Institut de Biologie Moleculaire et Cellulaire, CNRS UPR 9022, 15 rue Rene Descartes, Universite Louis Pasteur, 67084 Strasbourg Cedex, France.
Unite de Pathogenie Bacterienne des Muqueuses, Institut Pasteur, 25 rue du Dr. Roux 75724 Paris Cedex 15, France.
The activation of an immune response requires recognition of microorganisms by host receptors. In drosophila, detection of Gram-positive bacteria is mediated by cooperation between the peptidoglycan-recognition protein-SA (PGRP-SA) and Gram-negative binding protein 1 (GNBP1) proteins. Here we show that some Gram-positive bacterial species activate an immune response in a PGRP-SA- and GNBP1-independent manner, indicating that alternative receptors exist. Consistent with this, we noted that PGRP-SD mutants were susceptible to some Gram-positive bacteria and that a loss-of-function mutation in PGRP-SD severely exacerbated the PGRP-SA and GNBP1 mutant phenotypes. These data indicate that PGRP-SD can function as a receptor for Gram-positive bacteria and shows partial redundancy with the PGRP-SA-GNBP1 complex.