Phagocytic inhibitory activity in serum of cats immunized withPseudomonas aeruginosa lipopolysaccharide

Abstract

Sequentially collected sera from cats chronically immunized withPseudomonas aeruginosa lipopolysaccharide (LPS) serotype 5 were assessed for their effect on phagocytosis by alveolar macrophages from nonimmunized cats. Phagocytosis was measured by incubating macrophage monolayers for 20 min in the presence of3H-labeled bacteria and 5% serum from control or immunized animals. Sustained phagocytic inhibitory activity developed in the sera of eight of 11 immunized cats (mean inhibition ranged from 30% to 73%) after 13 weekly immunizations. The activity was specific because phagocytosis ofStaphylococcus aureus andP. aeruginosa of another serotype (type 6) was unimpaired. An enzyme-linked immunosorbent assay showed an increase in the amount of LPS-specific IgG in postimmunization sera from the eight cats with inhibitory activity. The IgG appeared to be serotype specific because significantly higher titers were obtained against LPS serotype 5 than LPS serotype 6. The results suggest that phagocytic inhibitory activity in sera from LPS-immunized cats may be due to anti-LPS IgG.