Activation of lobster hemocytes for phagocytosis

Activation of lobster (Homarus americanus) hemocytes for phagocytosis of sheep erythrocytes (SRBC) was demonstrated in vitro by incubation with lipopolysaccharide and by prolonged adherence to glass coverslips. Morphological changes, which preceded phagocytic activation, were detected by phase microscopy and Nomarski interference microscopy. These included spreading, the formation of filopodia and pseudopodia, granular darkening and dispersion, and vacuolation. Hemolymph serum opsonin greatly enhanced the recognition and phagocytosis of SRBC by activated hemocytes. Increases of 15 to 20 times background levels were observed both in the proportion of hemocytes which were actively phagocytic, and the percent of rosette-forming hemocytes. This suggested that the enhanced phagocytosis was the result of both the recruitment of a quiescent precursor population during activation, and an increase in the availability of opsonin binding sites on hemocyte membranes.