Abstract
Streptococcus pneumoniae is a major respiratory pathogen
that causes millions of deaths worldwide. Although subunit
vaccines formulated with the capsular polysaccharides or
their protein conjugates are currently-available, low-cost
vaccines with wide serotype coverage still remain to be developed,
especially for developing countries. Recently, gamma-
irradiation has been considered as an effective inactivation
method
to prepare S. pneumoniae vaccine candidate.
In this study, we investigated the immunogenicity and protective
immunity of gamma-irradiated S. pneumoniae (r-SP),
by comparing with heat-inactivated S. pneumoniae (h-SP)
and formalin-inactivated S. pneumoniae (f-SP), both of which
were made by traditional inactivation methods. Intranasal
immunization of C57BL/6 mice with r-SP in combination
with cholera toxin as an adjuvant enhanced S. pneumoniaespecific
antibodies on the airway mucosal surface and in sera
more potently than that with h-SP or f-SP under the same
conditions. In addition, sera from mice immunized with r-
SP potently induced opsonophagocytic killing activity more
effectively than those of h-SP or f-SP, implying that r-SP
could induce protective antibodies. Above all, immunization
with r-SP effectively protected mice against S. pneumoniae
infection. Collectively, these results suggest that gamma-
irradiation is an effective method for the development
of a killed whole cell pneumococcal vaccine that elicits robust
mucosal and systemic immune responses.
Citations
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