Regulation of Immune Responses by the Activating and Inhibitory Myeloid-Associate Immunoglobuline-Like Receptors (MAIR) (CD300)

Development of Monoclonal Antibodies Specific to Either CD300AR111 or CD300AQ111 or Both

CD300A is a member of the CD300 immunoglobulin (Ig)-like receptor family consisting of eight molecules in humans, all of which contain one Ig-like domain in the extracellular portion. Upon binding its ligand phosphatidylserine or phosphatidylethanolamine, CD300A mediates an inhibitory signal through the immunoreceptor tyrosine-based inhibitory motif in the cytoplasmic portion. The CD300 family molecules are highly homologous to each other. In addition, CD300A has a single nucleotide polymorphism (rs2272111), which is a nonsense mutation encoding glutamine (CD300AQ111) instead of arginine (CD300AR111) at residue 111 in the Ig-like domain of CD300A. In this study, we successfully generated monoclonal antibodies (mAbs) specific to either CD300AR111 or CD300AQ111 or both. These mAbs are useful for the analysis of CD300A genotype by flow cytometry and the development of an antibody drug for the treatment of various diseases.

The interaction of CD300lf and ceramide reduces the development of periodontitis by inhibiting osteoclast differentiation

AIM

The regulation of osteoclasts (OCs) by inhibitory immunoreceptors maintains bone homeostasis and is considered an important determinant of the extent of periodontal pathology. The aim of this study was to investigate the role of the inhibitory immunoreceptor CD300lf and its ligand ceramide in osteoclastogenesis in periodontitis.

MATERIALS AND METHODS

The expression of CD300lf was measured in vitro and in a ligature-induced periodontitis model. The effect of CD300lf ablation on osteoclastogenesis was examined in ligature-retained and ligature removal periodontitis models. The effect of ceramide, the ligand of CD300lf, was examined in osteoclastogenesis in vitro and in vivo by smearing 20 μg of ceramide dissolved in carboxymethylcellulose on teeth and gingiva every other day in an experimental periodontitis model and ligature removal model.

RESULTS

CD300lf expression was downregulated during osteoclastogenesis. Ablation of CD300lf in the ligature-induced periodontitis model increased the number of OCs and exacerbated bone damage. Bone resorption caused by CD300lf ablation was reversible following ligature removal. CD300lf-ceramide binding suppressed osteoclastogenesis in vitro and inhibited alveolar bone loss in a mouse periodontitis model.

CONCLUSIONS

Our findings reveal that CD300lf-ceramide binding plays a critical negative role in alveolar bone loss in periodontitis by inhibiting OCs differentiation.

CD300a Receptor Blocking Enhances Early Clearance of Leishmania donovani From Its Mammalian Host Through Modulation of Effector Functions of Phagocytic and Antigen Experienced T Cells

The parasites of the genus Leishmania survive and proliferate in the host phagocytic cells by taking control over their microbicidal functions. The parasite also promotes differentiation of antigen-specific anti-inflammatory cytokines producing effector T cells, which eventually results in disease pathogenesis. The mechanisms that parasites employ to dominate host adaptive immunity are largely unknown. For the first time, we report that L. donovani, which causes visceral leishmaniasis in the Indian subcontinent, upregulates the expression of an immune inhibitory receptor i.e., CD300a on antigen presenting and phagocytic cells to dampen their effector functions. The blocking of CD300a signals in leishmania antigens activated macrophages and dendritic cells enhanced the production of nitric oxide, pro-inflammatory cytokines along with MHCI/II genes expression, and reduced parasitic uptake. Further, the abrogation of CD300a signals in Leishmania infected mice benefited antigen-experienced, i.e., CD4⁺CD44⁺ and CD8⁺CD44⁺ T cells to acquire more pro-inflammatory cytokines producing phenotypes and helped in the early clearance of parasites from their visceral organs. The CD300a receptor blocking also enhanced the conversion of CD4⁺ T effectors cells to their memory phenotypes i.e., CCR7^high CD62L^high up to 1.6 and 1.9 fold after 14 and 21 days post-infection, respectively. These findings implicate that CD300a is an important determinant of host phagocytic cells functions and T cells differentiation against Leishmania antigens.

