Brief communication‘Idiopathic’ eosinophilia with an Occult T-cell clone: Prevalence and clinical course
Introduction
From a pathogenetic standpoint, eosinophilia results either from acquisition of a somatic mutation (e.g. FIP1L1-PDGFRA in chronic eosinophilic leukemia (CEL)) that biases hematopoietic progenitor cells towards an eosinophil fate (cell-intrinsic) or as a response to exogenous cytokines (e.g. interleukin (IL)-5 and IL-4), which promote the same effect (cell-extrinsic). An example of the latter is the entity is termed “lymphoproliferative variant” of hypereosinophilic syndrome (L-HES), which is a poorly understood T-cell clonal disorder with predominant skin involvement [1], [2], [3]. The T-cell clone (Th2 phenotype), which is the source of eosinophilopoietic cytokines, is frequently occult in this setting, and is identified on the basis of an abnormal immunophenotype and/or by clonal rearrangements of the T-cell receptor (TCR). It has been recently suggested that the FIP1L1-PDGFRA mutation alone may not be sufficient to induce a CEL-like disease, but may require cooperation with increased IL-5 levels to induce this phenotype [4]. We present here the prevalence, clinical characteristics, and FIP1L1-PDGFRA status of L-HES patients seen at our institution.
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Methods
Consecutive patients with eosinophilia were identified by querying our institutional electronic database from 1995 to 2004, and clinical data was extracted after Institutional Review Board approval. Clonal rearrangements of the γ chain of the TCR were identified by polymerase chain reaction (PCR) followed by capillary gel electrophoresis in all cases, and confirmed by Southern Blot analysis of the TCR β gene, using standard methods in our clinical pathology laboratory [5]. The fluorescence in
Results and discussion
Our screen identified 205 consecutive patients with eosinophilia (absolute eosinophil count [AEC] > 600/μL), who also had a bone marrow study done at our institution. We used a lower AEC cutoff (relative to hypereosinophilic syndrome [HES] criteria) in the initial screen given that many patients seen in our predominantly referral practice are already on some form of therapy (commonly corticosteroids) at the time of their initial presentation to us. Of the 205 patients, 99 patients underwent
Acknowledgements
Contributions. AP and AT wrote the paper. CV, AP, JB, SV, HK, and AT participated in study design, and/or abstracted clinical data and analyzed the data. RK performed and interpreted the cytogenetic analysis.
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