title: Truncation of the mu heavy chain alters BCR signalling and allows recruitment of CD5+ B cells.
abstract: Ig are multifunctional molecules with distinct properties assigned to individual domains. To assess the importance of IgM domain assembly in B cell development we generated two transgenic mouse lines with truncated muH chains by homologous integration of the neomycin resistance gene (neo(r)) into exons C(mu)1 and C(mu)2. Upon DNA rearrangement shortened muH chain transcripts, V(H)-D-J(H)-C(mu)3-C(mu)4, are produced independent of the transcriptional orientation and termination signals provided by neo(r). The truncated muH chain of approximately 52 kDa associates non-covalently with the L chain to form a monovalent HL heterodimer. Surface IgM is assembled into a defective BCR complex which has lost important signalling capacity. In immunizations with T-dependent and T-independent antigens, specific IgM antibodies cannot be detected, whilst IgG responses remain normal. B cell development in the bone marrow is characterized by an increase in early B cells, but a decrease of B220(+) cells from the stage when muH chain rearrangement is completed. The peritoneal lymphocyte population has elevated levels of CD5(+) B cells and their expansion may be the result of a negative feedback mechanism. The results show that antigenic stimulation is compromised by truncated monovalent IgM and that this deficit in stimulation leads to reduced levels of conventional B-2 lymphocytes, but dramatically increased levels of B-1 cells.
authors.affiliation: Laboratory of Developmental Immunology, The Babraham Institute, Babraham, Cambridge CB2 4AT, UK.
authors.forename: X
authors.initials: X
authors.lastname: Zou
authors.forename: C
authors.initials: C
authors.lastname: Ayling
authors.forename: J
authors.initials: J
authors.lastname: Xian
authors.forename: T A
authors.initials: TA
authors.lastname: Piper
authors.forename: P J
authors.initials: PJ
authors.lastname: Barker
authors.forename: M
authors.initials: M
authors.lastname: Brüggemann
mesh_terms: D017398:Alternative Splicing / Q000276:immunology; D000818:Animals; D000918:Antibody Specificity / Q000235:genetics; D016175:B-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism / Q000473:pathology; D001483:Base Sequence; D001854:Bone Marrow Cells / Q000276:immunology / Q000473:pathology; D018956:CD5 Antigens / Q000096:biosynthesis*; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology; D018985:Epitopes, B-Lymphocyte / Q000235:genetics; D005822:Genetic Vectors / Q000138:chemical synthesis; D007127:Immunoglobulin Constant Regions / Q000235:genetics; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis / Q000235:genetics*; D007147:Immunoglobulin Light Chains / Q000235:genetics; D007075:Immunoglobulin M / Q000096:biosynthesis / Q000235:genetics; D007148:Immunoglobulin mu-Chains / Q000096:biosynthesis / Q000235:genetics*; D008213:Lymphocyte Activation / Q000235:genetics; D018655:Lymphocyte Count; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D011947:Receptors, Antigen, B-Cell / Q000037:antagonists & inhibitors / Q000502:physiology*; D017384:Sequence Deletion / Q000276:immunology*; D015398:Signal Transduction / Q000235:genetics* / Q000502:physiology; D013154:Spleen / Q000276:immunology / Q000473:pathology; D015854:Up-Regulation / Q000235:genetics / Q000276:immunology
chemical_list: D018956:CD5 Antigens; D018985:Epitopes, B-Lymphocyte; D007127:Immunoglobulin Constant Regions; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D007075:Immunoglobulin M; D007148:Immunoglobulin mu-Chains; D011947:Receptors, Antigen, B-Cell