CD300a blockade enhances efferocytosis by infiltrating myeloid cells and ameliorates neuronal deficit after ischemic stroke

[Figure: see text].

The ubiquitous role of spleen tyrosine kinase (Syk) in gut diseases: From mucosal immunity to targeted therapy

Spleen tyrosine kinase (Syk) is a cytoplasmic non-receptor protein tyrosine kinase expressed in a variety of cells and play crucial roles in signal transduction. Syk mediates downstream signaling by recruiting to the dually phosphorylated immunoreceptor tyrosine-based activation motifs (ITAMs) of the transmembrane adaptor molecule or the receptor chain itself. In gut diseases, Syk is observed to be expressed in intestinal epithelial cells, monocytes/macrophages, dendritic cells and mast cells. Activation of Syk in these cells can modulate intestinal mucosal immune response by promoting inflammatory cytokines and chemokines production, thus regulating gut homeostasis. Due to the restriction of specificity and selectivity for the development of Syk inhibitors, only a few such inhibitors are available in gut diseases, including intestinal ischemia/reperfusion damage, infectious disease, inflammatory bowel disease, etc. The promising outcomes of Syk inhibitors from both preclinical and clinical studies have shown to attenuate the progression of gut diseases thereby indicating a great potential in the development of Syk targeted therapy for treatment of gut diseases. This review depicts the characterization of Syk, summarizes the signal pathways of Syk, and discusses its potential targeted therapy for gut diseases.

The role of NK cells in fighting the virus infection and sepsis

Natural killer cells, one of the important types of innate immune cells, play a pivotal role in the antiviral process in vivo. It has been shown that increasing NK cell activity may promote the alleviation of viral infections, even severe infection-induced sepsis. Given the current state of the novel coronavirus (SARS-CoV-2) global pandemic, clarifying the anti-viral function of NK cells would be helpful for revealing the mechanism of host immune responses and decipher the progression of COVID-19 and providing important clues for combating this pandemic. In this review, we summarize the roles of NK cells in viral infection and sepsis as well as the potential possibilities of NK cell-based immunotherapy for treating COVID-19.

Nrf2 activation mediates tumor-specific hepatic stellate cells-induced DIgR2 expression in dendritic cells

Our previous studies discovered that tumor-specific hepatic stellate cells (tHSCs) induced dendritic cell-derived immunoglobulin receptor 2 (DIgR2) expression in bone marrow-derived dendritic cells (mDCs), inhibiting splenic T cell activation. The current study aims to explore the underlying mechanism of DIgR2 expression by focusing on Nrf2 (nuclear-factor-E2-related factor 2) signaling. We show that tHSCs co-culture induced significant Nrf2 signaling activation in mDCs. The latter was evidenced by Nrf2-Keap1 disassociation, Nrf2 protein stabilization, accumulation and nuclear translocation. Expression of Nrf2-dependent genes, including heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1), were detected in tHSCs-co-cultured mDCs. Importantly tHSCs-induced DIgR2 expression was blocked by Nrf2 shRNA or knockout (KO, by CRISPR/Cas9 method). Conversely, forced activation of Nrf2, by Keap1 shRNA or the Nrf2 activators (3H-1,2-dithiole-3-thione and MIND4-17), induced significant DIgR2 expression. tHSCs stimulation induced reactive oxygen species (ROS) production in mDCs. Conversely, ROS scavengers inhibited tHSCs-induced ROS production, Nrf2 activation and DIgR2 expression in mDCs. Significantly, tHSCs inhibited production of multiple cytokines (CD80, CD86 and IL-12) in mDCs, reversed by Nrf2 depletion. Moreover, Nrf2 shRNA or KO attenuated splenic T cell inhibition by tHSCs-stimulated mDCs. Together, we conclude that Nrf2 activation mediates tHSCs-induced DIgR2 expression in mDCs.

