SYNTHESIS, ASSEMBLY, AND SECRETION OF GAMMA GLOBULIN BY MOUSE MYELOMA CELLS : III. ASSEMBLY OF THE THREE SUBCLASSES OF IGG

The synthesis, assembly, and secretion of the three major subclasses of mouse IgG has been examined in 14 myeloma tumors and two cultured cell lines as well as in the cells from the popliteal lymph nodes of immunized mice. The total amount of IgG synthesized was between 15 and 43% of the cytoplasmic proteins made during a 15 min period. H2 and H2L were the major precursors of IgG2a and IgG1 but, in all of the tumors, HL was also an intermediate. In contrast, HL was a major precursor of IgG2b. Most of the noncovalent and covalent assembly of IgG occurred after release of the newly synthesized H and L chains from the polyribosomes and assembly was not completed until 10 min or more after the synthesis of the polypeptide chains

Abnormalities in the NC1 domain of collagen type IV in GBM in canine hereditary nephritis

Abnormalities in the NC1 domain of collagen type IV in GBM in canine hereditary nephritis. Samoyed hereditary glomerulopathy (SHG) in dogs serves as a model for human X-linked hereditary nephritis (HN). We previously showed that glomerular capillaries of affected males did not stain by immunofluorescence (IF) using serum from a patient with Goodpasture's syndrome. Our goal in the present study was to determine whether the NC1 domain of the collagen type IV molecule, which contains Goodpasture antigen (GPA), could be demonstrated in these dogs, and to assess its immunological reactivity. By SDS-PAGE, NC1 in collagenase digests of glomerular basement membranes (GBM) of unaffected and carrier female dogs in the family with SHG showed 24 kilodalton (kD), 26 kD and 28 kD monomer, and 46 kD and 47 kD dimer components, but the 24 kD monomer was diminished in the affected males. By IF, a rabbit antibody to NC1 stained glomerular capillaries of unaffected, affected male, and carrier female dogs. In contrast, a human anti-GBM plasmapheresis fluid (PPF) stained glomerular capillaries of only the unaffected and carrier female dogs. By RIA, both antibodies reacted strongly with NC1 in collagenase digests of GBM of the unaffected and carrier female dogs, but showed reduced reactivity with NC1 of affected males. By Western blotting, both antibodies bound to dimers and 24 kD and 26 kD monomers of the NC1 domain in collagenase digests of GBM of unaffected and carrier female dogs. However, in affected males, the rabbit anti-NC1 antibody did not bind to the 24 kD monomer, while the human anti-GBM PPF showed weak binding to the 24 kD and 26 kD monomers. Hence, although the NC1 domain could be detected in GBM of affected male dogs, a reduced amount of the 24 kD monomer was present and, as well, the 26 kD monomer possessed altered immunological reactivity. These two monomers are known to be derived from separate autosomal gene products in man. Hence, our studies raise the possibility that, in SHG and X-linked HN, the underlying defect may involve a protein which is coded on the X chromosome and is involved in modifying the collagen type IV molecule