Hemodialysis: demonstration of truncated beta 2-microglobulin in AB-amyloid in situ

Amyloid deposits of patients on long-term hemodialysis consist of a considerable proportion of beta 2-microglobulin (beta 2m) fragments, as demonstrated by N-terminal amino acid sequence analysis of isolated amyloid fibril proteins. Since this finding may have pathogenetic relevance, we have produced fragment-specific antibodies directed against a synthetic peptide of beta 2m (P132) commencing at position 20. Absorption of this antiserum on insolubilized beta 2m and subsequent isolation of the anti-P132 antibody from the insolubilized P132 peptide yielded a cleavage site-specific antibody which reacted only with P132, but not with a control fragment of beta 2m and only marginally with a beta 2m preparation in micro-ELISA. When applied onto tissue sections from various organs with AB-amyloid using an immunoperoxidase method, the fragment-specific anti-P132 antibody reacted immunohistochemically predominantly with renal AB-amyloid stones, but not with all amyloid from large joints and bone marrow amyloid-tumors, in contrast to an anti-AB or beta 2m-antibodies, which intensely stained all deposits. Thus, the presence of fragmented beta 2m-molecules have been demonstrated in amyloid in tissue sections. These data are in accordance with the results of chemical studies.