DlgR2 knockdown boosts dendritic cell activity and inhibits hepatocellular carcinoma tumor in-situ growth

Tumor-specific hepatic stellate cells (tHSCs) positively participate in human hepatocellular carcinoma (HCC) tumorigenesis and progression. Our previous studies have shown that tHSCs co-culture with dendritic cells (DCs) induced DIgR2 (dendritic cell-derived immunoglobulin receptor 2) expression. The latter is a member of IgSF inhibitory receptor suppressing DCs-initiated antigen-specific T-cell responses. In the current study, we show that hepatic artery injection of DlgR2 siRNA significantly inhibited in-situ HCC xenograft growth in rat livers. Further, 5-FU-medied inhibition of in-situ HCC growth was dramatically sensitized with DlgR2 silence. DlgR2 siRNA injection indeed downregulated DlgR2 in ex-vivo cultured tumor-derived DCs (tDCs). More importantly, tDCs activity was boosted following DlgR2 siRNA. These cells presented with upregulated CD80, CD86 and MHC-II. Production of interleukin-12 and tumor necrosis factor-α was also increased in the DlgR2-silenced tDCs. We propose that DlgR2 knockdown likely boosts the activity of tumor-associated DCs, and inhibits growth of in-situ HCC xenografts.

The Biology and Disease Relevance of CD300a, an Inhibitory Receptor for Phosphatidylserine and Phosphatidylethanolamine

The CD300a inhibitory receptor belongs to the CD300 family of cell surface molecules that regulate a diverse array of immune cell processes. The inhibitory signal of CD300a depends on the phosphorylation of tyrosine residues embedded in ITIMs of the cytoplasmic tail. CD300a is broadly expressed on myeloid and lymphoid cells, and its expression is differentially regulated depending on the cell type. The finding that CD300a recognizes phosphatidylserine and phosphatidylethanolamine, two aminophospholipids exposed on the outer leaflet of dead and activated cells, has shed new light on its role in the modulation of immune functions and in its participation in the host response to several diseases states, such as infectious diseases, cancer, allergy, and chronic inflammatory diseases. This review summarizes the literature on CD300a expression, regulation, signaling pathways, and ligand interaction, as well as its role in fine tuning immune cell functions and its clinical relevance.

Identification and Characterization of CD300H, a New Member of the Human CD300 Immunoreceptor Family

Recruitment of circulating monocytes and neutrophils to infection sites is essential for host defense against infections. Here, we identified a previously unannotated gene that encodes an immunoglobulin-like receptor, designated CD300H, which is located in the CD300 gene cluster. CD300H has a short cytoplasmic tail and associates with the signaling adaptor proteins, DAP12 and DAP10. CD300H is expressed on CD16(+) monocytes and myeloid dendritic cells. Ligation of CD300H on CD16(+) monocytes and myeloid dendritic cells with anti-CD300H monoclonal antibody induced the production of neutrophil chemoattractants. Interestingly, CD300H expression varied among healthy subjects, who could be classified into two groups according to "positive" and "negative" expression. Genomic sequence analysis revealed a single-nucleotide substitution (rs905709 (G → A)) at a splice donor site on intron 1 on either one or both alleles. The International HapMap Project database has demonstrated that homozygosity for the A allele of single nucleotide polymorphism (SNP) rs905709 ("negative" expression) is highly frequent in Han Chinese in Beijing, Japanese in Tokyo, and Europeans (A/A genotype frequencies 0.349, 0.167, and 0.138, respectively) but extremely rare in Sub-Saharan African populations. Together, these results suggest that CD300H may play an important role in innate immunity, at least in populations that carry the G/G or G/A genotype of CD300H.

Involvement of CD300a Phosphatidylserine Immunoreceptor in Aluminum Salt Adjuvant-Induced Th2 Responses

