Mouse pre-B cells synthesize and secrete mu heavy chains but not light chains.
The immunoglobulins produced by the earliest recognizable B cell precursors (pre-B cells) were characterized in the mouse and human. Immunofluorescent analysis revealed no evidence of surface IgM components, and only mu heavy chains could be detected intracytoplasmically in pre-B cells. Surface IgM components could not be isolated from intact fetal liver cells that lacked sIgM+ B lymphocytes but possessed pre-B cells. Pre-B cells were shown to synthesize and secrete mu heavy chains but not light chains by immunochemical analysis. These mu chains constituted less than 0.01% of TCA precipitable protein synthesized and secreted by fetal liver cells during an 8 hr labelling period. Migration of both intracellular and secreted mu chains on SDS-PAGE suggested that they were smaller than mu chains secreted by mouse and human plasmacytomas. These data indicate that mu chain synthesis precedes light chain expression during B cell ontogeny and suggest a new role for pre-B cells in the generation and expression of a diverse immunoglobulin repertoire.
D000361:Agammaglobulinemia / Q000276:immunology; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D003571:Cytochalasin B / Q000494:pharmacology; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis*; D007147:Immunoglobulin Light Chains / Q000096:biosynthesis*; D007075:Immunoglobulin M / Q000096:biosynthesis; D007148:Immunoglobulin mu-Chains / Q000032:analysis / Q000096:biosynthesis*; D008099:Liver / Q000166:cytology; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D011947:Receptors, Antigen, B-Cell / Q000096:biosynthesis
D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D007075:Immunoglobulin M; D007148:Immunoglobulin mu-Chains; D011947:Receptors, Antigen, B-Cell; D003571:Cytochalasin B