Characterization of two monoclonal antibodies directed against serovar A Haemophilus paragallinarum

Two monoclonal antibodies (MAbs) raised against a serovar A Haemophilus paragallinarum were evaluated for their ability to react with 11 reference strains that represented all the recognized serovars and with 27 field isolates of Page serovar A collected from around the world. The MAbs were used in a hemagglutination-inhibition assay. Both MAbs recognized type strains of Page serovar A and Kume serovars A-1 and A-2 but not the type strains of Kume serovars A-3 and A-4. Neither MAb recognized the type strains of Page serovars B and C or Kume serovars B-1, C-1, C-2, C-3, or C-4. When evaluated with the 27 Page serovar A field isolates, both MAbs recognized only 10 isolates. All of the recognized isolates belonged to Kume serovars A-1 (nine isolates) or A-2 (one isolate). All of the field isolates that were not recognized by one or the other of the MAbs either were Kume serovar A-4 (seven isolates) or could not be placed in an existing Kume A serovar (10 isolates). The results indicate that the epitope recognized by these MAbs is present only in strains of H. paragallinarum that belong to Kume serovars A-1 and A-2.