Aluminum salt (alum) has been widely used for vaccinations as an adjuvant. Alum not only enhances immunogenicity but also induces Th2 cell immune responses. However, the mechanisms of how alum enhances Th2 cell immune responses have been controversial. In an experimental allergic airway inflammation model, in which alum in conjunction with OVA Ag was i.p. injected for immunization, we found that apoptotic cells and inflammatory dendritic cells (iDC) expressing CD300a, an inhibitory immunoreceptor for phosphatidylserine (PS), significantly increased in number in the peritoneal cavity after the immunization. In contrast, apoptotic cells and iDCs were scarcely observed in the peritoneal cavity after injection of OVA alone. In CD300a-deficient mice, eosinophil infiltration in bronchoalveolar lavage fluid, serum IgE levels, and airway hyperreactivity were significantly decreased after immunization with alum plus OVA compared with wild-type mice. In vitro, iDCs purified from CD300a-deficient mice after the immunization induced significantly less IL-4 production from OT-II naive CD4(+) T cells after coculture with OVA Ag. CD300a expressed on iDCs bound PS on apoptotic cells in the peritoneal cavity after injection of OVA plus alum. Blocking CD300a interaction with PS by injection of a neutralizing anti-CD300a Ab resulted in inhibition of the development of allergic airway inflammation. These results suggest that CD300a is involved in alum-induced Th2 skewing.

The role of natural cytotoxicity receptors in various pathologies: emphasis on type I diabetes

Natural killer (NK) cells are innate immune lymphocytes that function mainly as immune sentinels against viral infection and tumorigenesis. NK cell function is governed by inhibitory and activating signals arising from corresponding receptors. A prominent group of activating NK receptors is the natural cytotoxicity receptors (NCRs), which includes NKp30, NKp44, and NKp46. These receptors bind various diverse ligands of pathogenic, tumor, and even self origin. Type 1 diabetes mellitus (T1D) is a multifactorial autoimmune disease, in which insulin-producing beta (β) cells are ablated by the immune system. This killing of β cells is carried out mainly by T cells, but many other immune cells have been implicated in the pathogenesis of this disease. Importantly, NK cells were shown to be key participants in the initial autoimmune attack. It was shown that all β cells from humans and mice, healthy or sick, express an unknown ligand for the activating NKp46 receptor. In this review, we describe the role played by the NCRs in various pathologies with an emphasis on Type I diabetes.

SHPS-1 and a synthetic peptide representing its ITIM inhibit the MyD88, but not TRIF, pathway of TLR signaling through activation of SHP and PI3K in THP-1 cells

BACKGROUND

Src homology 2 domain-containing protein tyrosine phosphatase substrate (SHPS)-1 is known to have regulatory effects on myeloid cells. However, its role in macrophage activation is not clearly understood.

METHODS AND RESULTS

In order to investigate the role of SHPS-1 in Toll-like receptor (TLR)-mediated activation, human monocytic cell lines were treated with anti-SHPS-1 monoclonal antibody. The triggering of SHPS-1 blocked the expression of IL-8 and TNF-α in cells treated with a TLR4 ligand that induces a signaling pathway involving myeloid differentiation factor 88 (MyD88) and Toll-interleukin-1 receptor (TIR)-domain-containing adapter-inducing interferon-β (TRIF). Interestingly, SHPS-1 inhibited TLR9/MyD88-mediated, but not TLR3/TRIF-mediated, expression of IL-8. Accordingly, a synthetic peptide representing the immunoreceptor tyrosine-based inhibition motif (ITIM) of SHPS-1 suppressed only the MyD88 pathway. Utilization of specific inhibitors and Western blot analysis indicated that the inhibitory effects were mediated by Src homology 2 domain-containing phosphatases (SHPs) and phosphoinositide 3-kinase (PI3K).

CONCLUSION

SHPS-1 negatively regulates the MyD88-dependent TLR signaling pathway through the inhibition of NF-κB activation.

Synthetic peptides containing ITIM-like domains block expression of inflammatory mediators and migration/invasion of cancer cells through activation of SHP-1 and PI3K

Increasing evidence supports that inflammation is closely associated with the development of cancer. In an effort to develop synthetic peptides that can suppress the inflammatory activation of cancer cells, decapeptides representing immunoreceptor tyrosine-based inhibitory motif (ITIM)-like sequences of immune receptor expressed on myeloid cells-1 (IREM-1) were tested for their anti-inflammatory effects in cancer cell lines. One (named TAT-YADL) out of the five synthetic peptides tested exhibited inhibitory effects on the expression of inflammatory mediators as well as invasion and migration. The inhibitory activities of the synthetic peptides required activation of SH2-containing protein tyrosine phosphatase-1 (SHP-1) and phosphoinositide 3-kinase (PI3K).

