Insect immunity. 11. Simultaneous induction of antibacterial activity and selection synthesis of some hemolymph proteins in diapausing pupae of Hyalophora cecropia and Samia cynthia

Abstract

Pupae of the giant silkmoth S. cynthia have a humoral antibacterial activity, induced by viable, nonpathogenic gram-negative bacteria (H.G. Boman et al., 1974). This activity is formed simultaneously with a selective incorporation of amino acids into 8 polypeptide chains characterized by their electrophoretic behavior. If actinomycin D or cycloheximide are given early, no antibacterial activity is found. If the inhibitors are given at the time of maximum activity, there is no effect with actinomycin D but a rapid decrease of activity occurs with cycloheximide. The mRNA seems stable, but there is a turnover of at least 1 protein component. Hemolymph from immunized pupae of H. cecropia was fractionated by ammonium sulfate precipitation. This procedure together with isotope distribution after co-electrophoresis in polyacrylamide gels, was used for comparing the response to injury and to different infections. Almost identical polypeptide patterns are obtained as a response to infection with either viable Enterobacter cloacae or Bacillus subtilis. These patterns differ qualitatively and quantitatively from the injury effect created by an injection as such. There is only a low antibacterial activity in each of the 4 fractions obtained by ammonium sulfate precipitation. A combination of 3 fractions restores a high bactericidal activity. Fractionation of hemolymph from untreated pupae provide evidence for at least 1 preexisting factor which stimulates the killing of E. coli. The osmotic pressure of the bacteria contribute to the antibacterial activity towards E. coli, but not towards B. subtilis. Killing of E. coli is inhibited by lipid A and to a lesser extent by an inhibitor of proteolytic enzymes. The similarities and differences with the mammalian complement system are discussed.