Signal regulatory protein ? regulates the homeostasis of T lymphocytes in the spleen.
ABSTRACT: The molecular basis for formation of lymphoid follicle and its homeostasis in the secondary lymphoid organs remains unclear. Signal regulatory protein ? (SIRP?), an Ig superfamily protein that is predominantly expressed in dendritic cells or macrophages, mediates cell-cell signaling by interacting with CD47, another Ig superfamily protein. In this study, we show that the size of the T cell zone as well as the number of CD4(+) T cells were markedly reduced in the spleen of mice bearing a mutant (MT) SIRP? that lacks the cytoplasmic region compared with those of wild-type mice. In addition, the expression of CCL19 and CCL21, as well as of IL-7, which are thought to be important for development or homeostasis of the T cell zone, was markedly decreased in the spleen of SIRP? MT mice. By the use of bone marrow chimera, we found that hematopoietic SIRP? is important for development of the T cell zone as well as the expression of CCL19 and CCL21 in the spleen. The expression of lymphotoxin and its receptor, lymphotoxin ? receptor, as well as the in vivo response to lymphotoxin ? receptor stimulation were also decreased in the spleen of SIRP? MT mice. CD47-deficient mice also manifested phenotypes similar to SIRP? MT mice. These data suggest that SIRP? as well as its ligand CD47 are thus essential for steady-state homeostasis of T cells in the spleen.
Project description:The factors regulating growth and patterning of the spleen are poorly defined. We demonstrate here that spleens from B cell-deficient mice have 10-fold reduced expression of the T zone chemokine, CCL21, a threefold reduction in T cell and dendritic cell (DC) numbers, and reduced expression of the T zone stromal marker, gp38. Using cell transfer and receptor blocking approaches, we provide evidence that B cells play a critical role in the early postnatal development of the splenic T zone. This process involves B cell expression of lymphotoxin (LT)alpha1beta2, a cytokine that is required for expression of CCL21 and gp38. Introduction of a B cell specific LTalpha transgene on to the LTalpha-deficient background restored splenic CCL21 and gp38 expression, DC numbers, and T zone size. This work also demonstrates that the role of B cells in T zone development is distinct from the effect of B cells on splenic T cell numbers, which does not require LTalpha1beta2. Therefore, B cells influence spleen T zone development by providing: (a) signals that promote T cell accumulation, and: (b) signals, including LTalpha1beta2, that promote stromal cell development and DC accumulation. Defects in these parameters may contribute to the immune defects associated with B cell deficiency in mice and humans.
Project description:Rapid clearance of adoptively transferred Cd47-null (Cd47(-/-)) cells in congeneic WT mice suggests a critical self-recognition mechanism, in which CD47 is the ubiquitous marker of self, and its interaction with macrophage signal regulatory protein ? (SIRP?) triggers inhibitory signaling through SIRP? cytoplasmic immunoreceptor tyrosine-based inhibition motifs and tyrosine phosphatase SHP-1/2. However, instead of displaying self-destruction phenotypes, Cd47(-/-) mice manifest no, or only mild, macrophage phagocytosis toward self-cells except under the nonobese diabetic background. Studying our recently established Sirp?-KO (Sirp?(-/-)) mice, as well as Cd47(-/-) mice, we reveal additional activation and inhibitory mechanisms besides the CD47-SIRP? axis dominantly controlling macrophage behavior. Sirp?(-/-) mice and Cd47(-/-) mice, although being normally healthy, develop severe anemia and splenomegaly under chronic colitis, peritonitis, cytokine treatments, and CFA-/LPS-induced inflammation, owing to splenic macrophages phagocytizing self-red blood cells. Ex vivo phagocytosis assays confirmed general inactivity of macrophages from Sirp?(-/-) or Cd47(-/-) mice toward healthy self-cells, whereas they aggressively attack toward bacteria, zymosan, apoptotic, and immune complex-bound cells; however, treating these macrophages with IL-17, LPS, IL-6, IL-1?, and TNF?, but not IFN?, dramatically initiates potent phagocytosis toward self-cells, for which only the Cd47-Sirp? interaction restrains. Even for macrophages from WT mice, phagocytosis toward Cd47(-/-) cells does not occur without phagocytic activation. Mechanistic studies suggest a PKC-Syk-mediated signaling pathway, to which IL-10 conversely inhibits, is required for activating macrophage self-targeting, followed by phagocytosis independent of calreticulin Moreover, we identified spleen red pulp to be one specific tissue that provides stimuli constantly activating macrophage phagocytosis albeit lacking in Cd47(-/-) or Sirp?(-/-) mice.
