Systemic AL Amyloidosis in a Cat

Abstract

A tarsal mass removed from a 10 year old cat proved to be an extramedullary plasmacytoma which was largely composed of amyloid. Subsequent histological examination at necropsy indicated amyloid was also present in lymph nodes, spleen, and liver. Amyloid fibrils isolated from the tarsal mass were reduced, alkylated, and fractionated on Sepharose CL6B in 4M guanidine hydrochloride. The subunit protein was digested with trypsin or Staphylococcus protease, and the resulting peptides were fractionated by reverse phase HPLC. Sequence analysis of the tryptic peptides showed that the amyloid subunit protein was derived from an immunoglobulin lambda light chain. The variable region framework sequence resembled most closely the human lambda II subgroup. This represents the first structurally characterized immunoglobulin amyloid protein in a species other than human.