Fig. 8. Model for CEACAM3 signalling leading to internalization of Neisseria. Following cell contact, CEACAM3-binding Opa variants recruit receptor molecules to the site of adherence. The four CEACAM3-binding Opa variants of the N.gonorrhoeae strain MS11 are shown as an example. Receptor ligation results in phosphorylation of tyrosine residues in the cytoplasmic ITAM motif of the receptor through kinases of the Src family. In granulocytes, Syk kinase may have a key function through its ability to interact specifically with phosphorylated ITAM motifs. However, in epithelial cells that lack Syk, this kinase is not essential. Downstream of receptor activation, the small GTPases Rac and Cdc42 regulate phagocytosis by initiating F-actin assembly, presumably through their downstream effectors such as WASP and the Arp2/3 complex.