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Interaction of Mycobacterium tuberculosis with human respiratory epithelial cells (HEp-2).

SETTING
Mycobacterium tuberculosis (MTB) is known to adhere to, invade, multiply inside, and modulate respiratory epithelial cell functions. However, the mode and the molecules involved in the interaction of MTB with respiratory cells are not known.


OBJECTIVE
To study post-adherence morphological changes in human respiratory epithelial cells and identify MTB components involved in the binding to these cells.


DESIGN
The mechanism of interaction of MTB human respiratory epithelial cells (HEp-2) was investigated by incubating MTB with HEp-2 cells, whereupon the morphological changes were examined under scanning electron microscopy. MTB components involved in the interaction with HEp-2 cells were identified by probing Western blots of mycobacterial sonicates with biotinylated HEp-2 extracts.


RESULTS
MTB readily bound to the surface of HEp-2 cells. Adherence of tubercle bacilli on the surface caused membrane perturbation resulting in increased surface membrane projections, particularly towards the margins of the cells. Long thin epithelial membrane projections formed loops around the bacilli holding them on the surface. Membrane projections fused to form a web in which the bacilli were entrapped. Concomitant membrane cavitations seen beneath the site of attachment of the bacilli conceivably caused internalization of the organisms. At least five MTB proteins ( approximately 112, 35, 28, 21 and 15 kDa) specific for HEp-2 cells were identified. Of these, the 28 kDa protein was the predominant HEp-2-binding protein and was found to be heparin-binding hemagglutinin (HBHA). While M. bovis BCG strain showed the same five HEp-2-binding proteins, M. smegmatis, displayed only one (31 kDa) HEp-2-specific protein.


CONCLUSION
MTB binds to HEp-2 cells through multiple proteins, and the binding causes membrane perturbations that result in internalization of the organisms.