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Infect Immun, August 1998, p. 3719-3726, Vol. 66, No. 8
Channing Laboratory, Department of Medicine,
Brigham and Women's Hospital, Harvard Medical School, Boston,
Massachusetts 02115-5804
Received 17 February 1998/Returned for modification 7 April
1998/Accepted 24 May 1998
The O antigen of the Pseudomonas aeruginosa
lipopolysaccharide is the optimal target for protective antibodies, but
the unusual and complex nature of their sugar substituents has made it
difficult to define the range of these structures needed in an
effective vaccine. Most clinical isolates of P. aeruginosa
can be classified into 10 O-antigen serogroups, but slight chemical
differences among O polysaccharides within a serogroup give rise to
subtype epitopes. These epitopes could impact the reactivity of
O-antigen-specific antibodies, as well as the susceptibility of a
target strain to protective, opsonic antibodies. To define parameters
of serogroup and subtype-epitope immunogenicity, antigenicity, and
surface expression on P. aeruginosa cells, we prepared
high-molecular-weight O-polysaccharide vaccines from strains of
P. aeruginosa serogroup O2, for which eight structurally
variant O antigens expressing six defined subtype epitopes (O2a to O2f)
have been identified. A complex pattern of immune responses to these
antigens was observed following vaccination of mice. The
high-molecular-weight O polysaccharides were generally more immunogenic
at low doses (1 and 10 µg) than at a high dose (50 µg) and usually
elicited antibodies that opsonized the homologous strain for phagocytic
killing. Some of the individual polysaccharides elicited cross-opsonic
antibodies to a variable number of strains that express all of the
defined serogroup O2 subtype epitopes. Combination into one vaccine of
two antigens that individually elicited cross-reactive opsonic
antibodies to most members of the O2 serogroup inhibited, instead of
enhanced, the production of antibodies broadly reactive with most
serogroup O2 subtype strains. Thus, immune responses to P. aeruginosa O antigens may be restricted to a limited range of
epitopes on structurally complex O antigens, and combining multiple
related antigens into a single vaccine formulation may inhibit the
production of those antibodies best able to protect against most
P. aeruginosa strains within a given O-antigen serogroup.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Complex Serology and Immune Response of Mice to
Variant High-Molecular-Weight O Polysaccharides Isolated from
Pseudomonas aeruginosa Serogroup O2 Strains
*
Corresponding author. Mailing address: Channing
Laboratory, 181 Longwood Ave., Boston, MA 02115-5804. Phone: (617)
525-2269. Fax: (617) 731-1541. E-mail:
gpier{at}channing.harvard.edu.
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