[T cell repertoires correlate with pathogenesis of chronic idiopathic thrombocytopenic purpura]

Abstract

Objective: To determine the T lymphocytic clones that correlate with the pathogenesis of idiopathic thrombocytopenic purpura (ITP) by investigating complementarity determining region (CDR3) repertoires of T cell receptors (TCRs) beta chain variable region (BV).

Methods: Twenty-five patients with idiopathic thrombocytopenic purpura (including 15 patients with acute ITP and 10 patients with chronic ITP), twenty normal peoples and 20 normal umbilical cord blood samples were enrolled. Reverse transcription-polymerase chain reaction (RT-PCR) was used to amplify 24 subfamily genes of the TCR (BV from the peripheral blood lymphocytes (PBLs) of the ITP patients and normal controls, the implications underwent electrophoresis on denatured polyacrylamide sequencing gel, establishing a map of TCR BV CDR3 gene expressing repertoire. The bands that widened or disappeared of the TCR BV gene repertoire on the electrophoresis gel were used to analyze the variety of T cell clones in the cases of ITP. Comparing the sequences of TCR BV CDR3 gene repertoire in normal and abnormal T cell clones made it possible to understand the relationship between TCR BV gene and ITP.

Results: (1) In aITP, TCR BV CDR3 size distribution was similar to that of the normal controls and oligoclonality could be observed in 15 cases with an average value of 2.7 +/- 0.9 per person. Abnormal TCR BV CDR3 size distribution in aITP had little difference compared with that in the healthy controls (P = 0.179). There was no common expanded T cell clones in aITP, while abnormal TCR BV CDR3 distribution could be observed significantly different between the cITP patients and healthy controls (P < 0.05), with oligoclonality at an average value of 7 +/- 3 per person in 10 cases. Common clonal T cell expansions could be observed in BV8, BV13.1, BV14 and BV17 subfamilies. In 10 cITP patients, sequence could be read from 18 out of 20 dense and strong T cell clone bands on the map of TCR BV CDR3, which suggested that a dominant monoclonal T cell expanded in cITP. (2) Different patients shared a common or similar CDR3 encoded by the TCR BV gene of the expanded T cell clones. The same CDR3 was found in 2/4 expanded BV 17 T cell clones, with only 2 amino acids different in framework four (FR4). Two T cell clones had almost the same sequence of CDR3 of BV17 except for only four basepair differences in their full sequences. The full TCRBV gene sequences remained the same in 2 T cell clones for TCRBV8 and in other 2 T cell clones for TCRBV13.1 in cITP group. It showed that an expanded T cell clones with common function existed and could recognize common antigen in the body of patients with cITP. In analyzing the common motif in CDR3 of different cITP, three common motifs were found: GANVLTFGAG, E/DTQYFGPG and N (K) EQFFGPG, which were separately used in different TCRBVCDR3 of 18 expanded T cell clones. Among these motifs, TCRBV17 of 3 T cell clones had common GANVLTFGAG; TCRBV of 4 T cell clones had common N (K) EQFFGPG; and TCRBV of 7 T cell clones had common E/DTQYFGPG.

Conclusion: aITP has no significant T cell clones expanded, while cITP usually demonstrates some expanded abnormal oligoclones which may correlate with the pathogenesis of cITP. cITP patients share 3 common motifs for TCRBV CDR3, which is possibly related to recolonization of the similar autoantigens.