Precipitating antibodies against Neisseria meningitidis in normal sera and their possible origin.

Crossed immunoelectrophoresis was used to study precipitating antibodies against Neisseria meningitidis in sera from 214 normal persons and in human gammaglobulin. A polyspecific meningococcal antigen preparation and a corresponding rabbit antiserum constituted the reference system. All the sera contained one to five precipitins against N. meningitidis which could be identified and quantified by means of the reference system. The precipitin score, which expresses the number and titre of precipitins in each serum, increased with age. More than 25 precipitins were found in the gammaglobulin preparation, including antibodies against the groupspecific polysaccharides A, B and C. Absorption of three of the five normally occurring precipitins (nos. 4, 19, 22) with antigens from various bacteria showed that precipitins nos. 4 and 19 could be completely absorbed by antigens from other Neisseria species, but not by antigens from other genera. This indicates that these two precipitins may have been induced by non-pathogenic Neisseria species or by meningococci. The finding of protective antibodies in gammaglobulin might indicate the possibility of its use in prophylaxis or therapy meningococcal infections.