J A Rehmann | PubMed Health

PubMed1994

Transforming growth factor-beta regulates normal human pre-B cell differentiation.

Light chain gene rearrangement during mammalian pre-B differentiation generally occurs in an orderly manner, beginning with kappa genes and proceeding through lambda genes. We have previously shown that human pre-B cell differentiation in vitro leads to a skewing toward lambda expression, resulting in a higher percentage of lambda+ cells than kappa+ cells. We now report that the multifunctional polypeptide transforming growth factor-beta (TGF-beta) exerts a selective inhibitory effect on the acquisition of cell surface lambda light chains during in vitro differentiation of normal human pre-B cells, giving rise to a balanced ratio (approximately 1:1) of kappa+ to lambda+ cells that resembles what normally exists in vivo. The TGF-beta effect was ablated using a neutralizing anti-TGF-beta antiserum and TGF-beta had no significant effect on the acquisition of kappa or surrogate light chains. Experiments using highly enriched pre-B cells (90-95% cytoplasmic mu+) suggested that the TGF-beta effect was directly on the pre-B cell or the pre-B cell to mu+/lambda+ immature B cell transition. The following peptides, cytokines, and antibodies had no effect on light chain acquisition or expression: substance P, vasoactive intestinal peptide, leu/met enkephalin, IL-1, IL-4, IL-7, anti-class II MHC, anti-CD24, anti-CD40, and the CD10 inhibitor phosphoramidon. A selective regulatory role for TGF-beta on normal human B cell development in the bone marrow microenvironment is suggested by these results.

B-Lymphocytes↗

PubMed1993

Unusual patterns of immunoglobulin gene rearrangement and expression during human B cell ontogeny: human B cells can simultaneously express cell surface kappa and lambda light chains.

Immunoglobulin gene rearrangement during mammalian B cell development generally follows an ordered progression, beginning with heavy (H) chain genes and proceeding through kappa and lambda light (L) chain genes. To determine whether the predicted kappa-->lambda hierarchy was occurring 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 alleles in germline configuration, and synthesis/expression of conventional lambda L chains was directly proven by immunoprecipitation/sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in one of them. Thus, human fetal bone marrow B lineage cells harbor the capacity to make functional lambda L chain gene rearrangements without rearranging or deleting either kappa allele. A third unusual cell line, designated 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 rearranged, and a single lambda rearrangement. Immunoprecipitation/SDS-PAGE confirmed that 30.30 cells synthesized and expressed kappa and lambda L chains. Multiparameter flow cytometry was used to demonstrate the existence 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 flow cytometry data was confirmed by two-color immunofluorescence microscopy. The existence of normal human B cells expressing cell surface kappa and lambda refutes the widely accepted concept that expression of a single L chain isotype is immutable. The kappa+/lambda+ cells may represent transients undergoing L chain isotype switching.

B-Lymphocytes↗