Following the historical findings cited above, studies identified the cytokine, interleukin 5 (IL5), as the eosinophil growth-stimulating CFU made by T cells from patients suffering the idiopathic hypereosinophilic syndrome. Subsequent studies likewise identified IL5 as a cytokine being overproduced by certain<unk> s taken from patients with<unk><unk>  eosinophilia. These and other studies support the view that<unk>  is a unique disease characterized by hypereosinophilia secondary to the pathological production of eosinophil growth factors, particularly IL5 but possibly also IL4; IL13, and GM-CSF by one or more aberrant clones of T cells. The aberrant T cell clone, as defined by immunophenotyping their expression of certain cell surface molecules, the cluster of differentiation (i.e. CD) proteins, varies from patient to patient; furthermore, some of these clones also exhibit clonal rearrangements in their T-cell receptor gene. The most common immunophenotypes in<unk><unk>  eosinophilia are: a) CD3(−), CD4(+) T cells, b) CD3(+), CD4+, CD8(−) T cells, c) CD3(+), CD4(+), CD7(−) T cells also bearing αβ+ T cell receptors, d) CD3(+), CD4(+), CD7(-) T cells, and e) CD3(+), CD4(+), CD2(-) T cells. Chromosome abnormalities such as breakage of the long ("q") arm of chromosome 16, partial deletions in the q arm of chromosome 6 or short ("p") arm of chromosome 10, and trisomy of chromosome 7 are occasionally detected in these T cells. Regardless of immunophenotype, these T cells typically express CD45RO plus HLA-DR and/or IL2RA (also termed CD25} cell surface antigens. Expression of these antigens is characteristic of activated memory T cells. The underlying cause(s) for the origination and expansion of the phenotypically and clonally aberrant T cells in<unk>  remains unclear. In all events, these aberrant T cells are not, at least initially, malignant although they do exhibit pathological behavior. They produce, in addition to interleukin 5, another eosinophil-stimulating cytokine, Granulocyte macrophage colony-stimulating factor. The aberrant T cells also produce: IL4, a T cell-stimulating cytokine; interleukin 13, a cytokine mediator of allergic reactions, particularly those occurring in the lung; IL2, a t cell-stimulating cytokine, tumor necrosis factor alpha, a proinflammatory cytokine that regulates immune responses, and, at least in the aberrant T cells of certain patients, Interferon gamma (i.e. IFGγ), s cytokine that regulates innate and adaptive immunity. These cells also stimulate other, non-clonal<unk> s to secrete chemokine (C-C motif) ligand 17 (also termed CC17 or TARC), a T cell-stimulating cytokine belonging to the CC chemokine family. While IL-5 is regarded as the principal mediator of the eosinophilia found in<unk> , one or more of the other cited cytokines may also contribute to this eosinophilia as well as other pathological features of the disease.
Lymphocyte-variant hypereosinophilia
Tropical eosinophilia
Drug reaction with eosinophilia and systemic symptoms
Clonal hypereosinophilia
Diffuse infiltrative lymphocytosis syndrome
Familial eosinophilia
Hypereosinophilic syndrome
IgA vasculitis