Impact of surface receptors TLR2, CR3, and FcγRIII on phagocytosis and intracellular survival in macrophages.

The virulence-associated protein A (VapA) produced by virulent allows it to replicate in macrophages and cause pneumonia in foals. It is unknown how VapA interacts with mammalian cell receptors, but intracellular replication of avirulent lacking can be restored by supplementation with recombinant VapA (rVapA). Our objectives were to determine whether the absence of the surface receptors Toll-like receptor 2 (TLR2), complement receptor 3 (CR3), or Fc gamma receptor III (FcγRIII) impacts phagocytosis and intracellular replication in macrophages, and whether rVapA restoration of virulence in is dependent upon these receptors. Wild-type (WT) murine macrophages with TLR2, CR3, or FcγRIII blocked or knocked out (KO) were infected with virulent or avirulent , with or without rVapA supplementation. Quantitative bacterial culture and immunofluorescence imaging were performed. Phagocytosis of was not affected by blockade or KO of TLR2 or CR3. Intracellular replication of virulent was not affected by TLR2, CR3, or FcγRIII blockade or KO; however, avirulent replicated in TLR2 and CR3 macrophages but not in WT and FcγRIII. rVapA supplementation did not affect avirulent phagocytosis but promoted intracellular replication in WT and all KO cells. By demonstrating that TLR2 and CR3 limit replication of avirulent but not virulent and that VapA-mediated virulence is independent of TLR2, CR3, or FcγRIII, our study provides novel insights into the role of these specific surface receptors in determining the entry and intracellular fate of .