Mycobacterium tuberculosis H37Rv is more effective compared to vaccine strains in modulating neutrophil functions: an in vitro study

Neutrophils are the primary cells contributing to initial defense against mycobacteria. Yet, little is known about the potential of various mycobacterial strains to stimulate neutrophils. This study was focused to compare the differential capacity of vaccine strains, Mycobacterium bovis bacillus CalmetteGuerin (BCG) and Mycobacterium indicus pranii (Mw), and laboratory strain H37Rv to activate and enhance neutrophil functions. The expression of phenotypic markers like Fc? receptor, toll-like receptor (TLR), and chemokine receptor; secretion of pro-inflammatory cytokines; and the rate of apoptosis were studied in infected neutrophils. Increased expression of CD32, CD64, TLR4, and CXCR3; increased TNF-a secretion; and downregulation of early apoptosis were observed in H37Rv-infected neutrophils. Among the vaccine strains, BCG increased the expression of only CD32 on neutrophils, while Mw was comparatively ineffective. To understand the paracrine role of neutrophils, the supernatants from infected neutrophils were used to stimulate monocytes and T helper cells. The secretory molecules from all infected neutrophils increased the expression of CCR5 on monocytes, whereas only H37Rv-infected supernatant increased the expression of CCR7 on monocytes and CD69 on T cells. Thus, H37Rv was more effective in activating neutrophils and in turn stimulating monocytes and T cells. By comparison, vaccine strains were less effective in modulating neutrophil functions.