A Mouse Monoclonal Antibody Reactive Preferentially with Human IgM λ

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Abstract
In analyzing mouse monoclonal antibodies (mAb) against a human IgMκ paraprotein, we found an unusual mAb (LP4; γ2bκ isotype) that reacted in an enzyme linked immunosorbent assay with all 5 IgMλ but not with 8 IgMκ or other myelomas. Neither isolated μ heavy nor λ light chains were reactive with LP4 mAb. By immunofluorescence, LP4 mAb identified ~30% of IgM+ B cells and ~40% of mitogen-stimulated, IgM+ plasma cells from 4-7 normal blood samples. All LP4+ cells were IgM+. Bios ynthetic analysis of the plasma cells revealed that LP4 mAb recognized most IgMλ and a very minor proportion of IgMκ molecules. This mAb provides a useful marker for the analysis of pre-B and B cell differentiation.