Role of macrophage phospholipase D in natural and CpG-induced antimycobacterial activity

Abstract

SummaryThe present study addresses the differential ability of macrophages to control intracellular growth of nonpathogenic Mycobacterium smegmatis (Msm) and pathogenic M. tuberculosis (MTB). Results reported herein show that 3 h post infection, intracellular Msm , but not MTB, was significantly killed by macrophages. As the role of human macrophage phospholipase D (PLD) in the activation of antimicrobial mechanisms has been documented, we hypothesised the role of such enzyme in antimycobacterial mechanisms. To this aim, macrophage PLD activity was analysed at different times after exposure with either pathogenic MTB or non-pathogenic Msm. Results showed that, starting from 15 min after mycobacterial exposure, MTB did not induce macrophage PLD activity, whereas the environmental non-pathogenic Msm stably increased it. The direct contribution of PLD in intracellular mycobacterial killing was also analysed by inhibiting enzymatic activity with ethanol or calphostin C. Results show that PLD inhibition significantly increases intracellular Msm replication. In order to see whether the innate PLD-mediated antimicrobial mechanisms against MTB are also induced after CpG ODN stimulation, the role of PLD has been analysed in the course of CpG-mediated intracellular MTB killing. CpG DNA increased PLD activity in both uninfected and MTB-infected macrophages, and the inhibition of PLD activity resulted in a significant reduction of CpG-induced MTB killing. Taken together, our data suggest a relationship between host PLD activation and the macrophage ability to control intracellular mycobacterial growth.

Synergistic Activation of Macrophages via CD40 and TLR9 Results in T Cell Independent Antitumor Effects

“…Class B CpGs are potent activators of both murine and human mononuclear phagocytes, and M in particular (30,33,34,44). Although CpG and LPS share many immunostimulatory properties, CpG seems to be less toxic in vivo due to stimulation of mononuclear phagocytes in a much more restricted manner (33,34).…”

Janus-faced liposomes enhance antimicrobial innate immune response in Mycobacterium tuberculosis infection

“…Results show that the antimycobacterial activity increased by ABL/PA was mediated by phagolysosome maturation and acidification because the addition of chloroquine or NH 4 Cl upon ABL/PA treatment significantly reduced intracellular mycobacterial killing, particularly after 5 d of MTB infection (Fig. S6B).…”

“…To assess the role of ABL/PA-induced phagolysosome maturation and ROS production in intracellular mycobacterial killing, dTHP-1 cells were infected with MTB, stimulated with liposomes, and then exposed to the lysosomotropic agents chloroquine and NH 4 Cl, which both increase intralysosomal pH and are considered to be general lysosomal inhibitors. Results show that the antimycobacterial activity increased by ABL/PA was mediated by phagolysosome maturation and acidification because the addition of chloroquine or NH 4 Cl upon ABL/PA treatment significantly reduced intracellular mycobacterial killing, particularly after 5 d of MTB infection (Fig.…”

“…In particular, phospholipase D (PLD) activation is necessary for intracellular killing of pathogens induced by natural ligands, such as ATP (2,3), and by microbial ligands, such as CpG oligodeoxynucleotides (4). Interestingly, Mycobacterium tuberculosis (MTB), unlike the nonpathogenic Mycobacterium smegmatis, inhibits PLD activation during phagocytosis, a process that is associated with intracellular survival of the pathogen (4). PLD catalyzes the hydrolysis of the membrane phospholipid, phosphatidylcholine, to generate the metabolically active phosphatidic acid (PA).…”

Host-Directed Therapeutics for Tuberculosis: Can We Harness the Host?

“…HDT targets described in the text are marked in boxes with red shading. (70)(71)(72)(73). Strategies that activate PLD might be desirable as a host therapeutic, but the precise role of this molecule in host defense against M. tuberculosis needs to be better understood.…”