Human IgM Anti-IgM Cytotoxin for B Lymphocytes

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Abstract
B [bone marrow-derived] lymphocytes are killed at 5.degree. C by some autologous and allogeneic human sera. Such cold cytotoxins are directed against immunoglobulins on the surface of B lymphocytes. The activity is partially removed by passing serum through Ig[immunoglobulin]G-coupled Sepharose and usually completely removed by passing serum through IgM-coupled Sepharose. Activity is regained from the columns by acid elution and IgM inhibits the cytotoxicity of these eluates. 125I-labeled eluates bind to IgG- and IgM-coupled Sepharose beads and binding is inhibited by IgM and to a lesser degree by IgG thus showing a primarily more avid binding to IgM as compared to IgG. The 125I-labeled cytotoxic eluates recognize the same determinant(s) on IgM and IgG. IgM anti-IgM antiimmunoglobulin may regulate immune reactivity by binding to B lymphocyte surfaces.