We show by mRNA hybridization analysis and immunostaining using a mouse monoclonal antibody (moAb) to recombinant human interleukin 9 (IL-9) that both primary and cultured Hodgkin and Reed-Sternberg (H-RS) cells produce IL-9 transcripts and protein and express surface binding sites for IL-9. In addition, the growth of H-RS cells obtained from the HDLM-2 line (abundantly producing IL-9 transcripts) was significantly inhibited when anti-IL-9 moAb or an IL-9 antisense oligodeoxyribonucleotide was added to cultures. Excess addition of recombinant human IL-9 relieved the effects of anti-IL-9 moAb on HDLM-2 growth. Growth of H-RS cells of the KM-H2 line, which displays only low amounts of IL-9 detectable upon hybridization of polyadenylic acid-selected RNA only, was not affected by anti-IL-9 moAb. The proliferative capacity of KM-H2 cells in soft agar and liquid suspension cultures was, however, augmented at least 3-fold when cells were exposed to recombinent human IL-9. In conclusion, our results show that IL-9 is expressed by H-RS cells and point to a possible role of this molecule as a growth factor for these cells.

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Supported by the Mildred Scheel Stiftung für Krebsforschung (M. A. B., F. H.).

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