Background
RBC alloimmunization is a clinically significant issue in transfusion medicine; patients with sickle cell disease have an increased risk of alloantibody production (30-50% of SS patients) compared to that of other hospitalized patients (3-10%). However, mechanisms underlying the increased frequency of alloimmunization in sickle cell patients are poorly understood.
In previous studies, inflammation in the recipient has been shown to promote alloimmunization. Transfusion models, type 1 interferons (IFNα/β) and Interferon Stimulated Genes (ISGs) have been shown to promote alloimmunization in mice. Other studies have shown that patients with inflammatory autoimmune diseases express an IFNα/β signature which may contribute to the increased frequency of alloimmunization in these populations. One recent study reported significantly elevated ISGs in neutrophils as well as evidence that IFNα is upregulated in SS patients compared to controls. Given the chronic inflammatory state in SS patients, we sought to determine the role of PBMCs and whether they also expressed an IFN gene signature that contributes to the increased frequency of alloimmunization.
Methods
The expression of the ISG, myxovirus resistance protein 1 (MxA), was measured in the blood of SS patients with more patients with SS disease (SS, n=13) and race matched healthy controls (ββ, n=3) by whole blood immunoassay (ELISA). qPCR was performed on 5 previously established ISGs to determine an IFN score, a measure of overall gene expression, from whole blood and IFNβ stimulated PBMCs of SS patients (SS, n=15) and healthy race matched controls (ββ, n=5). A LEGENDplex™ Human Anti-Virus Response Panel assay was used to determine the expression of various type 1 IFNs, cytokines and ISGs in patients with SS disease (SS, n=15) and healthy race matched controls (ββ, n=5).
Results
SS patients had significantly elevated levels of MxA (mean ± standard error of the mean, SS MxA = 12.27 ng/mL ± 15.68) compared to control patients without SS (ββ MxA = 1.52 ng/mL± 0.26, p< 0.05) (Figure 1 A) . The Legendplex showed a significant increase in IL-6, IL-10 and the ISG, IP-10. (SS IP-10= 147.81 pg/mL ± 49.24) (ββ IP-10 = 68.85 pg/mL ±10.70, p<0.01) (Figure 1 B) Analyzing the 5 ISGs, we saw a trend towards a higher IFN score in patients with SS disease than healthy controls in whole blood; this difference was significant in PBMCs stimulated with IFNB (IFN Score SS = 20.76 ± 17.18 ,ββ = 0.00 ± 3.71 , p<0.01) (Figure 1 C).
Discussion
SCD is a complex disease with many environmental and genetic factors that play roles in the severity of the disease. Any number of these factors may influence the high rates of alloimmunization found in sickle cell patients. We found increased cytokines, ISGs and IFN scores in SS patients compared to healthy controls. These findings suggest the presence of an IFNα/β gene signature in patients with sickle cell disease. Due to the relatively small sample size, we are unable to determine a correlation between alloantibodies and MxA levels or high IFN scores with this cohort. Further studies will allow us to determine if the increased interferon gene signature plays a role in the increased alloimmunization burden that these patients experience.
No relevant conflicts of interest to declare.
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