A correlation between growth rate, apoptosis, and tumor necrosis factor-α in umbilical cord blood cells infected with two strains of Mycobacterium tuberculosis

BACKGROUND: Using umbilical cord blood (UCB) cells, it was demonstrated that three virulent isolates, two highly transmissible clinical isolates and the virulent laboratory strain, demonstrated rapid growth in the UCB cells, which was significantly faster than the growth rate observed for a unique isolate. There was also a significant increase in the amount of tumor necrosis factor (TNF)-alpha elicited from the UCB cells after infection with the unique isolate compared to the hypervirulent isolates. This study investigated whether neutralization or addition of TNF-alpha within this system would alter growth rates and apoptosis. STUDY DESIGN AND METHODS: Ten UCB samples were obtained for these experiments and adherent cells were isolated. Two clinical isolates, one virulent and one unique, were used. Colony-forming units were assessed at 3 hours postinfection (Day 0) and on Day 7 to generate growth ratios. TNF-alpha antibody or exogenous TNF-alpha was added after the 3-hour incubation period. Viability of the UCB cells was assessed. Apoptosis was measured using terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling staining. RESULTS: There was no significant difference in the growth ratio for the virulent strain regardless of the presence of TNF-alpha antibody. There was a significant increase for the nonvirulent strain after the addition of antibody. There was an increase in viability for the UCB cells in the presence of antibody, suggesting a decrease in TNF-alpha-dependent apoptosis. Addition of exogenous TNF-alpha to the UCB cells after infection with the virulent strain decreased the growth ratio with a significant increase in apoptosis. CONCLUSIONS: The TNF-alpha response of the UCB cells is related to the infecting strain and the intracellular growth of the strain of Mycobacterium tuberculosis is not directly controlled by the level of TNF-alpha. This cytokine is at the start of a powerful cascade of transcription factors with numerous pleiotropic effects; consequently abrogating/enhancing a single direct outcome was difficult, with only slight alterations in growth.