chemoattract human Th2, but not Th1 clones. Inhibition experiments with anti-type 1 or type 2 cytokine Abs as well as cytokine mRNA kinetic evaluation showed that the chemokine variations were not dependent upon IL-4, IL-13, or IFN-gamma expression. In contrast, inhibition of the B7:CD28 pathway using a CTLA-4-Ig fusion protein completely inhibited diesel-dependent increase of allergen-induced MDC production. This inhibition was mainly dependent upon the CD86 pathway and to a lesser extent upon the CD80 pathway. These results suggest that the exposure to diesel exhausts and allergen may likely amplify a deleterious type 2 immune response via a differential regulation of chemokine production through the CD28 pathway.