Expression of selectin ligands on murine effector and IL-10-producing CD4+ T cells from non-infected and infected tissues

Endothelial selectins are crucial for the recruitment of leukocytes into sites of inflammation. On T cells, ligands for selectins become induced upon differentiation into the effector/memory stage. Initial in vitro studies suggested a correlation between the Th1 phenotype and ligand expression, but whether this also holds true in vivo remained uncertain. We here analyzed selectin ligands on CD4+ T cells producing IFN-gamma, IL-4 or IL-10, prototypic cytokines of the Th1, Th2 and Tr1 subset, respectively. We analyzed mice infected with influenza virus, the bacterium Listeria, and the parasites Toxoplasma (all Th1 models) or Nippostrongylus (Th2 model). A link between the Th1 phenotype and ligand expression was not found in vivo. Surprisingly, the potentially regulatory IL-10-producing T cells displayed the highest frequency of ligand-positive cells in general. Within the inflamed tissues, the frequencies of P-selectin-binding cells increased in the dominant subset, either Th1 or Th2. Up-regulation was also found for E-selectin ligands during influenza, but not Nippostrongylus infection. In conclusion, conditions driving T cell polarization into either Th1 or Th2 in vivo do not affect the expression of selectin ligands, but acquisition of P-selectin binding and hence migration into inflamed tissues is boosted by an inflammatory milieu.     

Lack of microbiota reduces innate responses and enhances adaptive immunity against Listeria monocytogenes infection

The intestinal microbiota influences not only metabolic processes, but also the mucosal and systemic immune systems. Here, we compare innate and adaptive immune responses against the intracellular pathogen Listeria monocytogenes in germfree (GF) and conventional mice. We show that animals without endogenous microbiota are highly susceptible to primary infection with impaired activation and accumulation of phagocytes to the site of infection. Unexpectedly, secondary infection with otherwise lethal dose resulted in survival of all GF animals which cleared bacteria more rapidly and developed a stronger antilisterial CD8⁺ memory T‐cell response compared to conventional mice. In summary, lack of the intestinal microbiota impairs early innate immunity, but enhances activation and expansion of memory T cells.     

CD2-mediated autocrine growth of herpes virus saimiri-transformed human T lymphocytes

Herpes virus saimiri (HVS) immortalizes T lymphocytes from a variety of primates and causes acute T cell lymphomas and leukemias in nonnatural primate hosts. Here we have analyzed the requirements for growth of three HVS-transformed human T cell lines. The cells expressed the phenotype of activated T cells: two were CD4+, and one was CD8+. All three cells responded to all allogeneic human cell lines tested with enhanced proliferation, production of interleukin 2 (IL-2), and increased expression of the IL-2 receptor. Binding of CD2 to its ligand CD58 was the critical event mediating stimulation because: (a) monoclonal antibodies (mAbs) to CD2 and to CD58, but not to a variety of other surface structures, blocked induced and spontaneous proliferation and IL-2 production; (b) only anti-CD2 mAbs were stimulatory if crosslinked; (c) a nonstimulatory cell was rendered stimulatory by CD58 transfection; and (d) the cells responded specifically to CD58 on sheep red blood cells. Growth of the cells required activation because cyclosporin A and FK506 blocked stimulator cell-induced IL-2 production and proliferation as well as the spontaneous growth of the lines. Antibodies to the IL-2 receptor reduced proliferation of the cells and blocked IL-2 utilization. Taken together, these results show that HVS-transformed T cells proliferate in response to CD2-mediated contact with stimulator cells or with each other in an IL-2-dependent fashion. They suggest that HVS transforms human T cells to an activation-dependent autocrine growth.     

Regional IFNgamma expression is insufficient for efficacious control of food-borne bacterial pathogens at the gut epithelial barrier

IFNgamma is critical for host defence against various food-borne pathogens including Salmonella enterica and Listeria monocytogenes, the causative agents of salmonellosis and listeriosis, respectively. We investigated the impact of regional IFNgamma expression at the intestinal epithelial barrier on host invasion by salmonellae and listeriae following oral challenge. Transgenic mice (IFNgamma-gut), generated on an IFNgamma knock-out (KO) background, selectively expressed IFNgamma in the gut driven by the modified liver fatty acid-binding protein (Fabpl(4x at -132)) promoter. Infections with attenuated S. enterica Typhimurium or with L. monocytogenes did not differ significantly in IFNgamma-KO, IFNgamma-gut and wild-type mice. Further, Listeria-specific CD4+ and CD8+ T cells were not altered in IFNgamma-gut mice. Thus, this model indicates that local IFNgamma expression by non-immunological cells in the distal part of the small intestine, caecum and colon is insufficient for prevention of gut penetration by S. enterica Typhimurium and L. monocytogenes.     

