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Infect Immun, June 1998, p. 2866-2870, Vol. 66, No. 6
Departments of Immunology,1
Pediatrics,2 and
Microbiology,4
National
University Hospital,
Received 30 December 1997/Returned for modification 5 February
1998/Accepted 25 March 1998
Streptococcus pneumoniae is a major respiratory
pathogen of infants, children, and the elderly. Polysaccharide vaccines
have been useful in adult populations but do not elicit protective immunity in infants and young children. To enhance their
immunogenicity, vaccines of pneumococcal polysaccharides conjugated to
proteins are being developed. In this study antibody levels and opsonic activities were compared in sera of infants and adults injected with
pneumococcal polysaccharide type 6B (Pn6B) conjugated to tetanus toxoid
(TT) (Pn6B-TT). Healthy infants were injected with Pn6B-TT; group A was
injected at 3, 4, and 6 months of age, and group B was injected at 7 and 9 months of age. A booster injection was given at 18 months. Adults
were injected once. Antibodies were measured by enzyme-linked
immunosorbent assay and radioimmunoassay, and their functional
activities were measured by opsonophagocytosis of radiolabelled
pneumococci. In adults, increases in immunoglobulin M (IgM), IgG, IgA,
IgG1, and IgG2 to Pn6B were observed. Infants reached adult levels of
IgG1 anti-Pn6B after the primary injections. After the booster
injection the infant groups had total IgG- and IgM-Pn6B antibody levels
similar to those of adults. After the booster injection, IgG1 was the
dominant infant anti-Pn6B isotype and at a level higher than in
vaccinated adults, but IgA and IgG2 antibodies remained at very low
levels. Opsonic activity increased significantly after Pn6B-TT
injections; the highest infant sera showed opsonic activity comparable
to that of vaccinated adults. Overall, opsonic activity correlated best
with total and IgG anti-Pn6B antibodies (r = 0.741, r = 0.653, respectively; n = 35) and
was highest in sera with high levels of all Pn6B antibody isotypes. The
results indicate the protective potential of a pneumococcal 6B
polysaccharide protein conjugate vaccine for young infants.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Isotypes and Opsonophagocytosis of Pneumococcus
Type 6B Antibodies Elicited in Infants and Adults by an Experimental
Pneumococcus Type 6B-Tetanus Toxoid Vaccine

*
Corresponding author. Mailing address: Department of
Immunology, National University Hospital, 101 Reykjavik, Iceland.
Phone: 354 560 1962. Fax: 354 560 1943. E-mail:
ingileif{at}rsp.is.
Present address: Department of Immunology, University Hospital
Utrecht (AZU), 3584 CX Utrecht, The Netherlands.
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