Transcript expression of two Iglambda rearrangements and RAG-1/RAG-2 in a mature human B cell producing IgMlambda islet cell autoantibody.
A human B cell clone, EBV-MB91, producing IgMlambda islet cell autoantibody (ICA), obtained by Epstein-Barr virus (EBV) transformation of peripheral CD5- surface Ig+ B cells from a Type 1 diabetic child, and an EBV-MB91-derived hetrohybridoma, HY-MB91, were analyzed for rearranged Ig genes. Both EBV-MB91 and HY-MB91 contained and expressed a unique IgH chain rearrangement (unmutated VH5-51-D6-19-JH5) but contained and expressed two Iglambda chain rearrangements: (i) Vlambda1-4-Jlambda3-Clambda3, which encoded the Iglambda chains (pI, 8.0) of IgMlambda-ICA, showing few mutations but consistent with Ag-driven selection according to the multinomial probability model; and (ii) Vlambda4-1-Jlambda3-Clambda3, with more mutations but inconsistent with antigen-driven selection and involving stop codons that precluded Iglambda synthesis. HY-MB91 showed a progressive loss of IgMlambda-ICA secretion, which was coupled with transcripts of the aberrant Vlambda4-1-Jlambda3-Clambda3 predominating (1.7-fold) over those of Vlambda1-4-Jlambda3-Clambda3. EBV-MB91 also showed the loss of IgMlambda-ICA secretion, associated with cell death. RAG-1 and RAG-2 transcripts occurred in EBV-MB91 but not in HY-MB91, indicating that the former but not the latter might have been able to exhibit V(D)J recombinase activity. Data show that a mature nonmalignant human B cell clone producing IgMlambda-ICA can express RAG-1/RAG-2 transcripts. That the aberrant Vlambda4-1-Jlambda3-Clambda3 was a nonproductive rearrangement occurring at the pre-B cell stage cannot be excluded. However, the hypothetical possibility that one of the two rearrangements corresponded to a secondary rearrangement occurring in the mature B cell represented by the EBV-MB91 clone might also be considered and is discussed.
Benito
Carmen
C
Endocrinology and Diabetes Service, Hospital Clínic Universitari, IDIBAPS, Faculty of Medicine, University of Barcelona, Villarroel 170, 08036 Barcelona, Spain.
Gomis
Ramon
R
Fernández-Alvarez
Josefa
J
Usac
Elena F
EF
Gallart
Teresa
T
D001323:Autoantibodies / Q000096:biosynthesis*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D001483:Base Sequence; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000235:genetics*; D003922:Diabetes Mellitus, Type 1 / Q000473:pathology; D015321:Gene Rearrangement; D005803:Genes, Immunoglobulin / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D006825:Hybridomas; D007075:Immunoglobulin M; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D012333:RNA, Messenger / Q000096:biosynthesis
D001323:Autoantibodies; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D007075:Immunoglobulin M; D009687:Nuclear Proteins; C499311:RAG2 protein, human; D012333:RNA, Messenger; C064655:V(D)J recombination activating protein 2; C024211:islet cell antibody; C064658:RAG-1 protein