A Sensitive, Single-Radial Diffusion Autoradiographic Zone Size Enhancement Technique for the Assay of Influenza Haemagglutinin

A novel radial-diffusion technique in agarose gels is described which is applicable to the assay of small concentrations of influenza haemagglutinin (HA) antigen. The method is based on single-radial diffusion zone size enhancement (ZE) using autoradiography to demonstrate antigen--antibody reactions. The ZE technique is capable of reliably assaying concentrations of haemagglutinin as low as 0.1 microgram/ml, which represents a 20- to 40-fold increase in sensitivity over conventional single-radial-diffusion techniques. The ZE response is dependent upon the antigenic identity of the 125I-labelled 'marker' HA and the HA antigen being assayed. Haemagglutinins showing variation within a subtype (e.g. H3) show reduced ZE responses and thus the method has potential value for distinguishing between closely related HA antigens.