EVIDENCE FOR COMMON ANTIGENICITY IN THE PILI OF HAEMO PHILUS INFLUENZAE TYPE B (HIB)

Abstract

Antisera to the pilus of a single strain of Hib (C54) were made by hyperimmunization with a pilus-enriched (p+) variant of C54 followed by absorption against a variant of C54 that was identical in encapsulation, outer membrane protein composition, and lipopolysaccharide subtype but lacked pili (p-). 4 different antisera were prepared (2 in different species of mice and 2 in guinea pigs). All 4 antisera agglutinated (aggl) the homologous C54 p+ but did not aggl C54 p-. C54 causes hemagglutination (HA) of human RBCs and adheres well to human epithelial cells (EC) (4.8 bacteria/EC) whereas the p- variant is HA- and adheres poorly (0.2/EC). Addition of antisera resulted in complete inhibition of HA and >60% reduction in C54 bacterial adherence. 9 strains isolated from CSF, blood, and mucosal surfaces were pilus-enriched and studied for cross-reactivity with the pilus of C54. 5 were HA+ with human RBCs only (like C54 and 80% of all Hib isolates), 2 were HA+ with human and rat RBCs (like 12% of all Hib) and 2 were HA+ with all animal and human RBCs tested (like 8% of all Hib). Despite these HA species differences (the only type of heterogeneity found to date) the 4 antisera aggl all 9 strains when p+ but not when p-. Similarly, the antisera inhibited HA of human RBCs and adherence to EC. Thus, pili from different strains of Hib share antigenic determinant(s), and common antipilus antibodies can produce the biologically relevant effect of inhibiting bacterial adherence.