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Infection and Immunity, May 2001, p. 3031-3040, Vol. 69, No. 5
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.5.3031-3040.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Increased Immunogenicity and Induction of Class Switching by Conjugation of Complement C3d to Pneumococcal Serotype 14 Capsular Polysaccharide

Samuel T. Test,* Joyce Mitsuyoshi, Charles C. Connolly, and Alexander H. Lucas

Children's Hospital Oakland Research Institute, Oakland, California 94609-1673

Received 24 August 2000/Returned for modification 11 October 2000/Accepted 20 February 2001

Previous studies have demonstrated an adjuvant effect for the C3d fragment of complement C3 when coupled to T-dependent protein antigens. In this study, we examined the antibody response to covalent conjugates of C3d and a T-independent antigen, the capsular polysaccharide of serotype 14 Streptococcus pneumoniae (PPS14). We prepared a conjugate of mouse C3d and PPS14 and compared its immunogenicity with that of a conjugate of PPS14 and ovalbumin (OVA). When BALB/c mice were immunized with PPS14-C3d, there was a significant increase in serum anti-PPS14 concentrations compared with either native PPS14 or control PPS14-glycine conjugates. This was accompanied by a switch in anti-PPS14 from predominantly immunoglobulin M (IgM) to IgG1 by day 25 following primary immunization. Following secondary immunization with PPS14-C3d, there was a marked booster response and a further increase in the ratio of IgG1 to IgM anti-PPS14. Although the primary antibody response to the PPS14-OVA conjugate exceeded that induced by immunization with PPS14-C3d, serum anti-PPS14 concentrations after a second injection of PPS14-C3d were nearly identical to those induced by secondary immunization with PPS14-OVA. Experiments with athymic nude mice suggested that T cells were not required for the adjuvant effect of C3d on the primary immune response to PPS14 but were necessary for enhancement of the memory response after a second injection of PPS14-C3d. These studies show that the adjuvant effects of C3d extend to T-independent antigens as well as T-dependent antigens. As a means of harnessing the adjuvant potential of the innate immune system, C3d conjugates may prove useful as a component of vaccines against encapsulated bacteria.


* Corresponding author. Mailing address: Children's Hospital Oakland Research Institute, 5700 Martin Luther King, Jr. Way, Oakland, CA 94609-1673. Phone: (510) 450-7630. Fax: (510) 450-7910. E-mail: stest{at}chori.org.


Infection and Immunity, May 2001, p. 3031-3040, Vol. 69, No. 5
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.5.3031-3040.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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Copyright © 2001 by the American Society for Microbiology. All rights reserved.