The objective of this controlled pilot study was to determine if mRNA coding for interleukin‐5 (IL‐5), a cytokine that promotes eosinophil differentiation, growth, and migration, could be detected in three T‐cell lymphomas that were infiltrated extensively by eosinophils. To detect mRNA coding for IL‐5, we performed an RNA polymerase chain reaction on mRNA extracted from three T‐cell lymphomas with eosinophilia and from 29 positive and negative validation controls. Using this procedure, we detected a 293‐base pair, IL‐5‐specific amplification product in the three cases of T‐cell lymphoma with eosinophilia and in 11 of 12 positive validation controls, including 10 cases of Hodgkin's disease with eosinophilia. IL‐5 mRNA was not detectable in the 17 negative validation controls. This preliminary study suggests that IL‐5 mRNA is detectable by polymerase chain reaction in three cases of T‐cell lymphoma with eosinophilia. © 1993 Wiley‐Liss, Inc.
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