Association between complement regulatory protein factor H and AM34 antigen, detected in senile plaques

Background. We have previously shown that monoclonal antibody AM34, which i s reactive with senile plaques. may recognize the C terminus of complement factor II. in this study, we investigated the expression of factor H in tis sue From a human blain and the relation between AM34 antigen and factor H. Method Total ribunucleic acid (RNA) was extracted from a normal human brain . A reverse transcriptase-polymerase chain reaction method was employed fur detecting messenger RNAs coding for factor H and related proteins. Protein extracts from a normal human brain were also analyzed to detect Factor H a nd related proteins by means of Western blotting. The cerebrospinal Fluid f rom an Alzheimer's disease patient war immunoprecipitated with AM34 and ant i-foctor-H antibodies. and then it was subjected to gel electrophoresis fol lowed by immunoblotting with AM34 and anti-factor-H antibodies, Results. 26 clones of complementary DNA fragment were obtained by reverse t ranscriptase-polymerase chain reaction. Among them, seven clones were ident ical to Factor H, and the others were related proteins and unreported seque nces. A Western blot analysis of protein extracts from the normal brain tis sue exhibited a 150-kd band, indicating the presence of factor H. AM34 was immunoreactive with the 150-kd molecule contained in the immunoprecipitates with anti-factor H antibodies, and vice versa. These results suggest that AM34 antigen could be identical to complement factor H. Conclusions. The results of our experiments indicate that Factor H is possi bly detected in the human brain, and that the AM34 antibody could recognize Factor H. Because AM34 is capable of staining senile plaques positively, f actor H is suggested to be associated with senile plaques in the human brai n.