Synthetic peptides containing ITIM-like sequences of IREM-1 (CD300F) differentially regulate MyD88 and TRIF-mediated TLR signalling through activation of SHP and/or PI3K

The immune receptor expressed on myeloid cells 1 (IREM-1/CD300F) has been shown to inhibit various inflammatory processes in myeloid cells, such as macrophages and mast cells. IREM-1 exerts its inhibitory effect through its intracellular immunoreceptor tyrosine-based inhibition motifs (ITIMs). In order to generate immunomodulatory molecules that can regulate the inflammatory activation of macrophages, decapeptides representing each of the five ITIM-like sequences in the cytoplasmic tail of IREM-1 were synthesized in conjugation with human immunodeficiency virus-transactivator of transcription (HIV-TAT(48-57)), which was added to promote internalization of the peptides. Interestingly, all these TAT-ITIM fusion peptides inhibited Toll-like receptor (TLR)-mediated production of proinflammatory molecules, including matrix metalloproteinase (MMP)-9, tumour necrosis factor (TNF)-α, monocyte chemotactic protein-1 (MCP-1) and interleukin (IL)-8. When various TLR ligands were used to stimulate the human macrophage-like cell line human acute monocytic leukaemia cell line (THP)-1, the TAT-ITIM peptides blocked both myeloid differentiation factor 88 (MyD88) and Toll-interleukin 1 receptor (TIR)-domain-containing adapter-inducing interferon-β (TRIF)-mediated TLR signalling pathways. Utilization of specific inhibitors and detection of the active form of signalling adaptors by Western blot analysis further demonstrated that the inhibitory effects of these TAT-ITIM peptides require activation of Src homology 2 (SH2)-containing tyrosine phosphatase (SHP) and/or phosphoinositide 3-kinase (PI3K). These data indicate that these synthetic peptides may be used to regulate immune responses that involve TLR-mediated inflammatory activation of macrophages.

CD300a and CD300f differentially regulate the MyD88 and TRIF-mediated TLR signalling pathways through activation of SHP-1 and/or SHP-2 in human monocytic cell lines

CD300a, a membrane protein expressed on myeloid lineages and specific subsets of CD4(+) T cells, has been reported to have inhibitory activities in cellular activation. However, the role of CD300a in Toll-like receptor (TLR) -mediated macrophage activation has not been investigated. The human monocytic cell lines THP-1 and U937 were stimulated with various TLR ligands after triggering of CD300a with specific monoclonal antibody. Interestingly, CD300a blocked TLR4-mediated and TLR9-mediated expression of pro-inflammatory mediators without affecting TLR3-mediated events. In contrast, CD300f, another member of the CD300 family, blocked the activation of cells induced by all TLR ligands. A transient transfection assay using luciferase reporter gene under the regulation of nuclear factor-κB binding sites indicated that co-transfection of CD300f blocked reporter expression induced by over-expression of both myeloid differentiation factor 88 (MyD88) and toll-interleukin 1 receptor-domain-containing adapter-inducing interferon-β (TRIF), whereas CD300a blocked only MyD88-induced events. Synthetic peptides representing immunoreceptor tyrosine-based inhibitory motifs of CD300a or CD300f mimicked the differential inhibition patterns of their original molecules. The use of various signalling inhibitors and Western blotting analysis revealed that TLR9/MyD88-mediated signalling was regulated mainly by SH2-containing tyrosine phosphatase 1 (SHP-1), which could be activated by CD300a or CD300f. In contrast, regulation of the TLR3/TRIF-mediated pathway required the combined action of SHP-1 and SHP-2, which could be accomplished by CD300f but not CD300a. These data indicate that CD300a and CD300f regulate the MyD88 and TRIF-mediated TLR signalling pathways through differential activation of SHP-1 and SHP-2.

