Abstract
The following evidence indicates that C3NeF, a 150,000 dalton protein found in the serum of two-thirds of patients with partial lipodystrophy and one-fifth of those with membrano-proliferative glomerulonephritis, is an immunoglobulin: 1) C3NeF was absorbed by insolubilized anti-IgG, anti-Fc and anti-Fab and was eluted from these absorbents; 2) on isoelectric focussing, C3NeF in 20 patients consisted of multiple bands with pI's around 7.5 and differed from patient to patient; 3) C3NeF crossed the placenta from a patient to her fetus, was associated with low serum C3 concentration in her newborn infant and these abnormalities in the infant disappeared after two weeks; 4) C3NeF had κ antigenic determinants in three patients' serum, had λ determinants in one and in two sera, both. In the present studies insolubilized antisera to IgG1, IgG3 and IgG4 were used to study the subclasses of C3NeF in the serum of five patients.
