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Association Between Complement Regulatory Protein Factor H and AM34 Antigen, Detected in Senile Plaques

^a First Department of Internal Medicine, Sapporo Medical University, Japan

Fumio Itoh, First Department of Internal Medicine, Sapporo Medical University, South-1, West-16, Chuo-ku, Sapporo, Japan E-mail: fitoh{at}sapmed.ac.jp.

Decision Editor: William B. Ershler, MD

Background. We have previously shown that monoclonal antibody AM34, which is reactive with senile plaques, may recognize the C terminus of complement factor H. In this study, we investigated the expression of factor H in tissue from a human brain and the relation between AM34 antigen and factor H.

Method. Total ribonucleic acid (RNA) was extracted from a normal human brain. A reverse transcriptase-polymerase chain reaction method was employed for detecting messenger RNAs coding for factor H and related proteins. Protein extracts from a normal human brain were also analyzed to detect factor H and related proteins by means of Western blotting. The cerebrospinal fluid from an Alzheimer's disease patient was immunoprecipitated with AM34 and anti-factor-H antibodies, and then it was subjected to gel electrophoresis followed by immunoblotting with AM34 and anti-factor-H antibodies.

Results. 26 clones of complementary DNA fragment were obtained by reverse transcriptase-polymerase chain reaction. Among them, seven clones were identical to factor H, and the others were related proteins and unreported sequences. A Western blot analysis of protein extracts from the normal brain tissue 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 possibly detected in the human brain, and that the AM34 antibody could recognize factor H. Because AM34 is capable of staining senile plaques positively, factor H is suggested to be associated with senile plaques in the human brain.

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