Two spontaneous BALB/c lymphomas synthesize IgM: Monomers and half molecules are isolated and characterized whereas another molecule resembles IgD

Spontaneous lymphomas of BALB/c mice, both in vivo tumors and cell lines established in long term tissue cultures, were investigated for their ability to synthesize IgM by using radiolabeled amino acid precursors. Immunoglobulins manufactured by lymphomas K46 and L10A had the m.w. of monomeric IgM and IgM half molecule. Both of these molecules could be immunoprecipitated with class specific anti-IgM but not anti-IgA or anti-IgG. When precipitated with polyvalent anti-Ig L10A synthesized monomeric immunoglobulins that migrated as two peaks in contrast to their single counterpart precipitated with anti-IgM. The secnd peak migrated in the region expected for IgD. Monomer and half molecules were composed of similar ratios of μ chains to light chains linked by disulfide bonds. The μ₂L₂ monomer of these B cell lines migrated slightly slower in SDS PAGE than a μ₂L₂ secreted by a myeloma. Thus, these lymphomas synthesize immunoglobulins with the chemical and antigenic characteristics typical of monomeric membrane attached IgM and IgM half molecules, plus a molecule resembling IgD and L10A only. Lymphoma assembly of monomeric IgM may follow the same initial biosynthetic sequence as myeloma assembly.