3B) and recovered a population of F4/80+ macrophages. Interestingly, Itgb2−/− see more macrophages showed a broader range of F4/80 expression than WT macrophages (Supporting Information Fig. 3B). We assessed inflammatory cytokine production in these thioglycollate-elicited macrophages by intracellular

cytokine staining. F4/80high Itgb2−/− peritoneal macrophages exhibited increased TLR4 responses over WT cells (Fig. 2A and B). The percentage of IL-12 p40- and IL-6-producing Itgb2−/− peritoneal macrophages was significantly elevated over WT cells following LPS stimulation, whereas TNF production remained unaffected by β2 integrin deletion, mirroring the phenotype of BM-derived macrophages (Fig. 2B). Thus, these data demonstrate that, in addition to BM-derived macrophages, β2 integrins also negatively regulate TLR-induced IL-12 p40 and IL-6 production in inflammatory macrophage populations. To identify the contribution of β2 integrins to inhibiting TLR responses in vivo, we injected WT and Itgb2−/− mice with LPS i.p. and measured inflammatory cytokine levels in serum up PLX3397 to 4 h after injection. The kinetics for TNF,

IL-12 p40, and IL-6 induction were similar between WT and Itgb2−/− mice, with the peak serum concentration of each cytokine occurring at the same time in both (Fig. 2C). However, differences in the magnitude of cytokine production were observed. Serum IL-12 p40 levels were dramatically increased in Itgb2−/− mice such that by 4 h post-injection, Itgb2−/− animals displayed approximately three times the concentrations observed in WT controls. Itgb2−/− mice also presented with significantly

elevated serum IL-6 and TNF in response to LPS injection (Fig. 2C). While Itgb2−/− mice have changes in leukocyte populations, including increased fantofarone circulating neutrophils, that make interpreting in vivo findings challenging, these data did support our in vitro findings that β2 integrins inhibited TLR responses in two distinct macrophage populations, BM-derived macrophages and thioglycollate-elicited macrophages. TLR stimulation in macrophages results in secretion of the anti-inflammatory cytokine IL-10 that acts in an autocrine or paracrine manner to dampen TLR activation [25]. Interestingly, culture of human macrophages on fibrinogen-coated plates induces IL-10 expression, as well as the expression of proteins such as A20, Hes-1, and ABIN-3, which are known to inhibit TLR signaling [20]. Fibrinogen is a β2 integrin ligand and plating of human macrophages onto fibrinogen-coated plates presumably induces a β2 integrin signal, though other receptors may also be engaged [26-29].