Equine cutaneous amyloidosis derived from an immunoglobulin lambda-light chain. Immunohistochemical, immunochemical and chemical results.

The research paper discusses the findings of a study on the classification and identification of amyloid deposits from cutaneous nodular amyloidosis in horses, confirming that the equine version (eA lambda) is derived from an immunoglobulin lambda-light chain, similar to cases previously identified in humans and cats.

Overview of the Study

• The study works on the characterization and categorization of amyloid deposits from a specific skin disease in horses, known as cutaneous nodular amyloidosis. The associated condition for this skin disease is extramedullary plasmacytoma, a form of plasma cell cancer.
• The deposits identified were found to be derived from the equine immunoglobulin lambda-light chain, an element of the equine immune system. The deposits are therefore named as eA lambda (HIP).

Methodology

• The proteins associated with the disease were broken down and separated using a chemical process involving Sephadex G-100 in 6M guanidine.HCl.
• Following separation, the proteins were further examined using polyacrylamide gel electrophoresis, which helped to identify key polypeptides weighing 24 kDa and 50 kDa.
• These polypeptides were shown to have a significant number of immunoglobulin lambda-antigenic determinants as ascertained by immunodiffusion and immunoblotting.
• Some proteins were found to have a “blocked” N-terminus. To study these further, they were treated with trypsin and endoproteinase Asp-N and then isolated using reversed-phase high-performance liquid chromatography (a form of protein purification).
• Seven peptides were then subjected to automatic amino-acid sequence determination, revealing several novel sequences.

Key Findings

• The results showed that these peptides originated from a monoclonal immunoglobulin lambda-light chain and a gamma-heavy chain after comparing their sequences with a data bank.
• Since the light chain was the predominant component in a virtually pure amyloid fibril preparation, it was considered the leading amyloidogenic (amyloid-causing) polypeptide.
• It was therefore concluded that immunoglobulin lambda-light chain-derived amyloidosis, which has also been observed in humans and cats, is now identifiable in horses.