No abstract

Idiopathic hypereosinophilic syndrome (HES) characterized by unexplained and persistent hypereosinophilia is heterogeneous and comprises several entities: a myeloproliferative form where myeloid lineages are involved with the interstitial chromosome 4q12 deletion leading to fusion between FIP1L1 and PDGFRA genes, the latter acquiring increased tyrosine kinase activity. And a lymphocytic variant, where hypereosinophilia is secondary to a primitive T lymphoid disorder demonstrated by the presence of a circulating T-cell clone. We performed molecular characterization of HES in 35 patients with normal karyotype by conventional cytogenetic analysis. TCRc gene rearrangements suggesting T clonality were seen in 11 (31%) patients, and FIP1L1-PDGFRA by RT-PCR in six (17%) of 35 patients, who showed no evidence of T-cell clonality. An elevated serum tryptase level was observed in FIP1L1-PDGFRA-positive patients responding to imatinib, whereas serum IL-5 levels were not elevated in T-cell associated hypereosinophilia. Sequencing FIP1L1-PDGFRA revealed scattered breakpoints in FIP1L1-exons (10-13), whereas breakpoints were restricted to exon 12 of PDGFRA. In the 29 patients without FIP1L1-PDGFRA, no activating mutation of PDGFRA/ PDGFRB was detected; however; one patient responded to imatinib. FISH analysis of the 4q12 deletion was concordant with FIP1L1-PDGFRA RT-PCR data. Further investigation of the nature of FIP1L1-PDGFRA affected cells will improve the classification of HES.

SununaryInterleukin 5 (IL-5), the major factor involved in eosinophil differentiation, is produced by T cells or mast cells. In the present study, we found that eosinophils infiltrating the mucosa of four patients with active coeliac disease also express the Ib5 mRNA. No positive signal was obtained in normal duodenum tissues and in the cell infiltrate from patients submitted to gluten restriction. The identification of labeled mucosal cells as eosinophils relied on their typical morphology. Moreover, highly purified blood eosinophils from three out of four patients with eosinophilia were also strongly labeled with the Ib5 antisense but not with the corresponding sense probe. Together, these results suggest that eosinophils have the capacity to synthesize IL-5, which could contribute to paracrine interactions with T and B cells and, in autocrine fashion, locally partidpate, through binding to the Ib5 receptor, to eosinophil differentiation and activation. These data might have implications not only in the pathology of coeliac disease but also in other diseases associated with eosinophil infiltration.

Considerable variations in the distribution of eosinophil populations were revealed by density gradient centrifugation of peripheral blood leukocytes from 14 normal subjects and 31 patients with a transient or persistent hypereosinophilia. Such a purification procedure enabled us to collect in healthy controls, eosinophils (77.1 ± 15.9% SD purity) with an appreciable cell recovery (21.7 ± 14.0% SD) in the densest gradients (‘normodense’ cells). A high degree of purity was obtained in the same gradients, with leukocytes from patients with hypereosinophilia (84.4 ± 11.9% SD pure eosinophils) but the cell recovery was significantly decreased (4.1 ± 3.4% SD; p < 0.001). A study of the various fractions found to contain eosinophils showed cells with an altered cellular density (‘hypodense’ cells) especially in marked hypereosinophilia. Furthermore, studies on leukocytes from patients with a very high hypereosinophilia (differential cell count > 70%) led to the recovery of almost pure fractions of eosinophils in the low density gradients. Functional studies were performed on each distinct cell fraction collected. They included investigations of their cytotoxic ability in a heterologous antibody-dependent cell-mediated cytotoxicity assay and their biochemical activity by using a previously described technique evaluating the membrane hexose transport. Variability in the functional potentialities was observed in relation to the cellular density: higher cytotoxic eosinophil abilities were noted in the case of the ‘hypodense’ cell population. According to biochemical criteria, these latter cells appear to be more activated and capable of responding to stimulation.