Cell clonality in hypereosinophilic syndrome: what pathogenetic role?

OBJECTIVE

Idiopathic hypereosinophilic syndrome (HES) is a heterogeneous disorder, including either a myeloproliferative or a lymphoproliferative variant (l-HES). In l-HES, T-lymphocytes could be involved in the pathogenesis through several cytokines, including IL5.

METHODS

We assayed both TCR Beta- and delta-rearrangements by fluorescent PCR, characterizing 14 patients affected by HES. Lyn activation (a src-kinase involved in the IL5 pathway) was also tested in 6 cases.

RESULTS

FIP1L1-PDGFRa was detected in 4 cases (28.6%); a clonal TCR was found in 10 cases (71.4%), including cases FIP1L1-PDGFRalpha-positive; four cases did not show any molecular marker. In this series, levels of IL5, IL4, IL2 and gammaIFN were measured, without any significant difference among different subgroups. All pathological samples tested did not show Lyn activation. Immunophenotype was also characterized: only one case showed an atypical CD3-/CD4+ population in the bone marrow.

CONCLUSION

This study would suggest that a real distinction between m- and l-HES is not wholly convincing and that clonal T-cell expansion could not be the "primum movens" but an epiphenomenon in HES.