UNUSUAL PATTERNS OF IMMUNOGLOBULIN GENE REARRANGEMENT AND EXPRESSION DURING HUMAN B-CELL ONTOGENY - HUMAN B-CELLS CAN SIMULTANEOUSLY EXPRESS CELL-SURFACE KAPPA-LIGHT AND LAMBDA-LIGHT CHAINS

Immunoglobulin gene rearrangement during mammalian B cell development generally follows an ordered progression, beginning with heavy (H) cha in genes and proceeding through kappa and lambda light (L) chain genes . To determine whether the predicted kappa-->lambda hierarchy was occu rring in vitro, we generated Epstein-Barr virus-transformed cell lines from cultures undergoing human pre-B cell differentiation. A total of 143 cell lines were established. 24 expressed cell surface mu/lambda by flow cytometry and were clonal by Southern blotting. Surprisingly, two of the mu/lambda-expressing cell lines contained both kappa allele s in germline configuration, and synthesis/expression of conventional lambda L chains was directly proven by immunoprecipitation/sodium dode cyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in one of th em. Thus, human fetal bone marrow B lineage cells harbor the capacity to make functional lambda L chain gene rearrangements without rearrang ing or deleting either kappa allele. A third unusual cell line, design ated 30.30, was observed to coexpress cell surface kappa and lambda L chains associated with mu H chains. The 30.30 cell line had a diploid karyotype, a single H chain rearrangement, both kappa alleles rearrang ed, and a single lambda rearrangement. Immunoprecipitation/SDS-PAGE co nfirmed that 30.30 cells synthesized and expressed kappa and lambda L chains. Multiparameter flow cytometry was used to demonstrate the exis tence of kappa+/lambda+ cells in fetal bone marrow and fetal spleen at frequencies of 2-3% of the total surface Ig+ B cell population. The f low cytometry data was confirmed by two-color immunofluorescence micro scopy. The existence of normal human B cells expressing cell surface k appa and lambda refutes the widely accepted concept that expression of a single L chain isotype is immutable. The kappa+/lambda+ cells may r epresent transients undergoing L chain isotype switching.