Danielle D. Kish

Alloreactive T Cell Responses and Acute Rejection of Single Class II MHC-Disparate Heart Allografts Are under Strict Regulation by CD4+CD25+ T Cells

Skin but not vascularized cardiac allografts from B6.H-2bm12 mice are acutely rejected by C57BL/6 recipients in response to the single class II MHC disparity. The underlying mechanisms preventing acute rejection of B6.H-2bm12 heart allografts by C57BL/6 recipients were investigated. B6.H-2bm12 heart allografts induced low levels of alloreactive effector T cell priming in C57BL/6 recipients, and this priming was accompanied by low-level cellular infiltration into the allograft that quickly resolved. Recipients with long-term-surviving heart allografts were unable to reject B6.H-2bm12 skin allografts, suggesting potential down-regulatory mechanisms induced by the cardiac allografts. Depletion of CD25+ cells from C57BL/6 recipients resulted in 15-fold increases in alloreactive T cell priming and in acute rejection of B6.H-2bm12 heart grafts. Similarly, reconstitution of B6.Rag−/− recipients with wild-type C57BL/6 splenocytes resulted in acute rejection of B6.H-2bm12 heart grafts only if CD25+ cells were depleted. These results indicate that acute rejection of single class II MHC-disparate B6.H-2bm12 heart allografts by C57BL/6 recipients is inhibited by the emergence of CD25+ regulatory cells that restrict the clonal expansion of alloreactive T cells.

The intensity of neutrophil infiltration controls the number of antigen-primed CD8 T cells recruited into cutaneous antigen challenge sites.

Recruitment of antigen‐specific T cells into the skin is a critical initiating event during immune responses to many parasites and tumors as well as T cell‐mediated, cutaneous, allergic responses and autoimmune diseases. Mechanisms directing T cell trafficking into skin remain largely undefined. Here, we show that cutaneous contact with reactive antigen induces KC/CXC chemokine ligand 1 production and neutrophil infiltration in an antigen, dose‐dependent manner. The intensity of neutrophil infiltration into cutaneous antigen challenge sites, in turn, controls the number of antigen‐primed T cells recruited into the site and the magnitude of the immune response elicited. The absence of responses in immune animals challenged with suboptimal doses of antigen is overcome by manipulating neutrophil infiltration that then directs antigen‐primed T cell infiltration into the challenge site. This inflammation also directs T cells primed to one antigen (dinitrofluorobenzene) into the site when challenged with a completely different antigen (oxazolone). These results identify the intensity of neutrophil infiltration into cutaneous, antigen‐deposition sites as a critical parameter for the level of antigen‐primed T cell recruitment to mediate the adaptive immune response. This interplay between the innate and adaptive responses suggests a strategy to modulate, in a positive or negative manner, antigen‐primed T cell infiltration into cutaneous inflammation sites.

CD8 T Cells Producing IL-17 and IFN-γ Initiate the Innate Immune Response Required for Responses to Antigen Skin Challenge

Effector CD8 T cell recruitment into the skin in response to Ag challenge requires prior CXCL1/KC-directed neutrophil infiltration. Mechanisms inducing CXCL1 production and the dynamics of neutrophil-CD8 T cell interactions during elicitation of Ag-specific responses in the skin were investigated. CXCL1 and CXCL2/MIP-2 were produced within 3–6 h of Ag challenge at 10-fold higher levels in skin challenge sites of Ag-sensitized vs nonsensitized mice. In the challenge sites of sensitized mice this production decreased at 6–9 h postchallenge to near the levels observed in skin challenge sites of nonsensitized mice but rose to a second peak 12 h after challenge. The elevated early neutrophil chemoattractant production at 3–6 h after skin challenge of sensitized animals required both IFN-γ and IL-17, produced by distinct populations of Ag-primed CD8 T cells in response to Ag challenge. Although induced by the Ag-primed CD8 T cells, the early CXCL1 and CXCL2 production was accompanied by neutrophil but not CD8 T cell infiltration into the skin Ag challenge site. Infiltration of the CD8 T cells into the challenge site was not observed until 18–24 h after challenge. These results demonstrate an intricate series of early interactions between Ag-specific and innate immune components that regulate the sequential infiltration of neutrophils and then effector T cells into the skin to mediate an immune response.

CD8+ T cells produce IL‐2, which is required for CD4+CD25+ T cell regulation of effector CD8+ T cell development for contact hypersensitivity responses

Interleukin (IL)‐2 functions to promote, as well as down‐regulate, expansion of antigen‐reactive CD4+ and CD8+ T cells, but the role of IL‐2 in hapten‐specific CD8+ T cell priming for contact hypersensitivity (CHS) responses remains untested. Using enzyme‐linked immunospot to enumerate numbers of hapten‐specific CD4+ and CD8+ T cells producing IL‐2 in hapten‐sensitized mice, the number of IL‐2‐producing CD8+ T cells was tenfold that of CD4+ T cells. Hapten‐primed D4+ T cells produced low amounts of IL‐2 during culture with hapten‐presenting Langerhans cells, whereas production by hapten‐primed CD8+ T cells was fivefold greater. CD8+ T cells did not express CD25 during hapten priming, but treatment with anti‐IL‐2 or anti‐CD25 monoclonal antibodies during hapten sensitization increased hapten‐specific effector CD8+ T cells as well as the magnitude and duration of the CHS response. These results indicate that CD8+ T cells are the primary source of IL‐2 and that this IL‐2 is required for the function of a population of CD4+CD25+ T cells to restrict the development of the hapten‐reactive effector CD8+ T cells that mediate CHS responses.

