In vitro and in vivo macrophage function can occur independently of SLP-76

Expression of SH2 domain-containing leukocyte-specific phosphoprotein of 76 kDa (SLP-76), a hematopoietic cell-specific adapter protein, is required to couple Syk family tyrosine kinase activation to downstream mediators such as phospholipase C (PLC)-γ following TCR, platelet collagen receptor and mast cell FceR stimulation. In addition to T cells, mast cells and platelets, SLP-76 is expressed in monocytes and macrophages. To determine the role of SLP-76 in FcγRstimulated signaling pathways in macrophages, we examined cultured bone marrow-derived macrophages (BMM) from SLP-76 ‐/‐ and wild-type mice. In this study, we show that FcγR crosslinking rapidly induces tyrosine phosphorylation of SLP-76 in wild-type BMM. Surprisingly, however, BMM from SLP-76 ‐/‐ mice activate ERK2 and phosphorylate PLC-γ2 following FcγR ligation. Furthermore, SLP-76 ‐/‐ BMM display normal FcγR-dependent phagocytic function and reactive oxygen intermediate production. SLP-76 ‐/‐ and SLP-76 / BMM secrete comparable levels of IL-12 in response to lipopolysaccharide and IFN-γ. To examine macrophage function in vivo, SLP-76 ‐/‐ mice were challenged i.v. with Listeria monocytogenes. SLP-76 ‐/‐ mice survive and efficiently contain the acute phase of infection similar to wild-type mice but exhibit a stable chronic infection attributed to the lack of mature T cells. These data show that, although SLP-76 is required to couple Syk family PTK activity to downstream mediators and effector functions in FcγR-induced pathways in some cell types, activation of FcγR-dependent pathways occurs independently of SLP-76 in BMM.