In innate immunity, pathogen associated molecular patterns (PAMPs) are recognized by pattern recognition receptors (PRRs) that activate signaling cascades and effector mechanisms, like phagocytosis which act to clear the microbes out of the host's system. We are interested in the phagocytosis of bacteria in Drosophila because not much is know about cellular immunity in flies and it may be the first-line immune response. In a pilot genetic screen, we have identified 8 mutations that affect the phagocytosis of E. coli (a Gram- bacteria) and/or S. aureus (a Gram+ bacteria) in vivo. The specific aims of this proposal are: 1. To elucidate the role two catalytic peptidoglycan recognition proteins (PGRP-SC1a/b and PGRP-SC2) play in the phagocytosis of bacteria and the activation of the antimicrobial peptide (AMP) response. Two of our phagocytosis mutations affect PGRP-SC1a/b and PGRP-SC2 expression. We will examine how these mutants affect phagocytosis and AMP responses. 2. To determine if disruption of the outer membrane of Gram-negative bacteria is necessary for recognition and clearance of the bacteria by the Drosophila immune response. We believe that this may be occuring to allow access to peptidoglycan in the cell wall which can trigger the downstream AMP responses. 3. To examine how genes important for immune responses or phagocytosis affect phagosome maturation in vivo. We have preliminary data indicating that PGRP-SC2, Rab14 and AMPs may be important for phagosome maturation. With these experiments, we hope to understand the role these genes play in recognition and phagocytosis of bacteria in vivo.