Project description:Efficient immune defenses are facilitated by the organized microarchitecture of lymphoid organs, and this organization is regulated by the compartmentalized expression of lymphoid tissue chemokines. Mouse cytomegalovirus (MCMV) infection induces significant remodeling of splenic microarchitecture, including loss of marginal zone macrophage populations and dissolution of T and B cell compartmentalization. MCMV preferentially infected the splenic stroma, targeting endothelial cells (EC) as revealed using MCMV-expressing green fluorescent protein. MCMV infection caused a specific, but transient transcriptional suppression of secondary lymphoid chemokine (CCL21). The loss of CCL21 was associated with the failure of T lymphocytes to locate within the T cell zone, although trafficking to the spleen was unaltered. Expression of CCL21 in lymphotoxin (LT)-alpha-deficient mice is dramatically reduced, however MCMV infection further reduced CCL21 levels, suggesting that viral modulation of CCL21 was independent of LTalpha signaling. Activation of LTbeta-receptor signaling with an agonistic antibody partially restored CCL21 mRNA expression and redirected transferred T cells to the splenic T cell zone in MCMV-infected mice. These results indicate that virus-induced alterations in lymphoid tissues can occur through an LT-independent modulation of chemokine transcription, and targeting of the LT cytokine system can counteract lymphoid tissue remodeling by MCMV.
Project description:The inhibitory immunoreceptor SIRP? is expressed on myeloid and neuronal cells and interacts with the broadly expressed CD47. CD47-SIRP? interactions form an innate immune checkpoint and its targeting has shown promising results in cancer patients. Here, we report expression of SIRP? on B1 lymphocytes, a subpopulation of murine B cells responsible for the production of natural antibodies. Mice defective in SIRP? signaling (SIRP??CYT mice) displayed an enhanced CD11b/CD18 integrin-dependent B1 cell migration from the peritoneal cavity to the spleen, local B1 cell accumulation, and enhanced circulating natural antibody levels, which was further amplified upon immunization with T-independent type 2 antigen. As natural antibodies are atheroprotective, we investigated the involvement of SIRP? signaling in atherosclerosis development. Bone marrow (SIRP??CYT>LDLR-/-) chimaeric mice developed reduced atherosclerosis accompanied by increased natural antibody production. Collectively, our data identify SIRP? as a unique B1 cell inhibitory receptor acting to control B1 cell migration, and imply SIRP? as a potential therapeutic target in atherosclerosis.
