Christina M. Parker

Essential role for CD103 in the T cell–mediated regulation of experimental colitis

The integrin CD103 is highly expressed at mucosal sites, but its role in mucosal immune regulation remains poorly understood. We have analyzed the functional role of CD103 in intestinal immune regulation using the T cell transfer model of colitis. Our results show no mandatory role for CD103 expression on T cells for either the development or CD4+CD25+ regulatory T (T reg) cell–mediated control of colitis. However, wild-type CD4+CD25+ T cells were unable to prevent colitis in immune-deficient recipients lacking CD103, demonstrating a nonredundant functional role for CD103 on host cells in T reg cell–mediated intestinal immune regulation. Non–T cell expression of CD103 is restricted primarily to CD11chighMHC class IIhigh dendritic cells (DCs). This DC population is present at a high frequency in the gut-associated lymphoid tissue and appears to mediate a distinct functional role. Thus, CD103+ DCs, but not their CD103− counterparts, promoted expression of the gut-homing receptor CCR9 on T cells. Conversely, CD103− DCs promoted the differentiation of IFN-γ–producing T cells. Collectively, these data suggest that CD103+ and CD103− DCs represent functionally distinct subsets and that CD103 expression on DCs influences the balance between effector and regulatory T cell activity in the intestine.

Structure of the integrin VLA-4 and its cell-cell and cell-matrix adhesion functions.

Article synthese sur la variabilite de la structure moleculaire et sur la diversite fonctionnelle de la proteine VLA-4 appartenant a la famille des integrines

Constitutive expression of stromal derived factor-1 by mucosal epithelia and its role in HIV transmission and propagation

HIV particles that use the chemokine receptor CXCR4 as a coreceptor for entry into cells (X4-HIV) inefficiently transmit infection across mucosal surfaces [1], despite their presence in seminal fluid and mucosal secretions from infected individuals [2] [3] [4]. In addition, although intestinal lymphocytes are susceptible to infection with either X4-HIV particles or particles that use the chemokine receptor CCR5 for viral entry (R5-HIV) during ex vivo culture [5], only systemic inoculation of R5-chimeric simian-HIV (S-HIV) results in a rapid loss of CD4(+) intestinal lymphocytes in macaques [6]. The mechanisms underlying the inefficient capacity of X4-HIV to transmit infection across mucosal surfaces and to infect intestinal lymphocytes in vivo have remained elusive. The CCR5 ligands RANTES, MIP-1alpha and MIP-1beta suppress infection by R5-HIV-1 particles via induction of CCR5 internalization, and individuals whose peripheral blood lymphocytes produce high levels of these chemokines are relatively resistant to infection [7] [8] [9]. Here, we show that the CXCR4 ligand stromal derived factor-1 (SDF-1) is constitutively expressed by mucosal epithelial cells at sites of HIV transmission and propagation. Furthermore, CXCR4 is selectively downmodulated on intestinal lymphocytes within the setting of prominent SDF-1 expression. We postulate that mucosally derived SDF-1 continuously downmodulates CXCR4 on resident HIV target cells, thereby reducing the transmission and propagation of X4-HIV at mucosal sites. Moreover, such a mechanism could contribute to the delayed emergence of X4 isolates, which predominantly occurs during the later stages of the HIV infection.

Human intestinal lamina propria and intraepithelial lymphocytes express receptors specific for chemokines induced by inflammation

To determine which chemokine receptors might be involved in T lymphocyte localization to the intestinal mucosa, we examined receptor expression on human intestinal lamina propria lymphocytes (LPL), intraepithelial lymphocytes (IEL) and CD45RO+β7hi gut homing peripheral blood lymphocytes (PBL). Virtually all LPL and IEL expressed CXCR3 and CCR5, receptors that have been associated with Th1(Tc1) / Th0 lymphocytes, while CCR3 and CCR4, receptors associated with Th2 (Tc2) lymphocytes, CCR7, CXCR1 and CXCR2 were not expressed. CXCR3 and CCR5 receptors were functional, as LPL and IEL migrated to their respective ligands I‐TAC and RANTES. In addition, most α Eβ 7– LPL and IEL expressed high levels of CCR2. While the majority of CD45RO+β 7hi PBL also expressed CXCR3 and CCR5, a proportion of these cells were CXCR3– and/or CCR5– and some expressed CCR4 and/or CCR7, indicating that lymphocytes recruited to the intestinal mucosa represent a subset of these cells. In summary, our results show that LPL and IEL within the normal intestine express a specific and similar array of chemokine receptors whose ligands are constitutively expressed in the intestinal mucosa and whose expression is up‐regulated during intestinal inflammation. These results support the view that CXCR3, CCR5 and CCR2 may play an important role in lymphocyte localization within the intestinal mucosa.

