The unspecific antibody response to N. meningitidis group A capsular polysaccharide often seen in bacteraemic diseases.

When studying acute and convalescent phase sera of patients with bacteraemic diseases, an unexpected rise of antibody activity (measured as binding of radioactive antigen) towards the capsular polysaccharide of Neisseria meningitidis group A (MenA) was observed in 59 out of 292 patients whose infection was caused by other organisms (other groups of N. meningitidis, Haemophilus influenzae, Streptococcus pneumoniae, Escherichia coli or Staphylococcus aureus). This non-specific reaction was not seen in non-bacteraemic diseases (Mycoplasma pneumonia, viral meningitis) or after immunization with H. influenzae type b capsular polysaccharide or Salmonella and cholera whole cell vaccines. The 'unspecific' anti-MenA antibodies were of all immunoglobulin classes A, G and M tested, and had lower avidity than did those in the specific response. They were clearly inhibitable by N-acetylmannosamine which inhibited the specific antibodies only marginally.