Nevertheless, this fine-tuning of NF-κB activation by β2 integrins contributed to dramatic differences in the ability of macrophages to respond to TLRs and induce NF-κB-dependent gene expression. Importantly, we noted that the affected genes encompassed both “primary response” (Tnf, Cxcl1, Cxcl2) and “secondary response” (Il12B, Il6) genes that encode for inflammatory cytokines, chemokines, and anti-apoptotic functions Sotrastaurin [38]. We also observed a direct effect

of β2 integrin deletion on enhancing p65/RelA binding to the Il12b (IL-12 p40) promoter downstream of LPS stimulation. However, it should be noted that fine-tuning of the NF-κB pathway by β2 integrins did not control expression of all “NF-κB-dependent” genes tested. Peculiar omissions from this list include A20 and iNOS, which were both expressed similarly between WT and Itgb2−/−

macrophages, suggesting that other pathways may be influenced by β2 integrin signals to control transcription of these genes. One such pathway is p38 MAPK signaling. Itgb2−/− macrophages demonstrated a reduced ability to phosphorylate, and therefore activate, p38 following LPS treatment, consistent with the fact that selleck chemicals β2 integrin outside-in signals are known to directly activate the MAPK pathway [14]. In addition to its well-regarded proinflammatory activities [39], activation of p38 and its subordinate protein kinases MSK1 and MSK2 has been implicated in dampening inflammation through several mechanisms. For example, p38 activity limits Th1 responses

to Leishmania by destabilizing IL-12 p40, though not TNF, mRNA stability [32]. p38 and MSK1/2-derived signals have also been shown to negatively regulate TLR responses by inhibiting inflammatory cytokine transcription directly or by promoting IL-10 synthesis through activation of CREB and Atf-1 transcription factors [30-32]. In addition to IL-10, p38-directed A20 and ABIN-3 production has previously been linked to TLR suppression by β2 integrins [20]. However, Itgb2−/− macrophage TLR hypersensitivity could not be attributed to deficiencies in A20, ABIN-3, Hes-1 or to changes in IL-10 production or signaling, arguing against a role for these proteins in β2 integrin-medited TLR suppression. Interestingly, Itgb2−/− macrophages presented with higher TLR-induced Niclosamide levels of some of these inhibitors than WT cells, likely owing to enhanced NF-κB activation. The differences between our results and those of Wang et al. [20] may be due to our use of plastic petri dishes to induce β2 integrin signals instead of plate-bound fibrinogen, which itself is known to bind to additional receptors [26-29]. Indeed, fibrinogen’s ability to dampen TLR activity in macrophages may be at least partially β2 integrin-independent as we found that inflammatory cytokine secretion was suppressed in Itgb2−/− macrophages similar to WT cells after plating onto fibrinogen-coated plates (data not shown).