Project description:The homeostatic control mechanisms regulating human leukocyte numbers are poorly understood. Here, we assessed the role of phagocytes in this process using human immune system (HIS) BALB/c Rag2(-/-)IL-2R?c(-/-) mice in which human leukocytes are generated from transplanted hematopoietic progenitor cells. Interactions between signal regulatory protein alpha (SIRP?; expressed on phagocytes) and CD47 (expressed on hematopoietic cells) negatively regulate phagocyte activity of macrophages and other phagocytic cells. We previously showed that B cells develop and survive robustly in HIS mice, whereas T and natural killer (NK) cells survive poorly. Because human CD47 does not interact with BALB/c mouse SIRP?, we introduced functional CD47/SIRP? interactions in HIS mice by transducing mouse CD47 into human progenitor cells. Here, we show that this procedure resulted in a dramatic and selective improvement of progenitor cell engraftment and human T- and NK-cell homeostasis in HIS mouse peripheral lymphoid organs. The amount of engrafted human B cells also increased but much less than that of T and NK cells, and total plasma IgM and IgG concentrations increased 68- and 35-fold, respectively. Whereas T cells exhibit an activated/memory phenotype in the absence of functional CD47/SIRP? interactions, human T cells accumulated as CD4(+) or CD8(+) single-positive, naive, resting T cells in the presence of functional CD47/SIRP? interactions. Thus, in addition to signals mediated by T cell receptor (TCR)/MHC and/or IL/IL receptor interactions, sensing of cell surface CD47 expression by phagocyte SIRP? is a critical determinant of T- and NK-cell homeostasis under steady-state conditions in vivo.
Project description:In secondary lymphoid organs, development and homeostasis of stromal cells such as podoplanin (Pdpn)-positive fibroblastic reticular cells (FRCs) are regulated by hematopoietic cells, but the cellular and molecular mechanisms of such regulation have remained unclear. Here we show that ablation of either signal regulatory protein ? (SIRP?), an Ig superfamily protein, or its ligand CD47 in conventional dendritic cells (cDCs) markedly reduced the number of CD4+ cDCs as well as that of Pdpn+ FRCs and T cells in the adult mouse spleen. Such ablation also impaired the survival of FRCs as well as the production by CD4+ cDCs of tumor necrosis factor receptor (TNFR) ligands, including TNF-?, which was shown to promote the proliferation and survival of Pdpn+ FRCs. CD4+ cDCs thus regulate the steady-state homeostasis of FRCs in the adult spleen via the production of TNFR ligands, with the CD47-SIRP? interaction in cDCs likely being indispensable for such regulation.
Project description:CD47 engagement by the macrophage signal regulatory protein alpha (SIRP?) inhibits phagocytic activity and protects red blood cells (RBCs) from erythrophagocytosis. The role of CD47-SIRP? in the innate immune response to Plasmodium falciparum infection is unknown. We hypothesized that disruption of SIRP? signaling may enhance macrophage uptake of malaria parasite-infected RBCs. To test this hypothesis, we examined in vivo clearance in CD47-deficient mice infected with Plasmodium berghei ANKA and in vitro phagocytosis of P. falciparum-infected RBCs by macrophages from SHP-1-deficient (Shp-1(-/-)) mice and NOD.NOR-Idd13.Prkdc(scid) (NS-Idd13) mice, as well as human macrophages, following disruption of CD47-SIRP? interactions with anti-SIRP? antibodies or recombinant SIRP?-Fc fusion protein. Compared to their wild-type counterparts, Cd47(-/-) mice displayed significantly lower parasitemia, decreased endothelial activation, and enhanced survival. Using macrophages from SHP-1-deficient mice or from NS-Idd13 mice, which express a SIRP? variant that does not bind human CD47, we showed that altered SIRP? signaling resulted in enhanced phagocytosis of P. falciparum-infected RBCs. Moreover, disrupting CD47-SIRP? engagement using anti-SIRP? antibodies or SIRP?-Fc fusion protein also increased phagocytosis of P. falciparum-infected RBCs. These results indicate an important role for CD47-SIRP? interactions in innate control of malaria and suggest novel targets for intervention.
