Fibrillar Assemblage of Variable Segments of Immunoglobulin Light Chains: An Electron Microscopic Study

Abstract

Bence Jones protein was enzymatically cleaved into its variable and constant segments, and then the variable segment was precipitated at neutral pH. The precipitate stained well with Congo red and showed green birefringence under the polarized light after such staining. High resolution electron microscopy of shadow-casted and negatively stained preparations revealed that they consisted of three types of fibrillar structures, respectively measuring 10 to 20 Å, 25 to 40 Å and 75 to 100 Å in width. The thinner fibrillar structures dominated the specimens from earlier stages of the precipitation procedure, while thicker ones predominated in the later samples. The sequential appearance of these structures and other observations suggested that they represented fibrils in different stages of development. These light and electron microscopic aspects of the precipitate have many points corresponding with those of the amyloid, although the identity between the two substances remains to be established. Moreover, the fibrillar structures could be produced in only 3 of 13 Bence Jones proteins treated in an identical fashion.