(P-CB-24) Regulation of RBC Alloantibody Responses by Interferon Gamma (IFNγ)

Background/Case Studies:

Background: Exposure to non-ABO antigens during red blood cell (RBC) transfusion can induce anti-RBC antibodies that promote hemolytic events. Two-thirds of patients with systemic lupus erythematosus (SLE) express a type 1 interferon (IFNα/β) gene signature associated with disease severity. SLE patients also have an increased frequency of RBC alloimmunization. Although the underlying mechanisms are not well understood. It was recently reported that IFNα/β induce RBC alloimmunization in an IFNα/β-dependent lupus mouse model but are unable to promote alloimmunization in an IFNα/β-independent genetic mouse model of lupus (MRL/lpr). Studies indicate that type 2 interferons (IFNγ) are elevated in patients with SLE and MRL/lpr mice. However, the role of IFNγ in RBC alloimmunization and its potential link to unresponsiveness towards RBC alloimmunization has not been investigated. The present study aims to understand the relationship between IFNγ-mediated inflammation and RBC alloimmunization unresponsiveness by utilizing the IFNα/β-independent (MRL/lpr) lupus model.

Study

Design/Methods:

Methods: To examine RBC alloimmunization, female wild-type (WT) and MRL/lpr mice were first treated with and without antibodies blocking the IFNγ receptor (anti-IFNγR1) twice/week for three weeks, and then treated with and without poly(I:C), a proinflammatory viral mimetic, for 3hrs before transfusion with RBCs that express the human KEL glycoprotein (KEL RBCs). Anti-KEL IgG antibodies were measured 7-21 days after transfusion by flow cytometric crossmatch. Serum interferon-stimulated genes (ISGs) were examined in wild-type (WT) and MRL/lpr mice, treated with or without poly(I:C). Anti-dsDNA autoantibodies were examined in MRL/lpr mice with and without anti-IFNγR1 treatment. To determine the statistical significance between three or more groups Kruskal-Wallis with a Dun’s post-test was used (*p< 0.05).

Results/Findings:

Results: MRL/lpr mice treated with anti-IFNγR1 and poly(I:C) were able to produce anti-KEL IgG antibodies, compared to poly(I:C) treated or untreated MRL/lpr mice. ISGs were elevated in poly(I:C)-treated mice, but not in untreated WT or MRL/lpr mice (Figure 1a). Anti-IFNγR1 treatment to MRL/lpr mice did not affect anti-dsDNA IgG antibodies (Figure 1b), an indicator of lupus-like phenotype.

Conclusions:

Conclusion: Transfusion of KEL RBCs induces alloimmunization in an IFNα/β-dependent lupus model, but not in an IFNα/β-independent model. Lupus-like phenotype of MRL/lpr is not sufficient to induce alloimmunization. Type 2 interferon (IFNγ) signatures may be responsible for suppressed inflammation-induced RBC alloantibody responses in some lupus models. Collectively, these findings warrant investigation of the role of IFNγ in RBC alloimmunization in patients with SLE.