Antibodies binding granulocyte-macrophage colony stimulating factor produced by cord blood-derived B cell lines immortalized by Epstein-Barr virus invitro

We detected natural antibodies (auto-Abs) binding human granulocyte-macroph age colony stimulating factor (GM-CSF) in umbilical cord blood (CB) (23 of 94 samples screened) and peripheral blood of women at the end of pregnancy (6 of 42 samples tested). To demonstrate that Abs detected in CB were produ ced by the fetus, CB mononuclear cells were infected with Epstein-Barr viru s in vitro. Ten cell lines producing constitutively anti-recombinant human GM-CSF (rhGM-CSF) Abs were isolated and characterized. These cells displaye d a male karyotype, an early activated B cell phenotype, coexpressed surfac e IgM and IgD, and secreted only IgM with prevailing lambda clonal restrict ion. Specific cell surface binding of biotinylated rhGM-CSF and high-level anti-rhGM-CSF IgM Ab production were typical features of early cell culture s. In late cell passages the frequency of more undifferentiated B cells inc reased. Serum Abs of either maternal or fetal origin or Abs produced in cul ture did not affect the granulocyte and macrophage colony stimulating activ ity of rhGM-CSF from bone marrow progenitors in soft agar, suggesting that the Abs produced were nonneutralizing, (C) 2000 Academic Press.