3, ?,44). We show that LILRA2 cross-linking on monocytes prior to LPS stimulation, or simultaneous activation through LILRA2 and TLR4, significantly reduced production of pro-inflammatory cytokines and IL-12 (Fig. and IFN compared to those stimulated with LPS. Furthermore, cross-linking of LILRA2 on monocytes significantly decreased phagocytosis of IgG-coated micro-beads and serum opsonized but had limited effect on phagocytosis of non-opsonized bacteria. Simultaneous co-stimulation of monocytes through LILRA2 and LPS or sequential activation of monocytes through LILRA2 followed by LPS led lower levels of TNF, IL-1 and IL-12 production compared to LPS alone, but had Rabbit Polyclonal to COMT additive effect on levels of IL-10 and IFN but not on IL-6. Interestingly, LILRA2 cross-linking on monocytes caused significant inhibition of TLR4 mRNA and protein, suggesting LILRA2-mediated suppression of LPS responses might be partly via regulation of this receptor. Taken Alcaftadine together, we provide evidence that LILRA2-mediated Alcaftadine activation of monocytes is significantly different to LPS and that LILRA2 selectively modulates LPS-mediated monocyte activation and FcRI-dependent phagocytosis. Introduction The leukocyte immunoglobulin-like receptor A2 (LILRA2) belongs to a highly homologous family of activating and inhibitory receptors constitutively expressed on the surface of leukocytes , . LILRA2 is an activating receptor which is preferentially expressed on monocytes, macrophages, neutrophils, eosinophils and basophils C, but not on lymphocytes or NK cells, suggesting that this receptor may play a role in the innate immune responses. LILRA2 contains a short cytoplasmic tail and a highly charged transmembrane website that associates with the common gamma chain of the Fc receptor (FcR) and transduces activation signals via an immunoreceptor tyrosine-based activating motif (ITAM) . Cross-linking of LILRA2 on the surface of leukocytes recruits protein tyrosine kinase signaling molecules that lead to cellular activation . On monocytes, engagement of LILRA2 causes calcium influx and improved production of pro-inflammatory cytokines , , . Similarly, cross-linking of LILRA2 on the surface of eosinophils and basophils causes significant degranulation of these cells and improved production of pro-inflammatory mediators and immune regulatory cytokines suggesting that it may play a role in modulation of inflammatory reactions , . This is supported by findings of extensive manifestation of LILRA2 protein on the surface of macrophages in synovial cells of individuals with active rheumatoid arthritis  and on the skin of individuals with leprosy . Interestingly, the level of LILRA2 manifestation is definitely significantly higher in individuals with lepromatous leprosy, a disease characterized by Th2 biased immune response leading to severe swelling but poor bacterial killing as Alcaftadine compared to tuberculoid leprosy, which is definitely characterized by Th1 biased response with minimal inflammation but efficient bacterial killing . This suggests that LILRA2 might be an immune modulator that may favor Th2 immune response rather than acting as a simple activating receptor. Moreover, LILRA2 has been shown to inhibit dendritic cell differentiation and reduce antigen demonstration to T cells (a gift from Prof. Hazel Mitchell, University or college of New South Wales, Australia) were labeled with pHrodo phagocytosis particle labeling kit according to the manufacturer’s teaching (Molecular Probes, Eugene, OR). Labeled bacteria Alcaftadine were lyophilized at 5 mg aliquots (2109 particles) and stored at ?80C until use. For subsequent experiments, an aliquot Alcaftadine of the labeled was thoroughly re-suspended in 1 ml of Buffer B (Molecular Probes) and incubated on snow for 10 min. Half (0.5 ml) of the bacteria was pelleted by centrifugation at 500 g for 5 minutes, then opsonized with 0.5 ml of pooled human serum from 5 healthy donors for 30 min on ice  and the other half was remaining in Buffer B (non-opsonized). Opsonized and non-opsonized were added onto.