A recombinant non-fatty acylated form of the Hi-PAL (P6) protein of Haemophilus influenzae elicits biologically active antibody against both nontypeable and type b H. influenzae

An approximately 15,000-dalton outer membrane lipoprotein of Haemophilus influenzae, the Hi-PAL (P6) protein, has been shown to elicit bactericidal and protective antibodies against both type b and nontypeable H. influenzae strains and is a vaccine candidate for these organisms. To determine whether the lipid modification of this protein is required for immunogenicity or the elicitation of biologically active antibodies, a genetic fusion was constructed that contains the sequence of mature Hi-PAL fused to the polylinker region of pUC19. The protein expressed by this clone does not contain detectable lipid and was purified to homogeneity. This recombinant fusion protein, rPAL, elicited a strong immune response when injected into rabbits, and the antiserum reacted well with native Hi-PAL. The antiserum was bactericidal against a number of clinical nontypeable strains, duplicating the activity of anti-Hi-PAL. The anti-rPAL antiserum was also protective against type b bacteremia in the infant rat model. These results demonstrate that purified rPAL elicits antibodies with biological activities that are similar to those of anti-Hi-PAL antibodies. Thus, the lipid component of Hi-PAL is not required for either immunogenicity or elicitation of biologically active antibodies.