Intracellular signals triggered during association of Mycobacterium lepraeand Mycobacterium bovis BCG with human monocytes

To gain a better understanding of mycobacteria-host cell interaction, the p resent study compared the signal transduction events triggered during the i nteraction of Mycobacterium leprae (the causative agent of leprosy) and of Mycobacterium bovis BCG (an attenuated strain used as a vaccine against lep rosy and tuberculosis) with human monocytes. The assays consisted of pretre ating or not THP-1 cells (a human monocytic cell line) with different kinas e inhibitors, followed by incubation with fluorescein-labelled bacteria and analysis of bacterial association via fluorescence microscopy. The specifi c tyrosine kinase (TK) inhibitor tyrphostin AG126 provided the highest rate s of association inhibition (> 90% for BCG and > 65% for M. leprae). The ea rly activation of TKs during mycobacteria-host cell interaction was confirm ed by immunoblot analysis, demonstrating that in several host cell proteins mycobacteria stimulated tyrosine phosphorylation. The use of the drugs wor tmannin and bisindolylmaleimide I which, respectively, inhibit phosphatidyl inositide 3-kinase (PI 3-kinase) and protein kinase C (PKC), produced lower but consistent results within a 35-60% association inhibition range for bo th bacteria. Dose response curves with these inhibitors were obtained. Simi lar results were obtained when primary human monocytes were used as host ce lls, strongly suggesting that TK, PKC and PI 3-kinase signals are activated during the interaction of human monocytes with both pathogenic and attenua ted species of mycobacteria. (C) 2001 Academic Press.