CXC Chemokine Ligand (CXCL) 9 and CXCL10 Are Antagonistic Costimulation Molecules during the Priming of Alloreactive T Cell Effectors

Donor Ag-reactive CD4 and CD8 T cell production of IFN-γ is a principal effector mechanism promoting tissue injury during allograft rejection. The CXCR3-binding chemokines CXCL9 and CXCL10 recruit donor-reactive T cells to the allograft, but their role during the priming of donor-reactive T cells to effector function is unknown. Using a murine model of MHC-mismatched cardiac transplantation, we investigated the influence of CXCL9 and CXCL10 during donor-reactive T cell priming. In allograft recipient spleens, CXCL9 and CXCL10 were expressed as early as 24 h posttransplant and increased with similar kinetics, concurrently with CXCR3 expression on T cells. CXCL9, but not CXCL10, expression required NK cell production of IFN-γ. The absence of CXCL9 in donor allografts, recipients, or both significantly decreased the frequency of donor-reactive CD8 T cells producing IFN-γ and increased the frequency of donor-reactive CD8 T cells producing IL-17A. In contrast, the absence of CXCL10 increased the frequency of IFN-γ–producing CD8 T cells in a CXCL9-dependent manner. These data provide novel evidence that donor-reactive CD8 T cells use the CXCR3 chemokine axis as a costimulation pathway during priming to allografts where CXCL9 promotes the development of IFN-γ–producing CD8 T cells, and CXCL10 antagonizes this skewing.

Absence of allograft ICAM-1 attenuates alloantigen-specific T cell priming, but not primed T cell trafficking into the graft, to mediate acute rejection

The expression and function of ICAM-1 are critical components in the initiation and elicitation of many T cell-mediated responses. Whether ICAM-1 expression is required on the T cells or on the APC during T cell priming remains unclear. To address this issue in alloantigen-specific T cell activation, the priming and function of T cells in response to heart allografts from MHC-mismatched wild-type vs ICAM-1−/− donors were tested. Wild-type C57BL/6 (H-2b) heart allografts were rejected by A/J (H-2a) recipients on days 7–9, whereas B6.ICAM-1−/− allografts survived until days 18–23 post-transplant. On day 7 post-transplant, infiltrating macrophages and CD4+ and CD8+ T cells in the ICAM-1−/− allografts were 20–30% those observed in the wild-type allografts. ELISPOT analyses indicated that the number of alloantigen-specific T cells producing IFN-γ from recipients of ICAM-1-deficient grafts was 60% lower than that from recipients of wild-type allografts. On day 16 post-transplant, these numbers did not markedly increase in ICAM-1-deficient allograft recipients. Consistent with the reduced priming of alloreactive T cells, isolated dendritic cells from ICAM-1−/− mice stimulated allogeneic T cell proliferation poorly compared with wild-type dendritic cells. When A/J mice were primed with wild-type dendritic cells and then received wild-type or ICAM-1-deficient heart allografts 3 days later, the primed recipients rejected the wild-type and ICAM-1−/− allografts on days 5–6 post-transplant. These results indicate that optimal priming of alloreactive T cells requires allograft expression of ICAM-1, but, once primed, recipient T cell infiltration into the allograft is independent of graft ICAM-1 expression.

Neutrophil Expression of Fas Ligand and Perforin Directs Effector CD8 T Cell Infiltration into Antigen-Challenged Skin

Contact hypersensitivity (CHS) is a T cell response to hapten skin challenge of sensitized individuals proposed to be mediated by hapten-primed CD8 cytolytic T cells. Effector CD8 T cell recruitment into hapten challenge sites to elicit CHS requires prior CXCL1- and CXCL2-mediated neutrophil infiltration into the site. We investigated whether neutrophil activities directing hapten-primed CD8 T cell skin infiltration in response to 2,4-dinitro-1-fluorobenzene (DNFB) required Fas ligand (FasL) and perforin expression. Although DNFB sensitization of gld/perforin−/− mice induced hapten-specific CD8 T cells producing IFN-γ and IL-17, these T cells did not infiltrate the DNFB challenge site to elicit CHS but did infiltrate the challenge site and elicit CHS when transferred to hapten-challenged naive wild-type recipients. Hapten-primed wild-type CD8 T cells, however, did not elicit CHS when transferred to naive gld/perforin−/− recipients. Wild-type bone marrow neutrophils expressed FasL and perforin, and when transferred to sensitized gld/perforin−/− mice, they restored hapten-primed CD8 T cell infiltration into the challenge site and CHS. The FasL/perforin-mediated activity of wild-type neutrophils induced the expression of T cell chemoattractants, CCL1, CCL2, and CCL5, within the hapten-challenged skin. These results indicate FasL/perforin-independent functions of hapten-primed CD8 T cells in CHS and identify new functions for neutrophils in regulating effector CD8 T cell recruitment and immune responses in the skin.

