A Mouse Monoclonal Antibody Reactive Preferentially with Human IgM λ

Abstract

In analyzing mouse monoclonal antibodies (mAb) against a human IgM kappa paraprotein, we found an unusual mAb (LP4; gamma 2b kappa isotype) that reacted in an enzyme linked immunosorbent assay with all 5 IgM lambda but not with 8 IgM kappa or other myelomas. Neither isolated mu heavy nor lambda light chains were reactive with LP4 mAb. By immunofluorescence, LP4 mAb identified approximately 30% of IgM+ B cells and approximately 40% of mitogen-stimulated, IgM+ plasma cells from 4-7 normal blood samples. All LP4+ cells were IgM+. Biosynthetic analysis of the plasma cells revealed that LP4 mAb recognized most IgM lambda and a very minor proportion of IgM kappa molecules. This mAb provides a useful marker for the analysis of pre-B and B cell differentiation.

Normal pre-B cells express a receptor complex of mu heavy chains and surrogate light-chain proteins.

“…Surface K or A LC were not detected on the isolated pre-B cells (-99%o purity), whereas ,u chains could be demonstrated in relatively low levels on -25% of the pre-B cells ( Fig. 3 proportion of the pre-B cells (26% ± 5%; seven samples) were reactive with LP4, an antibody that reacts with j chains only when they are associated with conventional A chains or with the / LC complex (27,28).…”

“…After additional clearance with anti-K and anti-A mAbs to remove immunoglobulin products ofpotential B-cell contaminants, the lysates were incubated with either an anti-human IL or an isotype-matched control mAb plus the rat anti-mouse K coupled beads. Immunoprecipitates were analyzed under reducing conditions by SDS/PAGE using 11% acrylamide (27).…”