Precipitating and agglutinating activity in duck anti-soluble protein immune sera

Ducks were inoculated parenterally, up to 4 times, with bovine serum albumin (BSA), B gamma globulin (BGG), or horse gamma globulin (HGG). Their sera were tested in immunodiffusion tests for precipitins. Only BSA and BGG induced precipitins. Only 7 of 443 sera tested, obtained from 3 of 62 inoculated ducks, developed a precipitin line with homologous antigen. All 7 sera were obtained from the earliest bleeding (7 days) after inoculation. Sera were also tested for agglutinins in direct passive hemagglutination (DPHA) and direct red-cell-linked antigen tests (DRCLAT) and for nonagglutinating antibodies in indirect red-cell-linked antigen tests (IRCLAT). No duck had a passive-hemagglutination-demonstrable primary immune response. Demonstrable DPHA titers after subsequent inoculations were very low compared with responses to these antigens of other species noted by other workers. Duck immune response was greatly diversified: all inoculation regimens that induced agglutinins in some ducks left others completely unstimulated. Precipitins and agglutinins of the same ducks correlated well: those 7 sera that had precipitins also had the highest DPHA titers for the 3 donor ducks. However, hemagglutinating titer and presence of precipitins in sera of different ducks correlated poorly. Increasing the age of the ducks at the first inoculation from 6 to 10 weeks increased the number of responders and DPHA titers of their sera. Non-agglutinating antibodies were demonstrated in anti-BSA sera: in IRCLAT, the sera had titers 2-to-256-fold higher than the sera in DPHA or DRCLAT had. Duck immunoglobulins were deficient in those immunological reactions (precipitation and agglutination) that require functional bivalency.