Synthetic peptides containing ITIM-like sequences of IREM-1 inhibit BAFF-mediated regulation of interleukin-8 expression and phagocytosis through SHP-1 and/or PI3K

B-cell activation factor of the tumour necrosis factor family (BAFF), an important regulator of B-cell survival, has recently been found to be expressed on the surface of murine and human macrophages and engagement with its receptor was shown to trigger induction of pro-inflammatory mediators and block phagocytic activity. In an effort to generate immunomodulatory agents that can regulate BAFF-mediated signal, decapeptides representing the intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIMs) of immune receptor expressed on myeloid cells (IREM)-1, an inhibitory transmembrane protein expressed on myeloid cells, were synthesized in conjugation with HIV-transactivator of transcription (TAT)(48-57,) which facilitates the internalization of peptides into cells. Interestingly, all five of these synthetic peptides, representing the five ITIM-like sequences present in the cytoplasmic tail of IREM-1, exhibited inhibitory action against BAFF-mediated induction of matrix metalloproteinase-9 and interleukin-8 expression. Inhibitor assay and immunoprecipitation assay followed by Western blotting demonstrated that the inhibitory action was mediated by Src homology 2 (SH2)-containing tyrosine phosphatase (SHP)-1 and/or phosphoinositide 3-kinase (PI3K). ELISA-based nuclear factor-κB DNA binding assay observed that the synthetic peptides blocked the activation of nuclear factor-κB in an SHP-1 and phosphoinositide 3-kinase-dependent manner. Three of these synthetic peptides exhibited varying degrees of inhibitory action against BAFF-mediated blockage of phagocytosis in a SHP-1 and PI3K-dependent manner. These data indicate that the synthetic peptides are capable of blocking BAFF-mediated regulation of macrophage activities through the activation of SHP-1 and PI3K as well as inhibition of nuclear factor-κB activation.

CD300F blocks both MyD88 and TRIF-mediated TLR signaling through activation of Src homology region 2 domain-containing phosphatase 1

CD300F is known to exhibit inhibitory activity in myeloid cells through its intracellular ITIM. To investigate the effect of CD300F stimulation on TLR signaling, the human acute monocytic leukemia cell line THP-1 was treated with CD300F-specific mAbs or two synthetic peptides that represented the ITIM-like domains of CD300F. Treatment with these agents blocked TLR2-, 3-, 4-, and 9-mediated expression of proinflammatory mediators such as IL-8 and matrix metalloproteinase-9. The luciferase reporter assay in 293T cells and Western blot analysis of THP-1 cells revealed that these inhibitory actions were effective in pathways involving MyD88 and/or TRIF of TLR signaling and associated with marked suppression of IκB kinase activation, phosphorylation/degradation of IκB, and subsequent activation of NF-κB. Use of specific inhibitors and immunoprecipitation analysis further indicated that the inhibitory effects were mediated by Src homology 2 domain-containing phosphatase-1, a protein tyrosine phosphatase with inhibitory activity in hematopoietic cells. These data indicate that CD300F is an active regulator of TLR-mediated macrophage activation through its association with Src homology 2 domain-containing phosphatase-1 and that the synthetic peptides can be applied for the regulation of immune responses that are induced by TLRs.

[Characteristics of peripheral rheograms following thermal provocation in normal and pathologic pregnancy]

Using the impedance plethysmographic method of rheography it is possible to ascertain the tone of the peripheral resistance vessels directly by simple means. Previous studies have shown that there is a close relationship between peripheral vasodilatation at rest and normal course of pregnancy. In the present study, rheographic changes were studied in patients with normal pregnancy (n = 27, Group 1), diabetes mellitus (n = 18, Group 2), "pregnancy-induced hypertension" (n = 10, Group 3), and chronic placental insufficiency (n = 16, Group 4) during and following a low-temperature stimulus. After exposure to icy water, the Group 1 subjects showed a 40% reduction in rheographic amplitude, Groups 2 and 3 a 25% reduction, while Group 4 patients showed no signs of vasoconstriction going beyond the resting state (p less than 0.001). The four groups also differed considerably as regards vessel wall behavior in the recovery phase. The study confirms that the amplitude of the peripheral rheogram is a good indicator for detecting high-risk pregnancies. The amplitude pattern under thermal stimulation also provides further information on the dynamic behavior of the resistance vessels in normal and pathologic pregnancies.