Cord-forming mycobacteria induce DNA meshwork formation by human peripheral blood mononuclear cells

Abstract Mononuclear phagocytes, that is, monocytes and macrophages, are central in the defense against mycobacteria. Mycobacterium abscessu s is an opportunistic mycobacterial species able to cause chronic pulmonary infections in patients with cystic fibrosis but also soft tissue infections in immunocompetent individuals. Pathogenic isolates of M. abscessus with rough colony morphology form cord-like aggregates. In this study, we investigated the in vitro response of human peripheral blood mononuclear cells (PBMCs) from healthy blood donors to cord-forming M. abscessus strains from cystic fibrosis patients with clinical lung infection. Microscopic examination revealed that the PBMCs produced a coarse fibrous meshwork containing DNA and histones, which surrounded the mycobacterial cords. Thus, the bacterial cord formations were entrapped by monocytes and lymphocytes aggregated onto the DNA-rich meshwork fibers. Mycobacterium abscessus strains with smooth colony morphology, which do not form cords and are readily phagocytosed, did not induce any meshwork formation in PBMCs. The chromatin meshwork may represent a defense mechanism against nondigestible invaders. This study investigates the response of human blood mononuclear cells (PBMCs) to a cord-forming strain of Mycobacterium abscessus. A fibrous chromatin-like meshwork containing DNA and histones is produced by the PBMCs, perhaps as a defense mechanism against other invaders. Overall very nicely done and with well-illustrated results.