Chemokines play a critical role in the cross-regulation of Th1 and Th17 immune responses in murine crescentic glomerulonephritis

Th1 and Th17 subtype effector CD4(+) T cells are thought to play a critical role in the pathogenesis of human and experimental crescentic glomerulonephritis. The time course, mechanism, and functions of Th1 and Th17 cell recruitment, and their potential interaction in glomerulonephritis, however, remain to be elucidated. We performed interventional studies using IL-17- and IFN-γ-gene-deficient mice, as well as neutralizing antibodies that demonstrated the importance of the Th17-mediated immune response during the early phase of the disease. At a later stage, we found that Th1 cells were critical mediators of renal tissue injury. Early recruitment of IL-17-producing Th17 cells triggered expression of the chemokine CXCL9 in the kidney that drove the infiltration of Th1 cells bearing its receptor CXCR3. At a later stage, Th1 cell-derived IFN-γ was found to inhibit local chemokine CCL20 expression, acting through its receptor CCR6 on Th17 cells, thereby limiting the renal Th17 immune response. Thus, our findings provide mechanistic evidence for a cytokine-chemokine-driven feedback loop that orchestrates the observed differential Th1 and Th17 cell infiltration into the inflamed kidney. This contributes to the observed time-dependent function of these two major pathogenic effector CD4(+) T cell subsets in crescentic glomerulonephritis.     

CXCL5-secreting pulmonary epithelial cells drive destructive neutrophilic inflammation in tuberculosis

Successful host defense against numerous pulmonary infections depends on bacterial clearance by polymorphonuclear leukocytes (PMNs); however, excessive PMN accumulation can result in life-threatening lung injury. Local expression of CXC chemokines is critical for PMN recruitment. The impact of chemokine-dependent PMN recruitment during pulmonary Mycobacterium tuberculosis infection is not fully understood. Here, we analyzed expression of genes encoding CXC chemokines in M. tuberculosis–infected murine lung tissue and found that M. tuberculosis infection promotes upregulation of Cxcr2 and its ligand Cxcl5. To determine the contribution of CXCL5 in pulmonary PMN recruitment, we generated Cxcl5^–/– mice and analyzed their immune response against M. tuberculosis. Both Cxcr2^–/– mice and Cxcl5^–/– mice, which are deficient for only one of numerous CXCR2 ligands, exhibited enhanced survival compared with that of WT mice following high-dose M. tuberculosis infection. The resistance of Cxcl5^–/– mice to M. tuberculosis infection was not due to heightened M. tuberculosis clearance but was the result of impaired PMN recruitment, which reduced pulmonary inflammation. Lung epithelial cells were the main source of CXCL5 upon M. tuberculosis infection, and secretion of CXCL5 was reduced by blocking TLR2 signaling. Together, our data indicate that TLR2-induced epithelial-derived CXCL5 is critical for PMN-driven destructive inflammation in pulmonary tuberculosis.     

Requirement of secondary lymphoid tissues for the induction of primary and secondary T cell responses against Listeria monocytogenes

Activation of naive T cells is tightly controlled and depends on cognate interactions with professional antigen-presenting cells. We analyzed dependency on secondary lymphoid tissues for the activation of naive and memory CD4(+) and CD8(+) T cells following primary and secondary Listeria monocytogenes infection, respectively. In splenectomized lymphotoxin-beta receptor-deficient mice, lacking all secondary lymphoid tissues, oral infection with L. monocytogenes failed to induce bacteria-specific CD4(+) and CD8(+) T cell responses. Treatment of splenectomized wild-type mice with FTY720, a drug that prevents egress of T cells from lymph nodes, also reduced T cell responses after oral L. monocytogenes infection and blocked T cell responses after intravenous infection. FTY720-treated wild-type and lymphotoxin-beta receptor-deficient mice show only slightly impaired recall responses. However, T cell responses were profoundly inhibited when mice were splenectomized subsequently to recovery from primary infection. T cell transfer experiments demonstrated that the impaired secondary T cell response was not simply due to removal of a large fraction of memory T cells by splenectomy. Overall, these results indicate that not only primary T cell responses, but also secondary T cell responses, highly depend on the lymphoid environment for effective activation.     

