Membrane region of surface IgM is not sufficient for transducing growth inhibitory signals in an immature B cell line WEHI‐231

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Abstract
The murine B lymphoma line WEHI‐231 is representative of immature B cells. Like normal immature B cells, WEHI‐231 is susceptible to growth arrest following cross‐linking of surface IgM (sIgM). Previously, we have shown using a WEHI‐231 immunoglobulin (Ig) δ‐transfectant that sIgD cross‐linking failed to initiate growth arrest, in contrast to sIgM. In this report, we extend our research to investigate the structural requirement of Ig μ chain for regulating growth inhibition. Recombinant, chimeric Ig molecules δ/μm and μ/δm consisting of exons encoding extracellular δ and μ domains and membrane regions of different isotypes were constructed and introduced into WEHI‐231 cells. A similar approach was used for sIgG2b‐expressing transfectants. Our findings indicate that the μm region is not sufficient for regulation of growth inhibition in WEHI‐231 cells and suggest that additional extracellular region(s) of μ chain may be required for this response.