SOLUBLE PLASMA ANTIGEN IN EXPERIMENTAL SALMONELLA-TYPHIMURIUM INFECTION IN MICE

To detect and characterize Salmonella antigen in blood, outbred CF-1 f emale mice were inoculated intraperitoneally with S. typhimurium LT-2 and blood was assayed by ELISA for Salmonella common structural antige n. Plasma antigen was detectable early in the course of infection and increased in quantity later in the course of illness when animals show ed high grade bacteremia and high counts of splenic bacteria. Antigen was associated with a cell-free plasma fraction of blood, passed throu gh filters with cut-offs of 0.2 mu and molecular mass of 1000 kDa, and was enhanced in detectability after heating to 100 degrees C for 15 m in. Antigen was concentrated by diluting plasma 1:4 in 0.1 M EDTA, hea ting to 100 degrees C, and concentrating the supernate with an ultrafi ltration membrane with a molecular mass cut-off of 15 kDa. By gel filt ration, antigen was associated with a peak at about molecular mass 300 kDa in heated plasma and a peak at about 380 kDa in unheated plasma. These results indicate that murine typhoid infection results in circul ating soluble plasma antigen, which is heat-stable with a molecular ma ss of approximately 300 kDa.