Baumal R, Scharff M D
J Immunol. 1976 Jan;116(1):65-74.
The IgG2a producing MOPC 173 tumor synthesizes heavy (H) and light (L) chains and assembles them into H2L2 utilizing heavy chain dimers (H2) and H2L as the major precursors. Although the tumor cells secrete only H2L2, they synthesize excess L chains which appear to be degraded and are not secreted. A L chain-producing variant arising spontaneously from the MOPC 173 tumor also failed to secrete any L chains. MOPC 173 tumor cells were cloned in the spleens of normal BALB/c mice and 1 of 23 spleen clones appeared to differ from the parent tumor in demonstrating a) a transient block in the assembly of H2L2 at the H2 level, leading to delayed formation and secretion of H2L2, b) appreciable amounts of non-covalently bonded H2L, c) an abnormal intracellular immunoglobulin species, H4, d) production of equimolar amounts of H and L chains. The patterns of immunoglobulin synthesis and assembly demonstrable in the above studies were also observed when tumor cells were studied in situ. Tryptic peptide mapping of the H and L chains produced by the MOPC 173 tumor and the variant spleen clone failed to demonstrate any differences in the H chains, but there were definite chemical differences in the L chains. These studies indicate that variant myeloma cells producing structurally altered immunoglobulins may continually be arising in myeloma tumors.
产生IgG2a的MOPC 173肿瘤合成重链（H）和轻链（L），并利用重链二聚体（H2）和H2L作为主要前体将它们组装成H2L2。尽管肿瘤细胞仅分泌H2L2，但它们合成过量的轻链，这些轻链似乎被降解且未被分泌。一个从MOPC 173肿瘤自发产生的轻链产生变体也未能分泌任何轻链。MOPC 173肿瘤细胞在正常BALB/c小鼠的脾脏中克隆，23个脾脏克隆中的1个似乎与亲代肿瘤不同，表现为：a）H2L2组装在H2水平出现短暂阻断，导致H2L2形成和分泌延迟；b）有相当数量的非共价结合的H2L；c）一种异常的细胞内免疫球蛋白种类H4；d）产生等摩尔量的H链和L链。当对肿瘤细胞进行原位研究时，也观察到了上述研究中可证明的免疫球蛋白合成和组装模式。对MOPC 173肿瘤和变体脾脏克隆产生的H链和L链进行胰蛋白酶肽图谱分析，未发现H链有任何差异，但L链存在明确的化学差异。这些研究表明，产生结构改变的免疫球蛋白的变体骨髓瘤细胞可能在骨髓瘤肿瘤中不断出现。
