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

Objectives: 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. Methods: 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. Results: 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 (P < 0.0001), a higher white-blood-cell count (P = 0.006) and a higher erythrocyte sedimentation rate (P = 0.003) at the time of diagnosis. Conclusions: 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.