IMMUNOGLOBLIN NATURE OF NEPHRITIC FACTOR (NEF)

Abstract

NeF [human] was antigenically and structurally similar to Ig[immunoglobulin]G by the following experiments. NeF activity in serum was absorbed by and, under acid conditions, could be eluted from anti-myeloma IgG antibody coupled to Sepharose and protein A-Sepharose. Purified NeF could bind to anti-myeloma IgG-Sepharose and could be eluted with acid; this binding was blocked by myeloma IgG. An antibody to .beta.2 microglobulin, showing strong cross-reactivity with normal IgG, bound NeF activity before, but not after, absorption of the antiserum with IgG. Sepharose-coupled antibodies to NeF could bind activity which was recovered in the acid eluate. This binding capacity was lost after absorption of the antibody with normal and myeloma IgG. Structural similarity was demonstrated by pepsin and papain digestion, which resulted in NeF activity eluting with F(ab'')2 and Fab fragments from protein A-Sepharose and Sephadex G-150. Autoradiography of PAGE-SDS [sodium dodecyl sulfate-polyacrylamide gel electrophoresis] of 125I-labeled NeF eluted from .**GRAPHIC**. cells showed that NeF had a larger H chain than normal IgG, sugeesting that NeF might be an abnormal IgG molecule.