Improved detection by immunodiffusion of type-specific influenza antibody in avian sera

Various solvents and kinds of agar and agarose as well as various ribonucleoprotein (RNP) antigen preparations were tested in a search for optimal conditions for the detection of low levels of type-specific influenza antibody in avian sera by gel double diffusion. The best results were obtained with one kind of agarose in a solvent with lowered ionic strength (approx. 0.075 M). A hypertonic solvent usually gave worse or negative results, with the exception of one kind of agarose. In general, agarose yielded better results than agar. The results of immuno-precipitation were affected by the strain of influenza virus used for the preparation of RNP antigen.