Antigenic structure and relationship between serotypes 1 and 2 of Haemophilus paragallinarum

Antigenic structure and relationship between serotypes 1 and 2 of Haemophilus paragallinarum were analyzed by the rapid plate agglutination and cross-absorption tests. Encapsulated strain forming iridescent colony type of both serotypes 1 and 2 had at least three antigens: heat-labile and trypsin-sensitive (L), heat-labile and trypsin-resistant (HL), and heat-stable and trypsin-resistant (HS). The L was a major antigen located in a surface and divided serologically into three parts: L1, L2, and L3. The L1 was specifici to serotype 1, the L2 was specific to serotype 2, and the L3 was a common antigen shared by serotypes 1 and 2. The HL and HS were common antigens between serotypes. By trypsinization or heating at 121 C, L antigen lost its agglutinability and agglutinin-producing ability. Nonencapsulated organisms forming noniridescent colony type lacked the L antigen. These results suggested that antigenic structure of H paragallinarum serotypes 1 was L1, L3, HL and HS, while serotype 2 was L2, L3, HL, and HS.