ANTIGENS IN IMMUNITY

Abstract

SummaryAn investigation of the immunogenicity of three flagellar preparations, namely, intact flagella, polymerized flagellin and the soluble, low molecular weight protein flagellin, was performed in rats. Despite the similarity of in vitro serological behaviour of these three antigens, important differences in their in vivo immunological effectiveness were noted. While flagella and polymerized flagellin caused first 19S antibody formation and later prolonged 7S antibody formation, flagellin appeared to be quite incapable of inducing a 19S primary response. Further, the peak titres achieved with Hagellin were lower than those with the other antigens. Polymerized flagellin was somewhat less immunogenic than were flageila.The study covered a dosage range of 10 logs.10, i.e., from 10–12 g. to 10–2 g. Clear‐cut dose‐response relationships could be observed for the shortlived 19S response caused by flagella or polymerized flagellin, over the dose range 10 ng. (0·01 μg.) to 10 μg. For the 7S response, particularly with flagellin, dose‐response relationships were not established. Remarkably small doses, namely, 100 ng. (0·1 μg.) of flagella, 1 μg. of polymerized flagellin and 10 μg. (0·01 μg.) of flagellin caused peak 7S titres to appear. Doses as small as 100 pg. (0·0001 μg.) occasionally caused antibody production.Doses of antigen too small to cause a detectable 19S response were followed by a lag period of about two weeks during which serum antibody levels remained below the threshold of our test. Then antibody litres rose steadily until six or eight weeks after injection, Peak levels were maintained for over six weeks, and fell slowly. At 34 weeks, when the experiments were stopped, antibody litres were still quite high, The lag period with doses which caused 19S antibody production was much shorter, generally less than four days. In such animals, 19S antibody was gradually replaced by 7S antibody during the second week, and again it took several weeks for peak 7S litres to be leached.These results emphasized the need to use small doses in any meaningful study of antigen distribution, localization, behaviour and fate.