Which of the following would MOST likely be found in the Congo red-stained extracellular deposits with the bright green appearance under polarized light?

Amyloidosis occur in a large variety of forms. Primary amyloidosis is one of the more common forms of systemic amyloidosis, and can affect a variety of organs, including the hea, kidney, peripheral nerve, gastrointestinal tract, and respiratory tract. In primary amyloidosis, the amyloid is composed of immunoglobulin light chains, and the disease is now interpreted as a plasma cell disorder closely related to multiple myeloma. This interpretation is clinically significant, as it has led to modern treatments of primary amyloidosis (which formerly had a dismal prognosis) with the chemotherapies designed for multiple myeloma. The treatments are effective only if the disease is recognized and passed to the appropriate specialists as early as possible in the clinical course. Amyloid AA is seen in inflammation-associated amyloidosis and familial Mediterranean fever. Beta-2-microglobulin comprises the amyloid of dialysis-associated amyloidosis. Beta protein precursor comprises the amyloid seen in the brains of patients with Alzheimer's disease and Down syndrome. Ref: Avery T.P., Shah N., Fu W., Weber D.M., Lu G., Lin P., Qazilbash M.H., Wang M. (2011). Chapter 11. Multiple Myeloma and Other Plasma Cell Dyscrasias. In H.M. Kantarjian, R.A. Wolff, C.A. Koller (Eds), The MD Anderson Manual of Medical Oncology, 2e.