Recent observational cohort studies indicated that the incidence of connective tissue diseases such as systemic lupus erythematous (SLE), in adult patients with sickle cell disease (SCD), appears to be increasing. The exact causes underlying this increased risk are still unknown, but patients with SCD are at risk of infections due to immune dysfunction, and a link with regulatory B (Breg) cells is possible as these cells suppress inflammatory responses, maintain tolerance and prevent the development of SLE in animal models via the production of interleukin-10 (IL-10). Herein, we numerically and functionally evaluated Breg cells in a well-defined group of SCD patients. The classification for SCD was based on patients' history, clinical examination, hematological and radiological findings. The American College of Rheumatology (ACR) criteria were used to classify and diagnose SLE patients with or without SCD. Patients were stratified into three groups including SCD patients with SLE (n=21), patients with SCD only (n=24) and patients with SLE only (n=24). Normal healthy individuals (n=24) were used as controls. Circulating levels of Breg cells were prospectively assessed by immuno-phenotyping using specific surface markers, CD19, CD24 and CD38 by flow cytometry. The functional properties were evaluated by IL-10 production and STAT3 phosphorylation after stimulation and cell culture. Unstained cells and n-1 monoclonal antibodies along with live and dead stain were used as controls in all experiments. Comparisons among study groups were performed using ANOVA and unpaired t test, while the Spearman's correlation was used to assess associations. The demographic data were similar among the study groups. All participants were free of infections such as human immunodeficiency virus, hepatitis B and C virus and syphilis. SCD patients with SLE and patients with SLE only were positive for autoimmune markers and showed an average ACR score of five and six respectively. The frequency of Breg cells, as phenotypically defined as CD19+CD24hiCD38hi, ranged between 1.5-8% in healthy controls. The circulating levels of Breg cells were significantly reduced in SCD patients with or without SLE and patients with SLE only when compared to the healthy controls (p<0.0001). Similarly, compared to healthy controls, Breg cells from SCD patients with or without SLE and patients with SLE only produced significantly lower amount of IL-10 (p<0.0001). Likewise, STAT3 phosphorylation was also decreased in Breg cells from SCD patients with or without SLE and patients with SLE only compared to the healthy controls (p<0.0001). Demographic and hematological data along with the treatments such as hydroxyurea and hydroxychloroquine did not affect the levels and functions of Breg cells. Moreover, most of the associations among study variables did not reach a statistical significance, except a moderate negative correlation was evidenced between total white blood cells (x109/L) and Breg cells (ρ=-0.41, p=0.04) in SCD patient group. Collectively, these findings showed numerical and functional deficits of Breg cells in SCD patients with or without SLE and patients with SLE only. This may suggest that Breg cell capacity to maintain tolerance and control inflammation is imbalanced in SCD patients, thereby favoring the development of SLE. Disclosures No relevant conflicts of interest to declare.
Although patients homozygous for the sickle cell disease (SCD) mutation have an identical genotype, the severity of the disease can be extremely variable. The hemoglobin (Hb) S mutation has been associated with five different beta S-globin gene cluster haplotypes (βS-haplotypes) that show different clinical expression. Because genetic modifiers can modulate treatment response, we hypothesized that βS-haplotypes can affect levels of invariant natural killer T (iNKT) cells, which are known to play a key role in the pathogenesis of SCD, and are being considered as a potential target to treat acute crises in SCD patients. Herein we evaluated the impact of βS-haplotypes and HbF concentration on iNKT cell and dendritic cell (DC) subsets in a well-defined group of patients with SCD in a steady state. Sickle cell anemia patients were selected based on the history of patients, clinical examination and hematological findings. The βS-haplotypes were identified by polymerase chain reaction-restriction fragment length polymorphism analysis for seven restriction sites. The iNKT cell subsets were characterized by the positive-staining of Vα24Jα18 T cell receptor alpha chain, along with CD3, CD4 and CD8 surface markers and the intra-cellular cytokine production of interferon-gamma (Th1-like), interleukin-4 (Th2-like) and interleukin-17 (Th17-like) cells using flow cytometry and cell culture. The myeloid DC (mDC) and plasmacytoid DC (pDC) cells were identified by the expression of HLA-DR, CD123, CD11c, Lin and CD1d, a non-classical molecule that induces the activation of iNKT cells by flow cytometry. Comparisons among βS-haplotypes were performed using ANOVA and unpaired t test, while the Spearman's correlation was used to assess associations. Among the 125 sickle cell anemia patients studied, Benin haplotype (40%) was the most common followed by Bantu (21%), Arab/Indian (18%), Atypical (12%) and Benin/Bantu or Benin/Arab-Indian or Bantu/Arab-Indian (9%). The majority of subjects with Benin/Benin βS-haplotype had a severe to moderate clinical profile similar to Bantu/Bantu or Arab/Indian βS-haplotype groups (P=0.23). A trend toward increased levels of CD3iNKT, CD4iNKT and CD8iNKT cell subsets was observed in the subjects with the Benin/Benin βS-haplotype, when compared to other βS-haplotype groups (P=0.06). Interestingly, subjects with the Benin/Benin βS-haplotype exhibited slightly higher levels of Th1-like cells, but not Th2-like and Th17-like cells, when compared to subjects with the Bantu/Bantu or Arab/Indian βS-haplotype groups (P=0.047). Comparisons between the levels of mDC and pDC cell subsets, as well as the expression of CD1d on these DC cells, showed no statistically significant differences among the βS-haplotype groups (P=0.42). Similarly, levels of iNKT cell subsets, Th1-like, Th2-like, and Th17-like cells as well as DC subsets were similar among patients who received or not hydroxyurea therapy, independently of βS-haplotype groups (P= 0.09). Likewise, coexistence of high HbF and βS-haplotypes did not show any significant association with iNKT cell subsets. Collectively, our findings suggest that neither the βS-haplotypes or HbF levels nor the hydroxyurea therapy or clinical severity appeared to be associated with iNKT cell or DC cell subsets in patients with SCD. The effects of other genetic modifiers such as alpha/beta-thalassemia and G6PD deficiency on iNKT cell subsets need to be evaluated in future studies. Disclosures No relevant conflicts of interest to declare.
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