133 research outputs found
Protein-tyrosine Phosphatase Shp2 Positively Regulates Macrophage Oxidative Burst
Macrophages are vital to innate immunity and express pattern recognition receptors and integrins for the rapid detection of invading pathogens. Stimulation of Dectin-1 and complement receptor 3 (CR3) activates Erk- and Akt-dependent production of reactive oxygen species (ROS). Shp2, a protein-tyrosine phosphatase encoded by Ptpn11, promotes activation of Ras-Erk and PI3K-Akt and is crucial for hematopoietic cell function; however, no studies have examined Shp2 function in particulate-stimulated ROS production. Maximal Dectin-1-stimulated ROS production corresponded kinetically to maximal Shp2 and Erk phosphorylation. Bone marrow-derived macrophages (BMMs) from mice with a conditionally deleted allele of Ptpn11 (Shp2flox/flox;Mx1Cre+) produced significantly lower ROS levels compared with control BMMs. Although YFP-tagged phosphatase dead Shp2-C463A was strongly recruited to the early phagosome, its expression inhibited Dectin-1- and CR3-stimulated phospho-Erk and ROS levels, placing Shp2 phosphatase function and Erk activation upstream of ROS production. Further, BMMs expressing gain of function Shp2-D61Y or Shp2-E76K and peritoneal exudate macrophages from Shp2D61Y/+;Mx1Cre+ mice produced significantly elevated levels of Dectin-1- and CR3-stimulated ROS, which was reduced by pharmacologic inhibition of Erk. SIRPĪ± (signal regulatory protein Ī±) is a myeloid inhibitory immunoreceptor that requires tyrosine phosphorylation to exert its inhibitory effect. YFP-Shp2C463A-expressing cells have elevated phospho-SIRPĪ± levels and an increased Shp2-SIRPĪ± interaction compared with YFP-WT Shp2-expressing cells. Collectively, these findings indicate that Shp2 phosphatase function positively regulates Dectin-1- and CR3-stimulated ROS production in macrophages by dephosphorylating and thus mitigating the inhibitory function of SIRPĪ± and by promoting Erk activation
Signal regulatory protein alpha blockade potentiates tumoricidal effects of macrophages on gastroenterological neoplastic cells in syngeneic immunocompetent mice
Aim: Immunotherapies blocking the CD47-SIRP alpha pathway by targeting CD47 enhance macrophage phagocytosis of neoplastic cells in mouse models. As SIRP alpha exhibits relatively restricted tissue expression, SIRP alpha 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 alpha on gastroenterological tumors in syngeneic immunocompetent mouse models.Methods: We used in vitro and in vivo phagocytosis assays in C57B1J6J (B6) mice to investigate anti-CD47/SIRP alpha mAb effects on Hepal-6 and CMT93 originating from B6 mice. The influence of these mAbs on macrophage transmigration was also assessed. To investigate anti-SIRP alpha mAb therapy-induced inhibitory effects on sporadic colon cancer growth, we used a CDX2P9.5-NLS Cre:APC7FLOX (CPC-APC) mouse model.Results: Systemic anti-SIRP alpha mAb administration significantly increased Hepal-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 alpha 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 alpha mAb exhibited enhanced macrophage phagocytic activity and marked anti-tumor effects against gastroenterological malignancies.Conclusion: SIRP alpha mAb augmentation of macrophage phagocytic activity may represent an effective treatment strategy for human gastrointestinal tumors.</p
Preclinical evaluation of the efficacy of an antibody to human SIRPĪ± for cancer immunotherapy in humanized mouse models
Tumor-associated macrophages (TAMs) are abundant in the tumor microenvironment and are considered potential targets for cancer immunotherapy. To examine the antitumor effects of agents targeting human TAMs in vivo, we here established preclinical tumor xenograft models based on immunodeficient mice that express multiple human cytokines and have been reconstituted with a human immune system by transplantation of human CD34 hematopoietic stem and progenitor cells (HIS-MITRG mice). HIS-MITRG mice supported the growth of both human cell line (Raji)- and patient-derived B cell lymphoma as well as the infiltration of human macrophages into their tumors. We examined the potential antitumor action of