Demonstration of gas vesicles phagocytosis by J774A.1 monolayer cells. Gas vesicle preparations were added to monolayer cells as described, subsequently removed and the monolayers rinsed with fresh media, then maintained in culture. These representative 12 h post treatment micrographs of immunostained samples demonstrate that appropriate antibody detects each of the SIV encoded peptides in numerous cells of the r-GV treated monolayers. Control monolayers - A, received media only. Experimental monolayers received media containing purified gas vesicle preparations expressing Tat - B, Rev - C or Nef1 - D. Original magnification 400×.