Mast cell cytonemes as a defense mechanism against Coxiella burnetii

Mast cells (MCs) are critical mediators of inflammation; however, their microbicidal activity against invading pathogens remains largely unknown. Here, we describe a nonpreviously reported antibacterial mechanism used by MCs against Coxiella burnetii, the agent of Q fever. We show that C. burnetii interaction with MCs does not result in bacterial uptake but rather induces the formation of extracellular actin filaments named cytonemes. MC cytonemes express cathelicidin and neutrophil elastase and mediate the capture and destruction of entrapped bacteria. We provide evidence that MC cytoneme formation and microbicidal activity are dependent on the cooperation of the scavenger receptor CD36 and Toll-like receptor 4. Taken together, our results suggest that MCs use an extracellular sophisticated mechanism of defense to eliminate intracellular pathogens, such as C. burnetii, before their entry into host cells. The human mast cell line HMC-1.2 was cultured in Iscove's Modified Dulbecco's Medium (IMDM, Life Technologies) supplemented with 10% fetal bovine serum (FBS), 100 IU/ml penicillin and 50 µg/ml streptomycin (Life Technologies) at 37°C.