Human neutrophil chemotactic response to group A streptococci: bacteria-mediated interference with complement-derived...

The influence of M protein on the capacity of group A streptococci to generate neutrophil chemotactic activity in normal human serum was examined. Incubation of serum with M- bacteria for up to 10 min led to the production of chemotactic activity. In contrast, incubation of serum with M+ bacteria did not elicit serum chemotactic activity over a 1-h period, even though complement was activated to completion. Further experiments revealed that both M+ and M- bacteria could inhibit the chemotactic activity of serum preexposed to zymosan. However, the M+ bacteria possessed a 130-fold-greater inhibitory capacity in this regard than the M- bacteria. This antichemotactic property was not detectable in the fluid phase of serum incubated with bacteria, thereby ruling out neutrophil-directed effects. Treatment of the bacteria with trypsin resulted in the release of the inhibitory molecule, suggesting that proteins are involved in its maintenance at the cell surface. However, the resistance of the chemotactic factor inactivator to pepsin and trypsin indicated that the protease-sensitive M protein was not involved. These results demonstrate a heretofore uncharacterized activity of group A streptococci that may contribute to virulence through modulation of the host chemotactic response.