Concanavalin A and the in vitro induction in macrophages of vacuolation and lysosomal enzyme synthesis

Concanavalin A (ConA) induced extensive vacuolation in mouse peritoneal macrophages. Electron microscopic observations on thin sections reveal that the vacuoles are essentially empty except for minute vesicles attached to their inner periphery. The vacuoles consist of irregular structures and are heterogeneous in size distribution. ConA-induced vacuoles exhibit high acid phosphatase activity, suggesting fusion between vacuoles and lysosomes. Induction of acid phosphatase in ConA-treated macrophages was studied under several cultivation conditions. ConA-treated macrophage cultures responded in increase in acid phosphatase activity early after exposure to the lectin, a significant increase recorded already after 1 h. When cultivated in 1% serum medium for 48 h, ConA-treated macrophages exhibit twice the activity of acid phosphatase at zero time as well as that of non-treated control cultures. The effect of ConA on thioglycolate-stimulated mouse peritoneal macrophages was also studied. Vacuole formation resulting from lectin binding and internalization is discussed in terms of possible lectin effects on membrane fluidity, fusion capacity, surface to volume conservation during vacuole formation, fusion of vacuoles with lysosomes and intravacuolar lysosomal enzyme activities. The phenomenon of lysosomal enzyme induction as a result of ConA treatment is being correlated with enzyme induction due to other stimuli.