Immunospecific T-lymphocyte stimulation by membrane proteins from Francisella tularensis

Membranes from a capsule-deficient mutant of the live-vaccine strain of Francisella tularensis (F. tularensis LVS) were treated with N-lauroyl sarcosinate (Sarkosyl; CIBA-GEIGY Corp., Summit, N.J.). When the Sarkosyl-insoluble fraction was heated in the presence of sodium dodecyl sulfate and mercaptoethanol and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, several polypeptides were distinguished. Four major polypeptides were eluted from the gel, each of which stimulated lymphocytes from tularemia-vaccinated individuals but not from nonvaccinated individuals. The stimulation occurred mainly in T lymphocytes. Radioactive labeling of surface proteins of the capsule-deficient bacteria indicated that at least two of the four polypeptides originated from outer membrane proteins. The results suggest that several membrane proteins of F. tularensis LVS induce a specific T-lymphocyte response.