Macrophages recognise and respond to molecular markers of danger through Toll-like receptors (TLRs) that signal by recruiting Toll/interleukin 1 receptor-like (TIR) domain-containing adaptor proteins. Slp65/76 and CSK interacting membrane protein (Scimp), a member of the palmitoylated transmembrane adaptor protein family, was recently shown to act as a novel non-TIR TLR adaptor protein in murine macrophages, facilitating Tlr4 tyrosine phosphorylation and selectively promoting the production of the pro-inflammatory cytokines Il-6 and Il-12p40. Here, I reveal that a downstream translational start site in Scimp mRNA generates an alternative translational variant, Scimp TV1, lacking the first 13 amino acids which encode the extracellular region. We found that macrophages generate two distinct Scimp variants through the process of leaky ribosomal scanning. Scimp TV1 was retained intracellularly, whereas full-length Scimp localised to macrophage filopodia. A CRISPR-generated mouse line that selectively expresses Scimp TV1 but not full-length Scimp (Scimp TV1 mice) was used to elucidate Scimp functions in myeloid cells. In CSF-1-derived macrophages from Scimp TV1 mice, Il-12p40 production following chronic LPS exposure was impaired. Furthermore, in GM-CSF-derived macrophages that express high levels of Scimp, CpG DNA-inducible production of Il-6, Il-12p40 and Tnf was enhanced in cells from Scimp TV1 mice. These data suggest that intracellularly localised Scimp TV1 selectively promotes responses downstream of the endosomal TLR, Tlr9. Investigating Scimp-dependent Tlr4 tyrosine phosphorylation, Y749 phosphorylation was shown to be required for maintenance of total Tlr4 protein levels and signalling, whereas Y672 phosphorylation exerts its proinflammatory effects through the promotion of Erk1/2 phosphorylation. Furthermore, Scimp facilitates Tlr4 Y672 phosphorylation to permit downstream inflammatory responses, with the Syk tyrosine kinase likely phosphorylating Y672 on Tlr4. Collectively, the findings reveal new insights into TLR-mediated activation of innate immune cells by the processes of alternative translation and tyrosine phosphorylation on TLRs.