1. Protein constituents were determined in eight amyloid deposits from eight patients (five male and three female), 53 ± 4 years of age, treated by haemodialysis for 9-20 years using only cuprophane membranes and operated for carpal tunnel syndrome.
2. Soluble proteins were removed by solubilization in phosphate-buffered saline after osmotic lysis. The proteins of the insoluble fibrils were characterized by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and two-dimensional gel electrophoresis, and immunologically identified by Western blotting.
3. In addition to β2-microglobulin, α2-macroglobulin was identified in the fibrillar material. The presence of these two proteins in amyloid deposits was confirmed by immunofluorescent microscopic studies.
4. Our data confirm the presence of β2-microglobulin in haemodialysis-associated amyloidosis, and also suggest a possible role for α2-microglobulin: it may protect β2-microglobulin from proteolytic digestion, leading to its accumulation in intact form and to amyloid fibril formation.