Interleukin-1 or tumor necrosis factor-alpha augmented the cytotoxic effect of mycobacteria on human fibroblasts: Application to evaluation of pathogenesis of clinical isolates of Mycobacterium tuberculosis and M-avium complex

Mycobacteria-induced in vitro events reflecting human tuberculosis can cont ribute to the evaluation of the pathogenesis of Mycobacterium tuberculosis (MTB), In this study, we propose such an in vitro method based on live myco bacteria-induced cytotoxicity to human cell lines. When human lung-derived normal fibroblast cell line MRC-5 was infected with various strains of myco bacteria (M, tuberculosis H(37)Rv and H-37 Ra, Mycobacterium avium 427S and 2151SmO, and Mycobacterium bovis BCG Pasteur and Tokyo), the fibroblasts w ere killed by mycobacteria according to the degree of virulence, Other huma n originated macrophage (U-937, THP-1), myeloid (HL-60), and epithelial car cinoma (A549) cell lines exhibited a similar cytotoxic response to virulent mycobacteria, MRC-5 was most susceptible to virulent mycobacteria among va rious human cell lines examined, The cytotoxicity was enhanced by the proin flammatory cytokines, interleukin-1 (IL-1) and tumor necrosis factor-a (TNF -alpha), which in the absence of mycobacteria stimulate the growth of norma l human fibroblasts, This in vitro evaluation system was applied to clinica l isolates of drug-sensitive MTB (DS-MTB), drug-resistant MTB (DR-MTB) incl uding multidrug-resistant (MDR-MTB), and M. avium complex (MAC), MTB strain s (n = 24) exhibited strong cytotoxic activity, but MAC strains (n = 5) had only weak activity, Furthermore, there was no significant difference in cy totoxicity between DS-MTB (n = 11) and DR-MTB (n = 13), Collectively, these results suggest that this new in vitro system is useful for evaluating the pathogenesis of mycobacteria and that there was no difference in the patho genesis between drug-susceptible and drug-resistant clinical isolates.