The significance of the bursa of Fabricius in relation to the synthesis of 7S and 19S immune globulins and specific antibody activity in the fowl.

Fowls in which the development of the bursa of Fabricius was suppressed, by the injection of testosterone , failed to develop normal serum levels of both 7S and 19S immune globulins. In some instances the 7S immune globulin, in the serum of bursaless fowls, suggested the survival of clones of cells synthesizing 7S immune globulin with a sharply defined electrophoretic mobility. Thus the bursa may make some fundamental contribution to immunological competence and when this effect is markedly reduced by testosterone treatment the few cells which are capable of globulin synthesis subsequently proliferate and produce globulin lacking the usual electrophoretic heterogeneity of mobility. The indirect haemagglutination test showed that normal fowls developed 7S and 19S antibodies 7 days after the injection of BSA. At this time most of the activity was in the 19S fraction. However, 35 days after the primary injection and 7 days after a second stimulus, highest activity was in the 7S fraction. Precipitin activity was shown at 7 and 35 days in the 7S but not the 19S fractions. The 19S but not the 7S immune globulins were sensitive to mercaptoethanol. Bursaless fowls, when given similar BSA injections, failed to show any antibody activity in their sera and the antigen was circulating 7 days later, when normal fowls had developed antibody. When time was given for antigen clearance, bursaless fowls still failed to respond to a secondary BSA stimulus. Surgical bursectomy at hatching reduced, but did not eliminate, specific antibody production. Although there was a significant decrease in thymus weight in testosterone treated fowls, this was not observed in surgically bursectomized fowls. Nevertheless, in both these groups of fowls there was a significant decrease in secondary lymphoid foci in the spleen and in spleen weights. Thus, secondary lymphoid foci appeared to be more dependent on the bursa than on the thymus. The significance of the synthesis of 7S immune globulin, which occasionally has a sharply defined electrophoretic mobility, by bursaless fowls together with their inability to show any specific antibody activity, is discussed in relation to the function of the bursa.