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Infect. Immun., 12 1997, 5010-5016, Vol 65, No. 12
M Akkoyunlu, A Melhus, C Capiau, O van Opstal and A Forsgren
The nonacylated form of protein D (PDm) of Haemophilus influenzae has been
shown to induce the production of antibodies that are bactericidal to
homologous and heterologous nontypeable H. influenzae (NTHi) strains. In
this study, immunization of rats with lipoprotein D (LPD) induced higher
levels of anti-protein D immunoglobulin G and A serum antibodies than
immunization with PDm, and the bactericidal activities of sera from
LPD-immunized rats were greater than those of sera from PDm-immunized rats.
Immunization with LPD or PDm did not prevent the development of acute
otitis media (AOM) when rats were challenged with 10(4) CFU of an NTHi
strain. However, on the eighth day of bacterial challenge, 50% (5 of 10) of
LPD-immunized rats had recovered from otitis media and 30% (3 of 10) had
negative middle ear cultures, whereas only 30% (3 of 10) of PDm-immunized
rats had recovered, though none was culture positive. Immunization with an
inactivated homologous bacterial strain elicited 70% protection (i.e., 7 of
10 rats) in the rat otitis media model. LPD and PDm were also conjugated to
the H. influenzae type b (Hib) capsular polysaccharide, polyribosyl ribitol
phosphate (PRP), to test protein D-conjugated PRP vaccine's potential for
protection against Hib infection. When two LPD-conjugated and two
PDm-conjugated PRP vaccines, each containing a different protein
concentration, and a tetanus toxoid-conjugated vaccine (ACT-HIB) were
tested in the experimental model of rat otitis induced with a Hib strain
(Minn A), both of the LPD-conjugated and one of the PDm- conjugated
vaccines induced significant protection from AOM, the level of protection
being highest in animals given the vaccine with the highest LPD content.
Sera from these rats also manifested the highest anti-PRP and anti-LPD
antibody levels and the highest bactericidal activities against a Hib
strain and an NTHi strain.
Copyright © 1997, American Society for Microbiology
The acylated form of protein D of Haemophilus influenzae is more immunogenic than the nonacylated form and elicits an adjuvant effect when it is used as a carrier conjugated to polyribosyl ribitol phosphate
Department of Medical Microbiology, University of Lund, Malmo University Hospital, Sweden. Mustafa.Akkoyunlu@Yale.edu
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