FOWL ANTIBODY. VII. THE EFFECT OF NORMAL FOWL SERUM FACTORS ON SPECIFIC PRECIPITATION AND ON HAEMOLYSIS BY FOWL COMPLEMENT.

The increased precipitation of fowl antibody with antigen in the presence of normal fresh fowl serum (NFS) is due to one or more normal serum factors, including a macroglobulin, which resist heating at 56° for 30 minutes, but are inhibited by EDTA and destroyed at pH values below 5.5. Dialysis against low ionic strength buffers at neutral pH values concentrates the factors in the euglobulin fraction, and with antisera yields antibody-containing pseudoglobulin preparations free of macroglobulin. Enhanced precipitation occurs both in 0.9 and 8 per cent NaCl, but the effect is greater at the lower salt concentration. Its magnitude depends on the antibody preparation, the antigen/antibody ratio and on the concentration (rather than the amount) of the normal serum factors. Its relation to haemolytic complement has been studied but remains obscure.