Reduced tumour necrosis factor receptor superfamily 13C inversely correlated with tumour necrosis factor superfamily 13B in patients with immune thrombocytopenia.

To investigate the expression of tumour necrosis factor superfamily 13B (TNFSF13B) receptors in immune thrombocytopenia (ITP) and their correlation with disease activity, we investigated the protein and mRNA levels of TNFSF13B, tumour necrosis factor receptor superfamily 13C (TNFRSF13C), TNFRSF13B and TNFRSF17 by flow cytometry, enzyme-linked immunosorbent assay and real time quantitative polymerase chain reaction. All CD19(+) B lymphocytes expressed TNFRSF13C by flow cytometry, but the mean fluorescence intensity (MFI) was decreased in patients with active disease compared to patients in remission and healthy controls, while no significant difference of TNFRSF13C mRNA was found between ITP patients and controls. The mRNA and plasma TNFSF13B were elevated in active ITP patients, and TNFRSF13C MFI level was inversely correlated with plasma TNFSF13B in active patients. In vitro assays showed that TNFRSF13C MFI was decreased after long exposure to TNFSF13B. No significant difference for TNFRSF13B or TNFRSF17 was found between ITP patients and controls. In conclusion, TNFRSF13C expression is reduced on CD19(+) cells in active ITP patients. This down-regulation occurs through a post-transcriptional mechanism and could be a consequence of chronic increase of TNFSF13B.