Analysis of immunoglobulin chain secretion using hybrid myelomas

Three different approaches have been used to study nonsecreting variants of myeloma and hybrid myeloma lines. Hemolytic plaque assays were used to screen nonsecreting and light (L) chain‐secreting anti‐sheep red blood cell hybrid myeloma variants for reversion to specific antibody or immunoglobulin (Ig) production. No revert ants were detected from among 1.5 × 10 7 −4.2 × 10 7 cells of each line studied. In the absence of a heavy (H) chain, the P3 (MOPC 21) x chain is not secreted but degraded intracellularly. The nature of this secretion defect was investigated in a hybrid myeloma line that produces the P3 x chain and another L chain which is secreted without an H chain, by biochemical studies of the relative distribution of mRNA activity for the two L chains between membrane‐bound and free polysomal fractions. The mutant P3 H chain (H*) produced by the line P3‐NSII/1 is also degraded intracellularly rather than secreted. This defect was complemented by cell fusion of P 3‐NSII/1 to P1, a different Ig‐secreting myeloma line. Mutant H* chains were only secreted as part of hybrid Ig molecules with P1 L chains indicating that the defect in their secretion in the P 3‐ NSII/l line was due to lack of a complementary Ig chain. Additionally, the preferential recovery of P1 H chain loss variants from these hybrids that are producing two H chains and only one L chain, supports the idea that free intracellular H chains have an effect on cell viability and influence the type of variants recovered from hybrid myeloma lines.