T-lymphocyte-epithelial-cell interactions: integrin alpha(E)(CD103)beta(7), LEEP-CAM and chemokines

The epithelia are the avascular layers of cells that cover the environment-exposed surfaces of the body. It appears that T cells localize to selected sites in or adjacent to epithelia via the selective expression of adhesion molecules and chemokine receptors on T cells. These bind to counter-receptors and to chemokines expressed by epithelial cells. Recently, there has been an advance in our understanding of the interaction of the alpha(Ebeta7) integrin with its epithelial cell ligand, E-cadherin. In addition, a new adhesion molecule has been identified on non-intestinal epithelial cells, termed lymphocyte-endothelial-epithelial-cell adhesion molecule (LEEP-CAM). Finally, there have been advances in our understanding of the role of skin- or gut-epithelia-derived chemokines in regulating activated T cell homing to these sites.

Efomycine M, a new specific inhibitor of selectin, impairs leukocyte adhesion and alleviates cutaneous inflammation

Specific interference with molecular mechanisms guiding tissue localization of leukocytes may be of great utility for selective immunosuppressive therapies. We have discovered and characterized efomycines, a new family of selective small-molecule inhibitors of selectin functions. Members of this family significantly inhibited leukocyte adhesion in vitro. Efomycine M, which was nontoxic and showed the most selective inhibitory effects on selectin-mediated leukocyte-endothelial adhesion in vitro, significantly diminished rolling in mouse ear venules in vivo as seen by intravital microscopy. In addition, efomycine M alleviated cutaneous inflammation in two complementary mouse models of psoriasis, one of the most common chronic inflammatory skin disorders. Molecular modeling demonstrated a spatial conformation of efomycines mimicking naturally occurring selectin ligands. Efomycine M might be efficacious in the treatment of human inflammatory disorders through a similar mechanism.

CD103 Expression Is Required for Destruction of Pancreatic Islet Allografts by CD8+ T Cells

The mechanisms by which CD8 effector populations interact with epithelial layers is a poorly defined aspect of adaptive immunity. Recognition that CD8 effectors have the capacity to express CD103, an integrin directed to the epithelial cell-specific ligand E-cadherin, potentially provides insight into such interactions. To assess the role of CD103 in promoting CD8-mediated destruction of epithelial layers, we herein examined the capacity of mice with targeted disruption of CD103 to reject pancreatic islet allografts. Wild-type hosts uniformly rejected islet allografts, concomitant with the appearance of CD8+CD103+ effectors at the graft site. In contrast, the majority of islet allografts transplanted into CD103−/− hosts survived indefinitely. Transfer of wild-type CD8 cells into CD103−/− hosts elicited prompt rejection of long-surviving islet allografts, whereas CD103−/− CD8 cells were completely ineffectual, demonstrating that the defect resides at the level of the CD8 cell. CD8 cells in CD103−/− hosts exhibited normal effector responses to donor alloantigens in vitro and trafficked normally to the graft site, but strikingly failed to infiltrate the islet allograft itself. These data establish a causal relationship between CD8+CD103+ effectors and destruction of graft epithelial elements and suggest that CD103 critically functions to promote intragraft migration of CD8 effectors into epithelial compartments.

