Nonionic block polymer surfactants enhance the avidity of antibodies in polyclonal antisera against Streptococcus pneumoniae type 3 in normal and Xid mice.

Avidities of antibody (sub)classes in polyclonal antisera against Streptococcus pneumoniae type 3 (S3) can be (semi) quantitatively determined with a specific inhibition ELISA. A hexasaccharide was isolated from the hydrolyzed S3 capsular polysaccharide and coupled to a protein-carrier. Mixtures containing these conjugates and nonionic block polymer (NBP) surfactants were used for immunization. After various immunizations of these conjugates without NBP the anti-S3 specific antibodies of IgM and IgG2a isotype decreased in both antibody level and avidity. The adjuvants NBP 1501 and L121 not only enhanced the hexasaccharide-protein induced IgM and IgG antibody levels but also clearly increased the avidity of the two antibody (sub)classes IgM and IgG2a. This effect was observed in normal (data not shown) and X-linked immunodefective mice. A maturation of the IgG antibody response was realized by the second immunization with hexasaccharide-protein conjugate whereas the third immunization showed no further increase in antibody level and avidity.