AbstractBackgroundMycosis fungoides (MF) skin lesions are characterized by low‐grade inflammation, which may be sustained by proinflammatory cytokines as probably interleukin‐33 (IL‐33). We compared serum concentrations of IL‐33 and its receptor ST2 and the frequency of selected IL‐33 single nucleotide polymorphisms (SNPs) between patients with MF and healthy controls.MethodsIn 88 patients with MF and 66 healthy controls, we analyzed SNPs in the 9894 and 11877 loci of theIL‐33gene. Moreover, we measured serum concentrations of IL‐33 and its receptor ST2.ResultsThere were no statistically significant differences in the frequencies of both IL‐33 SNPs between patients and controls. Compared with controls, patients with MF had similar IL‐33 serum concentrations (P = 0.71) but significantly increased ST2 concentrations (P < 0.001). Patients in MF‐IA stage had significantly lower ST2 serum concentrations than those with the remaining MF stages (P = 0.002). The studied variables were not related to pruritus severity. Patients with the C(+) IL‐33 11877 SNP had lower ST2 serum concentrations than patients with the C(−) 11877 SNP (P = 0.043).ConclusionsIt was published before that the knockout of theST2gene after injection of IL‐33 is associated with a reduced inflammatory reaction in the skin, as well as that IL‐33 plays a role in allergic and neoplastic disorders. Concerning the difference in ST2 concentration between control and MF group, and C IL‐33 11877 SNP possibly influencing the ST2 concentration, the role of IL‐33/ST2 signaling, needs further studies.