Phagocytosis is responsible for the elimination of particles of widely disparate sizes, from large fungi or effete cells to small bacteria. 

Though superficially similar, the molecular mechanisms involved differ: engulfment of large targets requires phosphoinositide 3-kinase (PI3K), while that of small ones does not.

Researchers report in the journal Nature Communications that inactivation of Rac and Cdc42 at phagocytic cups is essential to complete internalization of large particles.

Authors identified the RhoGAPs family members responsible for GTPase inactivation. Silencing these GAPs impairs phagocytosis of large targets.

The GAPs are recruited to large—but not small—phagocytic cups by products of PI3K, where they synergistically inactivate Rac and Cdc42.

Remarkably, the prominent accumulation of phosphatidylinositol 3,4,5-trisphosphate characteristic of large-phagosome formation is less evident during phagocytosis of small targets, accounting for the contrasting RhoGAP distribution and the differential requirement for PI3K during phagocytosis of dissimilarly sized particles.

http://www.nature.com/ncomms/2015/151014/ncomms9623/full/ncomms9623.html