title: Hydroxyurea and Zileuton Differentially Modulate Cell Proliferation and Interleukin-2 Secretion by Murine Spleen Cells: Possible Implication on the Immune Function and Risk of Pain Crisis in Patients with Sickle Cell Disease.
abstract: BACKGROUND
  Hydroxyurea (HU) reduces major complications associated with sickle cell disease in part because of the induction of fetal hemoglobin. However, because of its antiproliferative property, its long-term use may impair immunity. Zileuton, a derivative of HU, also induces fetal hemoglobin and has antiinflammatory properties, a feature that can reduce the risk of sickling. Our goal was to investigate the capacity of both drugs to modulate the secretion of interleukin-2 (IL-2), a regulatory cytokine for immune responses.
  
  
  METHODS
  Spleen cells obtained from 11 4-month-old C57BL/6 female mice were incubated without and with 10 μg/mL HU or zileuton, 2.5 μg/mL concanavalin A (ConA), 20 μg/mL phytohemagglutinin (PHA), and 50 ng/mL anti-CD3 antibody for 12-48 h. IL-2 was measured in the supernatant by enzyme-linked immunosorbent assay and cell proliferation by (3)H-thymidine uptake.
  
  
  RESULTS
  While HU reduced lymphocyte proliferation in response to mitogens (P<0.05), zileuton did not. Baseline IL-2 concentration and PHA-induced IL-2 were not significantly affected by either drug. Contrary to what we expected, while HU increased IL-2 supernatant levels 1.17-fold to 6.5-fold in anti-CD3 antibody-treated cells (P<0.05), zileuton decreased them 35%-65% (P<0.05). Zileuton likely reduced IL-2 levels by inhibiting 5-lipoxygenase, hence leukotriene B4 production, an IL-2 inducer. HU did not decrease IL-2 secretion likely because of its lack of effect on mRNA and protein synthesis.
  
  
  CONCLUSIONS
  Modulation of IL-2 secretion by zileuton and/or reduced lymphocyte proliferation by HU may impair the immune response of patients with sickle cell disease but may also be beneficial by attenuating inflammation independently of fetal hemoglobin induction.
authors.affiliation: Department of Pediatrics, Louisiana State University Health Sciences Center, New Orleans, LA ; Division of Research, The Research Institute for Children, Children's Hospital, New Orleans, LA.
authors.forename: Solo
authors.initials: S
authors.lastname: Kuvibidila
authors.affiliation: Department of Pediatrics, Division of Hematology/Oncology, Louisiana State University Health Sciences Center, New Orleans, LA ; Department of Pediatric Hematology/Oncology, Ochsner Clinic Foundation, New Orleans, LA ; The University of Queensland School of Medicine, Ochsner Clinical School, New Orleans, LA.
authors.forename: Rajasekharan P
authors.initials: RP
authors.lastname: Warrier
authors.affiliation: Department of Pediatrics and The Sickle Cell Center, University of South Alabama College of Medicine, Mobile, AL.
authors.forename: Johnson
authors.initials: J
authors.lastname: Haynes
authors.affiliation: Department of Pediatrics and The Sickle Cell Center, University of South Alabama College of Medicine, Mobile, AL.
authors.forename: Surendra B
authors.initials: SB
authors.lastname: Baliga
keywords: Anemia–sickle cell; hydroxyurea; interleukin-2; mice; zileuton