Activity of flagellar antibody in the phagocytosis of pseudomonas aeruginosaby polymorphonuclear leukocytes

The H (flagellar) antigen of Pseudomonas aeruginosa isolates is expressed as either a homologous (b) or heterologous (a₀a₁a₂a₃a₄) type. P. Aeruginosa rabbit anti-flagellar IgG was shown to enhance phagocytosis of P. Aeruginosa by mouse peritoneal polymorphonuclear leukocytes (PMNs) In two different phagocytosis assays. An indirect assay was initially used in which the decrease in viable bacterial counts from the supernatant of a mixture consisting of bacteria and PMNs was measured. The results were confirmed and extended using an assay in which bacteria were labeled by growth in [³H] thymidine, and radioactive counts of internalized bacteria were recorded. With this method, intracellular bacteria were quantitated directly. The opsonic activity of the flagellar antibody was specific for the flagella type (a or b). It was shown that P. Aeruginosa strain M-2 (b-type) antiserum Increased opsonophagocytosis of strain PAO1 (b-type) by seven-fold over normal rabbit serum (MRS), whereas a-type antiserum was essentially unreactive. To ascertain the degree of opsonic cross-reactivity between heterologous a-types, four different strains were used: 1210 (a₀a₁a₂), 170018 (a₀a₃a₄), 5940 (a₀a₂), and SBI-N (a_X). Using 1210 antiserum, it was shown that all four a-types were phagocytized specifically at a level four to six fold over NRS. In contrast, M-2 antiserum was not opsonic. The opsonic property of flagellar antiserum and the demonstration of cross-reactivity among a-types further supports previous evidence favoring the use of only two H antigen types (a and b) in a potential vaccine.