INSECT IMMUNITY - EARLY FATE OF BACTERIA INJECTED IN SATURNIID PUPAE

Saturniid pupae have previously been shown to synthesize a set of antibacterial proteins in response to an injection of viable nonpathogenic bacteria (Boman, H. G., Nilsson-Faye, I., Paul, K., and Rasmuson, T., Jr. 1974. Insect immunity. I. Characteristics of an inducible cell-free antibacterial reaction hemolymph of Samia cynthia pupae; Infec. Immun., 10, 136-145; Faye, I., Pye, A., Rasmuson, T., Boman, H. G., and Boman, I. A. 1975. Insect immunity. II. Simultaneous induction of antibacterial activity and selective synthesis of some hemolymph proteins in diapausing pupae of Hyalophora cecropia and Samia cynthia). Infec. Immun., 12, 1426-1438). It show here that two such injected bacteria, Enterobacter cloacae and Escherichia coli, were rapidly eliminated from the hemolymph. The distribution of the injected bacteria was studied by the use of radioactively labeled E. coli, which were traced by combustion of tissue samples and by radioautography. Both methods showed that the bacteria appeared most frequently in the upper distal ends of the pupae. In the radioautographic study this was expressed as a high number of silver grain-containing cells. These cells appeared singly or as two to five cells clumped together, preferentially attached to the fat body. No decisive effect was shown on either the elimination of bacteria from hemolymph or the appearance in the tissue when pupae were treated with actinomycin D or cycloheximide. Phagocytosis by adhesive hemocytes is discussed as an explanation of bacterial elimination from the hemolymph. © 1978.