an antibody to human SIRPĪ± (SE12C3) that inhibits the interaction of CD47 on tumor cells with SIRPĪ± on human macrophages and thereby promotes FcĪ³ receptor-mediated phagocytosis of the former cells by the latter. Treatment with the combination of rituximab (antibody to human CD20) and SE12C3 inhibited Raji tumor growth in HIS-MITRG mice to a markedly greater extent than did rituximab monotherapy. This enhanced antitumor effect was dependent on human macrophages and attributable to enhanced rituximab-dependent phagocytosis of lymphoma cells by human macrophages. Treatment with rituximab and SE12C3 also induced reprogramming of human TAMs toward a proinflammatory phenotype. Furthermore, the combination treatment essentially prevented the growth of patient-derived diffuse large B cell lymphoma in HIS-MITRG mice. Our findings thus support the study of HIS-MITRG mice as a model for the preclinical evaluation in vivo of potential therapeutics, such as antibodies to human SIRPĪ±, that target human TAMs
Prion pathogenesis is unaltered in the absence of SIRPĪ±-mediated "don't-eat-me" signaling
Prion diseases are neurodegenerative conditions caused by misfolding of the prion protein, leading to conspicuous neuronal loss and intense microgliosis. Recent experimental evidence point towards a protective role of microglia against prion-induced neurodegeneration, possibly through elimination of prion-containing apoptotic bodies. The molecular mechanisms by which microglia recognize and eliminate apoptotic cells in the context of prion diseases are poorly defined. Here we investigated the possible involvement of signal regulatory protein Ī± (SIRPĪ±), a key modulator of host cell phagocytosis; SIRPĪ± is encoded by the Sirpa gene that is genetically linked to the prion gene Prnp. We found that Sirpa transcripts are highly enriched in microglia cells within the brain. However, Sirpa mRNA levels were essentially unaltered during the course of experimental prion disease despite upregulation of other microglia-enriched transcripts. To study the involvement of SIRPĪ± in prion pathogenesis in vivo, mice expressing a truncated SIRPĪ± protein unable to inhibit phagocytosis were inoculated with rodent-adapted scrapie prions of the 22L strain. Homozygous and heterozygous Sirpa mutants and wild-type mice experienced similar incubation times after inoculation with either of two doses of 22L prions. Moreover, the extent of neuronal loss, microgliosis and abnormal prion protein accumulation was not significantly affected by Sirpa genotypes. Collectively, these data indicate that SIRPĪ±-mediated phagocytosis is not a major determinant in prion disease pathogenesis. It will be important to search for additional candidates mediating prion phagocytosis, as this mechanism may represent an important target of antiprion therapies
<b>PROTEIN KINASE C REGULATES SOMATOSTATIN BINDING TO ITS RECEPTORS ON RAT PANCREATIC ACINAR CELL </b><b>MEMBRANES </b>
The Role of Type-2 Conventional Dendritic Cells in the Regulation of Tumor Immunity
Conventional dendritic cells (cDCs) orchestrate immune responses to cancer and comprise two major subsets: type-1 cDCs (cDC1s) and type-2 cDCs (cDC2s). Compared with cDC1s, which are dedicated to the activation of CD8+ T cells, cDC2s are ontogenically and functionally heterogeneous, with their main function being the presentation of exogenous antigens to CD4+ T cells for the initiation of T helper cell differentiation. cDC1s play an important role in tumor-specific immune responses through cross-presentation of tumor-derived antigens for the priming of CD8+ T cells, whereas little is known of the role of cDC2s in tumor immunity. Recent studies have indicated that human cDC2s can be divided into at least two subsets and have implicated these cells in both anti- and pro-tumoral immune responses. Furthermore, the efficacy of cDC2-based vaccines as well as cDC2-targeted therapeutics has been demonstrated in both mouse models and human patients. Here we summarize current knowledge about the role of cDC2s in tumor immunity and address whether these cells are beneficial in the context of antitumor immune responses
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