This “outside-in” signaling pathway requires ITAM signals from DAP12 and FcRγ, and also involves early effectors such as the Src family kinases and Syk in neutrophils and macrophages [14, 15]. Because β2 integrins signal through
ITAM adapters in myeloid cells, we hypothesized that β2 integrin signaling may also inhibit TLR responses. There have been conflicting reports in the literature regarding the influence of β2 integrin signaling on TLRs, with some studies demonstrating that β2 integrins can promote TLR-induced inflammation [16-18], whereas others have reported negative roles for these integrins in TLR responses [19, 20]. Therefore, the nature in which β2 integrins interface with TLR activation and cytokine secretion is complex selleck compound and unclear.
To better define the contribution of β2 integrins to regulation of TLR signaling, we have examined inflammatory responses in the absence of all β2 integrins. Here we demonstrate that deletion of all β2 integrins rendered myeloid cells hypersensitive to TLR stimulation in vitro and in vivo, showing an inhibitory role for β2 integrins in TLR responses. Furthermore, https://www.selleckchem.com/products/ink128.html we examined potential direct and indirect mechanisms by which β2 integrins caused this inhibition, and found that β2 integrins have a direct effect on IκBα degradation that was pronounced in β2 integrin-deficient cells through both early and late phases of TLR stimulation, thus implicating β2 integrin signals in inhibiting NF-κB pathway activation to calibrate inflammatory responses. The four β2 integrins, LFA-1 (lymphocyte function-associated antigen 1, αLβ2), Mac-1 (macrophage-1 antigen, αMβ2), CR4 (αXβ2), and CD11d-CD18 (αDβ2) are heterodimers that consist of distinct CD11 alpha subunits in association with the common
beta chain, CD18 (β2), which is encoded by the Itgb2 gene . To examine whether β2 integrin signaling regulates TLR responses, we compared the cytokine secretion profiles of bone marrow-derived (BM-derived) macrophages from wild-type Erastin cell line (WT) and Itgb2−/− mice, which are deficient in CD18 and thus are unable to express any of the β2 integrins on the cell surface (Supporting Information Fig. 1A) . Despite the inability of Itgb2−/− BM-derived macrophages to express Mac-1, these cells exhibited surface F4/80 expression and upregulated MHC II in response to IFN-γ treatment (Supporting Information Fig. 1A and B), demonstrating that they were bona fide macrophages. Furthermore, β2 integrin-deficient macrophages exhibited similar or slightly lower levels of cell surface TLR2, TLR4, and Dectin-1 protein and TLR9 mRNA (Supporting Information Fig. 1C and D). To determine how β2 integrin signals influence TLR activity, we stimulated Itgb2−/− BM-derived macrophages with a panel of TLR agonists, including LPS (TLR4), CpG B DNA (TLR9), and zymosan (TLR2).