Tracheal cytotoxin (TCT) is a bacterial virulence factor in whooping cough (and other infections) that triggers leukocyte infiltration and strips airways of ciliated epithelium. However, not all host-bacterial encounters are negative. In the relationship between the glow-in-the dark squid Euprymna scolopes and its luminescent bacterial symbiont Vibrio fischeri, Koropatnick et al. have discovered that the same toxin plays a benign role. In this association, TCT still initiates apoptosis of ciliated cells and host cell infiltration. However, these cellular responses are triggered when juvenile squid first encounter V. fischeri and constitute a normal developmental stage in the generation of the specialized light organ that allows it to accommodate the incoming symbiont.
T. A. Koropatnick, J. T. Engle, M. A. Apicella, E. V. Stabb, W. E. Goldman, M. J. McFall-Ngai, Microbial factor-mediated development in a host-bacterial mutualism. Science 306, 1186-1188 (2004). [Abstract] [Full Text]