LOW FREQUENCY OF CLONAL B CELL EXPANSIONS IN PATIENTS WITH IDIOPATHIC THROMBOCYTOPENIC PURPURA

Abstract

Idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by an increased platelet destruction caused by autoantibodies directed against platelet membrane glycoproteins (GP), most commonly against GPIb/IX, GPIIb/IIIa and GPIa/IIa. In a few recent studies it has been reported that these antibodies frequently have a restricted light chain phenotype, supporting a clonal origin. In this study we wanted to explore the hypothesis of clonal B cell expansions in chronic ITP. We investigated 40 patients (28 women and 12 men) with chronic ITP for clonal B cell expansions using sensitive RT-PCR technique for analysing Ig-gene rearrangements. RNA was isolated from peripheral blood mononuclear cells separated on a Ficoll gradient. The RNA was converted into cDNA and then amplified using FW3 and IgM or IgG specific oligonucleotides to investigate the clonality of B-cells expressing the respective Ig isotype. The PCR fragments were analyzed on sequencing polyacrylamide gels or with an ABI prism 310 DNA analyser. We detected a monoclonal B cell population in only 1 patient and polyclonal rearrangement with one prominent band in 3 patients in the analysis of IgG heavy chain mRNA. The pattern of IgM heavy chain gene rearrangements was polyclonal in all cases. Our study indicates that clonal B-cell expansions are rare in patients with ITP. Most probably, the clonal B-cell expansion responsible for the production of autoantibodies in ITP, if present, is below the detection limit.