Nature of yellow-brown bodies. Histochemical and ultrastructural studies on the brown pigment.

Yellow-brown bodies were observed in the sinusoids of lymph nodes and in histiocytes. The authors examined their histochemical characteristics. They were similar to lipofuscin pigments in the liver. However, ultrastructurally, yellow-brown bodies were different from lipofuscin and melanin pigments. The electron microscopic investigation suggested that degradation products of yellow-brown bodies in histiocytes resemble brown pigments in the black thyroid.