PI3K is one of the downstream effector of activated SYK. The p85 alpha regulatory subunit of PI3K have been shown to interact with SYK and FCGRs, and transient and restricted accumulation of lipid products of the kinase have been observed at sites of the phagosomal cup (Yanagi et al. 1994, Marshall et al. 2001). Leverrier at al. has demonstrated that p110beta is the major class I catalytic isoform required for FCGR-mediated phagocytosis by primary macrophages (Leverrier at al. 2003). p85 alpha subunit interacts with phosphorylated SYK at tyrosine 317 with its C-terminal SH2 domain, whereas other tyrosine residues like 342 and 346 in the linker region may contribute to the interaction with N-terminal SH2 domain (Moon et al, 2005). The main role of PI3K in phagocytosis appears to be the regulation of pseudopod extension necessary for particle internalization and may also regulate phagocytosis through activation of ERK (Garcia-Garcia & Rosales. 2002).