The Tyrosine Kinase Btk Regulates the Macrophage Response to Listeria monocytogenes Infection

In this study we investigated the role of Bruton's tyrosine kinase (Btk) in the immune response to the Gram-positive intracellular bacterium Listeria monocytogenes (Lm). In response to Lm infection, Btk was activated in bone marrow-derived macrophages (BMMs) and Btk−/− BMMs showed enhanced TNF-α, IL-6 and IL-12p40 secretion, while type I interferons were produced at levels similar to wild-type (wt) BMMs. Although Btk-deficient BMMs displayed reduced phagocytosis of E. coli fragments, there was no difference between wt and Btk−/− BMMs in the uptake of Lm upon infection. Moreover, there was no difference in the response to heat-killed Lm between wt and Btk−/− BMMs, suggesting a role for Btk in signaling pathways that are induced by intracellular Lm. Finally, Btk−/− mice displayed enhanced resistance and an increased mean survival time upon Lm infection in comparison to wt mice. This correlated with elevated IFN-γ and IL-12p70 serum levels in Btk−/− mice at day 1 after infection. Taken together, our data suggest an important regulatory role for Btk in macrophages during Lm infection.