CCR6 Recruits Regulatory T Cells and Th17 Cells to the Kidney in Glomerulonephritis

T cells recruited to the kidney contribute to tissue damage in crescentic and proliferative glomerulonephritides. Chemokines and their receptors regulate T cell trafficking, but the expression profile and functional importance of chemokine receptors for renal CD4⁺ T cell subsets are incompletely understood. In this study, we observed that renal FoxP3⁺CD4⁺ regulatory T cells (Tregs) and IL-17–producing CD4⁺ T (Th17) cells express the chemokine receptor CCR6, whereas IFNγ-producing Th1 cells are CCR6⁻. Induction of experimental glomerulonephritis (nephrotoxic nephritis) in mice resulted in upregulation of the only CCR6 ligand, CCL20, followed by T cell recruitment, renal tissue injury, albuminuria, and loss of renal function. CCR6 deficiency aggravated renal injury and increased mortality (from uremia) among nephritic mice. Compared with wild-type (WT) mice, CCR6 deficiency reduced infiltration of Tregs and Th17 cells but did not affect recruitment of Th1 cells in the setting of glomerulonephritis. Adoptive transfer of WT but not CCR6-deficient Tregs attenuated morphologic and functional renal injury in nephritic mice. Furthermore, reconstitution with WT Tregs protected CCR6^−/− mice from aggravated nephritis. Taken together, these data suggest that CCR6 mediates renal recruitment of both Tregs and Th17 cells and that the reduction of anti-inflammatory Tregs in the presence of a fully functional Th1 response aggravates experimental glomerulonephritis.The currently defined four subsets of CD4⁺ T cells—namely Th1, Th2, Th17, and regulatory T cells (Tregs)—are central players in adaptive immunity.¹ Inappropriate or unbalanced T cell responses underlie several distinct types of autoimmune diseases, some of which target the kidney. In particular, infiltrating effector CD4⁺ T cells of the Th1 type are supposed to initiate and perpetuate glomerular and tubulointerstitial tissue damage in crescentic and proliferative forms of glomerulonephritis either directly by cytotoxic functions or cytokine secretion or indirectly by providing help for induction of autoantibodies and cytokines or immune complexes or by activating macrophages.² Another IL-17–producing CD4⁺ effector T cell subset, termed Th17, has been identified.³ Ongoing studies demonstrate that Th17 cells are involved in driving autoimmune processes previously thought to be exclusively Th1-mediated, such as rheumatoid arthritis,⁴ multiple sclerosis,⁵ and crescentic glomerulonephritis.^6,7 In contrast, the Th2 cell–mediated immune response seems to be of importance in nonproliferative forms of glomerulonephritis, such as minimal-change and membranous nephropathy.² In rodents and humans, a unique subset of CD4⁺CD25⁺FoxP3⁺ Tregs has been shown to control peripheral tolerance. An anti-inflammatory role of Tregs has also been suggested in human and experimental glomerulonephritis^8,9; however, the molecular basis of immunosuppression and the trafficking properties of Tregs are still unknown.Before T cells can exert their effects on renal damage or repair, they have to reach the site of injury. In recent years, it has become clear that a group of small proteins called chemokines serve as key regulators of directional T cell trafficking under inflammatory conditions.¹⁰ Target cell specificity is achieved by differential expression of corresponding chemokine receptors on the surface of leukocyte subsets. The different CD4⁺ T cell populations in humans and mice display distinct patterns of chemokine receptor expression. Th1-polarized cells preferentially express CXCR3, CCR5, and CXCR6, whereas Th2 cells express higher amounts of CCR3, CCR4, and CCR8.¹⁰ Although CCR6 and CXCR3 have been detected on Th17 cells,^11–13 the chemokine receptor expression profile of this subset has yet to be defined, particularly with respect to functional importance. Tregs with potential anti-inflammatory properties express a wider repertoire of chemokine receptors, many of which they share with proinflammatory T cell subsets, such as CCR4, CCR5, CCR6, CCR8, CXCR3, and CXCR6.^10,13 It remains unclear, however, which of these chemokine receptors (or which receptor combination) is crucial for guiding Tregs to the site of inflammation. In general, the precise molecular basis for the chemokine/chemokine receptor-mediated trafficking of CD4⁺ T cell subsets in glomerulonephritis is not defined.Several features of CCR6 and its only highly specific ligand CCL20 argue for a critical role of this chemokine–chemokine receptor pair in this context. CCR6 is expressed in human and mouse dendritic cell subpopulations,^14–16 B cells,^17,18 and T cell subsets.^13,19 Recent data suggest that, in particular, autoreactive Th17 cells, which contribute to renal tissue injury in nephritis, are highly CCR6⁺.^11,12 This study was designed to examine the potential role of CCR6 in glomerulonephritis. We therefore induced the T cell–dependent model of nephrotoxic nephritis (NTN) in wild-type (WT) and CCR6^−/− mice to address two major issues: (1) What is the expression pattern of CCR6 on infiltrating renal CD4⁺ T cell subsets? (2) Does CCR6 deficiency influence the clinical course of experimental glomerulonephritis, and, if so, what are the mechanisms?