Antibodies to the capsular polysaccharide of Neisseria meningitidis group B or E. coli K1 bind to the brains of infant rats in vitro but not in vivo.

The binding of monoclonal and polyclonal IgG antibodies specific to the capsular polysaccharide of Neisseria meningitidis group B and E. coli K1 was tested to the cross-reacting polysialosyl structures previously shown to be present in the brain of infant rats (Lancet 1983; ii: 355-7). Strong immunofluorescence was obtained after in vitro incubation of the brains of 1 to 13 days old rats with the antibodies whereas the brains of adult rats remained negative. The number of antibody-binding structures decreased as a function of age, being highest at the age of 1 to 5 days. However, when the same antibodies were injected intraperitoneally into the infant rat, or into the mother rat 2 days before parturition, no binding of antibodies to the infant rat brain tissue was observed.