In Vivo Roles of Integrins During Leukocyte Development and Traffic: Insights from the Analysis of Mice Chimeric for α5, αv, and α4 Integrins

Mice chimeric for integrins α5, αV, or α4 were used to dissect the in vivo roles of these adhesion receptors during leukocyte development and traffic. No major defects were observed in the development of lymphocytes, monocytes, or granulocytes or in the traffic of lymphocytes to different lymphoid organs in the absence of α5 or αV integrins. However, in agreement with previous reports, the absence of α4 integrins produced major defects in development of lymphoid and myeloid lineages and a specific defect in homing of lymphocytes to Peyer’s patches. In contrast, the α4 integrin subunit is not essential for localization of T lymphocytes into intraepithelial and lamina propria compartments in the gut, whereas one of the partners of α4, the β7 chain, has been shown to be essential. However, α4-deficient T lymphocytes cannot migrate properly during the inflammatory response induced by thioglycolate injection into the peritoneum. Finally, in vitro proliferation and activation of lymphocytes deficient for α5, αV, or α4 integrins upon stimulation with different stimuli were similar to those seen in controls. These results show that integrins play distinct roles during in vivo leukocyte development and traffic.

Integrin αE(CD103)β7 Mediates Adhesion to Intestinal Microvascular Endothelial Cell Lines Via an E-Cadherin-Independent Interaction

Integrins are important for T cell interactions with endothelial cells. Because the integrin αEβ7 is expressed on some circulating gut-homing T cells and as T cell numbers are reduced in the intestinal lamina propria of αE-deficient mice, we evaluated whether αEβ7 mediates binding to intestinal endothelial cells. We found that anti-αEβ7 mAbs partially blocked the binding of cultured intraepithelial T cells to human intestinal microvascular endothelial cells (HIMEC). Furthermore, αEβ7-transfected K562 cells bound more efficiently than vector-transfected K562 cells to HIMEC. Finally, HIMEC bound directly to an αEβ7-Fc fusion protein. These interactions were partially blocked by anti-αEβ7 mAbs, and endothelial cell binding to the αEβ7-Fc was dependent upon the metal ion-dependent adhesion site within the αE A domain. Of note, the HIMEC lacked expression of E-cadherin, the only known αEβ7 counterreceptor as assessed by functional studies, flow cytometry, and RT-PCR. Thus, HIMEC/αEβ7 binding was independent of E-cadherin. In addition, this interaction appeared to be tissue selective, as HIMEC bound to the αEβ7-Fc, whereas microvascular endothelial cells from the skin did not. Finally, there was evidence for an αEβ7 ligand on intestinal endothelial cells in vivo, as αEβ7 expression enhanced lymphocyte binding around vessels in the lamina propria in tissue sections. Thus, we have defined a novel interaction for αEβ7 at a nonepithelial location. These studies suggest a role for αEβ7 in interactions with the intestinal endothelium that may have implications for intestinal T cell homing or functional responses.

Cutaneous Inflammatory Disorder in Integrin αE (CD103)-Deficient Mice

The integrin αEβ7 is thought to play an important role in the localization of mucosal, but not of cutaneous T lymphocytes. Thus, it was surprising that 89% of adult αE−/− mice on the 129/Sv × BALB/c background developed inflammatory skin lesions without an apparent infectious etiology. Skin inflammation correlated with αE deficiency in mice with a mixed 129/Sv × BALB/c background, but not in mice further backcrossed to BALB/c and housed in a second animal facility. These studies suggested that αE deficiency, in combination with other genetic and/or environmental factors, is involved in lesion development. The lesions were infiltrated by CD4+ T cells and neutrophils, and associated with increased expression of inflammatory cytokines. Furthermore, skin inflammation resulted from transfer of unfractionated αE−/− splenocytes into scid/scid mice, but not from transfer of wild-type splenocytes, suggesting that the lesions resulted from immune dysregulation. We also studied the role of αEβ7 in a murine model of hyperproliferative inflammatory skin disorders that is induced by transfer of minor histocompatibility-mismatched CD4+/CD45RBhigh T cells into scid/scid mice under specific environmental conditions. Under housing conditions that were permissive for lesion development, transfer of αE-deficient CD4+/CD45RBhigh T cells significantly exacerbated the cutaneous lesions as compared with lesions observed in mice reconstituted with wild-type donor cells. These experiments suggested that αE-expressing cells play an important role during the course of cutaneous inflammation. In addition, they suggest that αEβ7 deficiency, in combination with other genetic or environmental factors, is a risk factor for inflammatory skin disease.