Reduction in serum IL‐10 levels is a surrogate marker for predicting vaso‐occlusive crisis in sickle cell disease
Authors: Sameh Sarray, Najat Mahdi, Layal R. Saleh, Wassim Y. Almaoui
Journal: American Journal of Hematology (2014)

To the Editor: Altered inflammatory cytokine expression substantially impacts the development of sickle cell disease (SCD) vaso-occlusive crises (VOC) 1, 2. This was evidenced by the elevation in proinflammatory, and the reduction in anti-inflammatory cytokine levels in SCD patients compared to healthy individuals 1, 2. The anti-inflammatory cytokine interleukin-10 (IL-10) was described to mediate several SCD-associated events, and reduction in its expression was reported in unselected SCD patients compared to healthy subjects 3, and in SCD patients with VOC compared to VOC-free SCD patients 1, 4. Other studies reported contradictory findings on the contribution of IL-10 to SCD and its complications 5, 6, which was likely attributed to the low number of subjects and selection criteria used in those studies. The present study examined the relationship between reduced IL-10 levels and the occurrence of VOC and VOC-related parameters in pediatric SCD patients. Study subjects comprised 148 SCD patients with VOC event (VOC Group) and 63 asymptomatic control SCD patients who reported no VOC events for the past 9 months (Steady-state Group). SCD diagnosis was according to hemoglobin profile. VOC was defined as acute events characterized by diffuse pain in different body sites related only to SCD. VOC management consisted mostly of nonsteroidal anti-inflammatory drugs (NSAID; 67.7%), along with narcotics (2.2%), and narcotics plus NSAID (20.7%). Comparable frequencies of hydroxyurea- (P = 0.80) and folic acid- (P = 0.32) treated patients were seen in both patient groups. Steady-state controls were matched with VOC patients according to gender, HbS and HbF profiles, and other hematological indices. Local research and ethics committees approved the study protocol, which was in agreement with the 2000 Helsinki declaration. Serum samples were tested for IL-10 using human IL-10 sandwich ELISA (R&D Systems, Minneapolis, MN). Assay sensitivity was 3.9 pg/ml, and interassay and intra-assay precision (coefficient of variation%) ranged from 5.9 to 7.5% and 1.7 to 5.0%, respectively. Quantitative data are described as medians, and upper and lower quartiles. The differences between VOC cases and SCD control groups were determined by Mann–Whitney comparison by ranks, since IL-10 values showed a nonparametric distribution. Using SCD controls as the reference group, univariate followed by multivariate logistic regression analyses were performed to analyze IL-10 as risk factor for VOC; IL-10 levels were used as continuous, and then as categorized variables. Correlations among continuous variables were determined by Spearman correlation coefficient (r). Gender distribution and age at examination were comparable between VOC and steady-state SCD patients. Hematological and inflammatory indices, including HbS, HbF. total hemoglobin, hematocrit, while blood cell count, platelet count, Mean corpuscular volume, Mean Corpuscular Hemoglobin, mean corpuscular hemoglobin concentration, and reticulocyte counts were comparable between both SCD patients groups. VOC patients reported 4.6 ± 2.2 episodes/year (mean duration: 4.6 ± 2.5 days/episode). Most (84.0%) VOC cases required hospital admission to manage the painful crisis; the pain score being 7.1 ± 1.8 (on 0–10 scale). At baseline examination, IL-10 levels were reduced in VOC cases than in control patients (P < 0.001). IL-10 levels were categorized into four quartiles according to IL-10 values in healthy control group. There was enrichment of low IL-10 producers (first quartile) in VOC group (P < 0.001), and increased prevalence of high IL-10 producers (fourth quartile) in the steady-state SCD control group (P < 0.001). Given the shift in IL-10 values between VOC cases and steady-state controls, where significant VOC associations were seen in low IL-10 values, we performed receiver operation characteristic (ROC) analysis to determine the power of IL-10 values to predict VOC (Fig. 1). The area under the curve of IL-10 values was 0.688 (P = 8.7 × 10−6; 95% CI: 0.617–0.760). Reduced IL-10 levels correlated with VOC frequency (episodes/year; r = −0.199; P = 0.008), VOC type (localized vs. generalized; r = −0.254; P = 0.001), and pain scale (r = −0.164; P = 0.028), but not with HbS (P = 0.451) and HbF (P = 0.649) levels, or other VOC parameters (age at VOC onset, hospitalization, VOC treatment regimen). A significant association between reduced IL-10 levels and VOC pathogenesis was evidenced by enrichment of low IL-10 producers in the VOC group, and the strong correlation between reduced IL-10 secretion and VOC parameters, namely severity, frequency, and VOC type. This demonstrates that IL-10 values have good predictive power for VOC occurrence. Some limitations to these findings are noteworthy. IL-10 levels were measured following VOC, which question the cause–effect relationship, and in including only pediatric cases, thus necessitating parallel studies on adult SCD patients. Despite these shortcomings, our results support the notion of covert inflammatory response in VOC. Sameh Sarray1, Najat Mahdi2, Layal R. Saleh1, Wassim Y. Almaoui1* 1Department of Medical Biochemistry, Arabian Gulf University, Manama, Bahrain 2Department of Pediatrics, Salmaniya Medical Complex, Manama, Bahrain