Immunoglobulin glycopeptides from an IgG2b-producing mouse myeloma cell line and from variant cell lines.

A mouse myeloma cell line, 45.6.3, produces an IgG2b immunoglobulin (Ig) with 2 carbohydrate attachment sites on the heavy chains. One site is in the CH2 domain and the other in the VH region. The oligosaccharides at each site have different structures. The ratio of radioactive glucosamine incorporated in the VH compared with the CH2 oligosaccharide is approximately 1 to 3. In an attempt to understand this observation further, variant cell lines derived from 45.6.3 were isolated and their Ig were characterized. A ricin-resistant line, R4R1.5, has the same 2 attachment sites as the wild type, but the ratio of radioactive glucosamine in VH compared with CH2 was 1:1 and not 1:3 as in the wild type. This alteration is most probably due to cellular factors, since the Ig protein is unchanged. The M3.11 cell line produces an Ig with a polypeptide deletion involving the CH3 domain. In this Ig, a 3rd carbohydrate attachment site can be demonstrated. The percentage of radioactivity glucosamine in the CH2 domain compared with the total Ig is about 25% instead of 75% as in the wild type. These results suggest that the extent of glycosylation of different sites on Ig can be affected by both cellular factors and structural changes in the Ig protein.