Immunoglobulin synthesis in the human myeloma cell line U‐266; expression of two immunoglobulin heavy chain isotypes (ϵ and α) after long‐term cultivation in vitro

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Abstract
A human IgE‐producing myeloma has been cultivated in vitro as a continuous cell line (U‐266) since 1968. Analysis of immunoglobulin production during early passages of the cell line demonstrated a high synthesis rate of monoclonal IgE. Analysis of late passages, cultivated after 1980, revealed a 3‐6‐fold lower rate of IgE secretion, This decrease was accompanied by the appearance of small amounts of IgA in the culture medium together with IgE. RNA was extracted from a late passage of U‐266 and analyzed by Northern blotting, using ϵ and α‐specific oligonucleotides as hybridization probes. The results showed the presence of ϵ as well as α‐specific mRNA. Moreover the results demonstrated that the latter mRNA was derived from the α2 locus and that the ϵ and the α2‐specific mRNA contained the same V region sequences. Southern blot analysis of DNA from the late passage of the U‐266 cell line failed to reveal a recombinatory switch from the ϵ locus to the α2 locus. The expression of α2 is thus likely to be caused by differential splicing rather than by an isotype switch at the DNA level.