Hapten Application to the Skin Induces an Inflammatory Program Directing Hapten-Primed Effector CD8 T Cell Interaction with Hapten-Presenting Endothelial Cells

Contact hypersensitivity is a CD8 T cell-mediated response to hapten sensitization and challenge of the skin. Effector CD8 T cell recruitment into the skin parenchyma to elicit the response to hapten challenge requires prior CXCL1/KC-directed neutrophil infiltration within 3–6 h after challenge and is dependent on IFN-γ and IL-17 produced by the hapten-primed CD8 T cells. Mechanisms directing hapten-primed CD8 T cell localization and activation in the Ag challenge site to induce this early CXCL1 production in response to 2,4-dinitrofluorobenzene were investigated. Both TNF-α and IL-17, but not IFN-γ, mRNA was detectable within 1 h of hapten challenge of sensitized mice and increased thereafter. Expression of ICAM-1 was observed by 1 h after challenge of sensitized and nonsensitized mice and was dependent on TNF-α. The induction of IL-17, IFN-γ, and CXCL1 in the challenge site was not observed when ICAM-1 was absent or neutralized by specific Ab. During the elicitation of the contact hypersensitivity response, endothelial cells expressed ICAM-1 and produced CXCL1 suggesting this as the site of CD8 T cell localization and activation. Endothelial cells isolated from challenged skin of naive and sensitized mice had acquired the hapten and the ability to activate hapten-primed CD8 T cell cytokine production. These results indicate that hapten application to the skin of sensitized animals initiates an inflammatory response promoting hapten-primed CD8 T cell localization to the challenge site through TNF-α–induced ICAM-1 expression and CD8 T cell activation to produce IFN-γ and IL-17 through endothelial cell presentation of hapten.

Regulatory function of CD4+CD25+ T cells from Class II MHC-deficient mice in contact hypersensitivity responses

Contact hypersensitivity (CHS) is a CD8+ T cell‐mediated, inflammatory response to hapten sensitization and challenge of the skin. During sensitization, the magnitude and duration of hapten‐specific CD8+ T cell expansion in the skin‐draining lymph nodes (LN) are restricted by CD4+CD25+ T regulatory cells (Treg). The regulation of hapten‐specific CD8+ T cell priming in Class II MHC‐deficient (MHC–/–) mice was investigated. Although hapten‐specific CD8+ T cell priming and CHS responses were elevated in Class II MHC–/– versus wild‐type mice, presensitization depletion of CD4+ or CD25+ cells in Class II MHC–/– mice further increased CD8+ T cell priming and the elicited CHS response. Flow cytometry analyses of LN cells from Class II MHC–/– mice revealed a population of CD4+ T cells with a majority expressing CD25. Forkhead box p3 mRNA was expressed in LN cells from Class II MHC–/– and was reduced to background levels by depletion of CD4+ or CD25+ cells. Isolated CD4+CD25+ T cells from wild‐type and Class II MHC–/– mice limited in vitro proliferation of alloantigen‐ and hapten‐specific T cells to antigen‐presenting stimulator cells. These results identify functional CD4+CD25+ Treg in Class II MHC–/– mice, which restrict hapten‐specific CD8+ T cell priming and the magnitude of CHS responses.

Skin Allograft Rejection Is Suppressed in Mice Lacking the Antiviral Enzyme, 2′,5′-Oligoadenylate-Dependent RNase L

The 2-5A/RNase L system is a regulated RNA decay pathway that mediates some of the antiviral and tumor suppressor activities of the interferons. Previously, we demonstrated that RNase L-null mice have increased susceptibility to viral infections and are partially deficient in induced and spontaneous apoptosis. To determine if RNase L functions in cellular, as well as innate, immunity, skin allograft rejection and contact hypersensitivity (CHS) experiments were performed in RNase L+/+ and RNase L-/- mice. Although no consistent alterations in CHS were found, we did observe a delay of 5 days in the acute rejection of class II major histocompatibility complex (MHC) disparate skin allografts in mice lacking RNase L. Accordingly, histologic examinations of the allografts harvested from RNase L-/- mice revealed a dramatic reduction in inflammatory infiltrates, suggesting a delay in T-cell priming or a deficiency in immune cell trafficking. Results consistent with a proinflammatory role for RNase L extend the known functions of the 2-5A/RNase L system beyond innate immunity into some, but not all, types of cellular immunity.