Interleukin-27 and interleukin-37 are elevated in sickle cell anemia patients and inhibit in vitro secretion of interleukin-8 in neutrophils and monocytes

Background and objective: Inflammation is implicated in the pathogenesis of most complications seen in sickle cell anemia (SCA) patients. We aimed to evaluate serum levels of two newly discovered anti-inflammatory cytokines (IL-27 and IL-37), and pro-inflammatory cytokines among Brazilian SCA patients that are not on hydroxyurea therapy (HbSS), compared with hydroxyurea-treated patients (HbSSHU) and healthy controls (HbAA). Furthermore, we demonstrated the effect of IL-27, IL-37, and heme on in vitro secretions of IL-8 in human neutrophils and monocytes. Methods: A cross-sectional study of 82 consenting SCA (35 HbSS and 47 HbSSHU) patients in steady state and 49 HbAA consenting individuals. Clinical details were obtained from interviews and medical records. Serum levels of IL-27, IL-37, TGF-beta, TNF-alpha, IL-1 beta, IL-6, and IL-8 were quantified by enzyme linked immunosorbent assay (ELISA). Neutrophils and monocytes were isolated from healthy controls, and cultured separately with or without cytokines (IL-27 and IL-37) and heme. Supernatant IL-8 concentration was determined by ELISA. Results: Serum levels of IL-27, IL-37, IL-1 beta, IL-6, and IL-8 were significantly elevated in HbSS patients compared to HbAA controls. Serum IL-8 levels were significantly higher in HbSS and HbSSHU patients than in controls. IL-27 and IL-37 were positively correlated in both HbSS and HbSSHU patients. In vitro IL-8 production by IL-27 and IL-37 pre-treated neutrophils and monocytes was significantly inhibited even after heme addition. Conclusions: Our findings show that IL-27 and IL-37, as well as the pro-inflammatory cytokines, are elevated in HbSS patients compared with controls, suggesting that the secretion of these anti-inflammatory cytokines is driven by the presence of pro-inflammatory cytokines. This role is probably sufficient in preventing further cellular or tissue damage but not potent enough to prevent inflammation. Therefore, IL-27 and IL-37 may be potential immuno-targets for ameliorating complications associated with elevated heme levels seen in SCA and other hemolytic anemias.