PURIFICATION AND CHARACTERIZATION OF NATURAL ANTIBODIES THAT RECOGNIZE A HUMAN BRAIN LECTIN

We have recently identified oligoclonal IgG antibodies that are relate d to a human brain lectin (HBL14) from serum and cerebrospinal fluid o f patients with neurological disorders. They were termed lectin-like I gG (L-IgG) (Joubert-Caron et al 1994a,b). In this paper, the occurrenc e of antibodies reactive both towards HBL14 and L-IgG was investigated . Binding of antibodies to HBL14 was demonstrated by solid-phase ELISA and chromatography on immobilized HBL14. Fab fragments of these antib odies were also shown to bind to HBL14. The specificity of the antibod ies towards HBL14 was studied using a panel of different antigens. Our data show that individual sera from healthy people as well as a pool of immunoglobulins from 80 blood donors contain an IgG autoreactivity- to HBL14, while no IgM autoreactivity was detected. Anti-HBL14 antibod ies from sera were purified using affinity chromatography on immobiliz ed HBL14. Affinity chromatography further allowed us to demonstrate th at the binding of anti-HBL14 antibodies was mediated through their Fab fragments. A higher amount of anti-HBL14 antibodies was purified usin g a L-IgG-depleted fraction of sera. The binding of anti-HBL14 antibod ies to L-IgG was confirmed by ELISA. Finally, anti-HBL14 antibodies we re found to be polyreactive. These results indicate the occurrence of a novel class of natural antibodies reactive towards a human brain lec tin and suggest that these antibodies may participate in immunoregulat ory mechanisms probably though idiotypic/anti-idiotypic interaction.