Project description:CD47 is a widely expressed integral membrane protein that serves as the counter-receptor for the inhibitory phagocyte receptor signal-regulatory protein-? (SIRP?) and as a signaling receptor for the secreted matricellular protein thrombospondin-1. Recent studies employing mice and somatic cells lacking CD47 have revealed important pathophysiological functions of CD47 in cardiovascular homeostasis, immune regulation, resistance of cells and tissues to stress and chronic diseases of aging including cancer. With the emergence of experimental therapeutics targeting CD47, a more thorough understanding of CD47 signal transduction is essential. CD47 lacks a substantial cytoplasmic signaling domain, but several cytoplasmic binding partners have been identified, and lateral interactions of CD47 with other membrane receptors play important roles in mediating signaling resulting from the binding of thrombospondin-1. This review addresses recent advances in identifying the lateral binding partners, signal transduction pathways and downstream transcription networks regulated through CD47 in specific cell lineages. Major pathways regulated by CD47 signaling include calcium homeostasis, cyclic nucleotide signaling, nitric oxide and hydrogen sulfide biosynthesis and signaling and stem cell transcription factors. These pathways and other undefined proximal mediators of CD47 signaling regulate cell death and protective autophagy responses, mitochondrial biogenesis, cell adhesion and motility and stem cell self-renewal. Although thrombospondin-1 is the best characterized agonist of CD47, the potential roles of other members of the thrombospondin family, SIRP? and SIRP? binding and homotypic CD47 interactions as agonists or antagonists of signaling through CD47 should also be considered.
Project description:Abstract CD47 belongs to immunoglobulin superfamily and is widely expressed on the surface of cell membrane, while another transmembrane protein SIRP? is restricted to the surface of macrophages, dendritic cells, and nerve cells. As a cell surface receptor and ligand, respectively, CD47 and SIRP? interact to regulate cell migration and phagocytic activity, and maintain immune homeostasis. In recent years, studies have found that immunoglobulin superfamily CD47 is overexpressed widely across tumor types, and CD47 plays an important role in suppressing phagocytes activity through binding to the transmembrane protein SIRP? in phagocytic cells. Therefore, targeting CD47 may be a novel strategy for cancer immunotherapy, and a variety of anti-CD47 antibodies have appeared, such as humanized 5F9 antibody, B6H12 antibody, ZF1 antibody, and so on. This review mainly describes the research history of CD47-SIRP? and focuses on macrophage-mediated CD47-SIRP? immunotherapy of tumors.
Project description:Aim:Immunotherapies blocking the CD47-SIRP? pathway by targeting CD47 enhance macrophage phagocytosis of neoplastic cells in mouse models. As SIRP? exhibits relatively restricted tissue expression, SIRP? antagonists may be better tolerated than agents targeting CD47, which is ubiquitously expressed in many tissues. Here, we investigated the therapeutic impact of monoclonal antibodies (mAbs) against CD47 and/or SIRP? on gastroenterological tumors in syngeneic immunocompetent mouse models. Methods:We used in vitro and in vivo phagocytosis assays in C57BL/6J (B6) mice to investigate anti-CD47/SIRP? mAb effects on Hepa1-6 and CMT93 originating from B6 mice. The influence of these mAbs on macrophage transmigration was also assessed. To investigate anti-SIRP? mAb therapy-induced inhibitory effects on sporadic colon cancer growth, we used a CDX2P9.5-NLS Cre;APC + /FLOX (CPC-APC) mouse model. Results:Systemic anti-SIRP? mAb administration significantly increased Hepa1-6 and CMT93 cell susceptibility to macrophage phagocytosis, both in vitro and in vivo. Conversely, similarly administered anti-CD47 mAb did not promote macrophage phagocytosis of target cells, whereas cells incubated with anti-CD47 mAb prior to inoculation were more susceptible to macrophage phagocytosis. In vitro cell migration assays revealed that binding with anti-CD47 mAb inhibited macrophage transmigration. Anti-SIRP? mAb treatment inhibited tumor progression in CPC-APC mice and significantly improved overall survival. Anti-CD47 mAb administration in vivo eliminated the phagocytosis-promoting CD47 blockade effect, probably by inhibiting macrophage transmigration/chemotaxis. In contrast, anti-SIRP? mAb exhibited enhanced macrophage phagocytic activity and marked anti-tumor effects against gastroenterological malignancies. Conclusion:SIRP? mAb augmentation of macrophage phagocytic activity may represent an effective treatment strategy for human gastrointestinal tumors.