IL-9 expression contributes to the cellular composition in Hodgkin lymphoma

The presence of numerous mast cells or eosinophils in Hodgkin lymphoma (HL) tumours have both been described as negative prognostic factors. One cytokine related to HL is interleukin-9 (IL-9) and it is known to affect both mast cells and eosinophils. The aim of this study was to explore if the expression of IL-9 correlates to the presence of these inflammatory cells in HL tumours.In 131 HL biopsies, immunostainings for IL-9 and IL-9 receptor (IL-9R) were performed. The same material was previously stained for mast cells and eosinophils. These data were correlated to clinical and survival data from all patients.Fifty-three percent of cases were positive for IL-9 and 19% were positive for IL-9R in the cytoplasm of the tumour cells. The IL-9 positive patients had more eosinophils (P = 0.002) and mast cells (P = 0.02) in their tumours, more often a nodular sclerosis histology (P0.0001), a higher white-blood-cell count (P = 0.006) and a higher erythrocyte sedimentation rate (P = 0.003) at the time of diagnosis.IL-9 expression is related to the histology, clinical picture and the presence of eosinophils and mast cells in HL. These results indicate that IL-9 is an important part of the cytokine network and inflammatory infiltrate in HL.