Three different antisera against P1 antigen tested with hemagglutination test. Five samples each with the 3 genotypes P¹P¹(▴), P¹P²(Δ), P²P² (•) were tested with 2 monoclonal anti-P1 reagents [Immuclone (MAb1), Seraclone (MAb2)] and a polyclonal (PAb) anti-P1 goat antiserum as indicated on the x-axis. Agglutination reactions were visually graded between 0 and 4+ and registered on the y-axis.