Induction of ImmuneThrombocytopenia in Mice Expressing Human Fcy Receptors: An Improved Experimental Model that Better Reflects the Inflammatory State Associated with ITP

Abstract

Background: Fcγ receptors (FcγRs, e.g. FcγRIIa) contribute to the pathophysiology of immune thrombocytopenia (ITP). Mouse models are often used to study the biology of ITP. In these, thrombocytopenia is achieved by passive administration of anti-platelet antibodies. However, they fail to reflect the inflammatory state associated with human ITP. Differences in the types and ex-pression patterns of FcγRs between humans and mice may contribute to this discrepancy. Aims: Here, using mice transgenic for human FcγRs, we assessed ITP induced by native or chimeric anti-mouse platelet antibodies. Methods: Mice transgenic for either the entire human Fcγ-receptorfamily (huFcγR) or only FcγRIIa (hFc), and wild type (WT) mice, were injected i.v with anti-mouse platelet antibodies: MWReg30, 6A6 or chimeric 6A6 (c6A6), containing rat, mouse or human Fc domains, respectively. Core temperature and platelet counts were measured before and 30 min after injection. Alternatively, MWReg30 and c6A6were injected i.p and platelets counted daily for 7 days. Plasma IFN-γ,TNF-α, IL-2, IL-6 and IL-10 were measured 30 min after i.v, and on days0, 3, 5 and 7 after i.p injections. Results: MWReg30 injected i.v induced severe thrombocytopenia(>90% platelet loss), hypothermia, and shock in huFcγR and hFc but not WT mice. 6A6 caused severe thrombocytopenia in huFcγR and hFc but hypothermia and shock only in huFcγR. In contrast, c6A6caused mild thrombocytopenia (30% platelet loss) without hypothermia or shock in all strains. Severe sustained thrombocytopenia was achieved in all strains injected i.p. Significant elevation of IFN-γ, TNF-α, IL-6 and IL-10 levels was observed in huFcγR mice injected i.v or i.p. with MWReg30, and in both huFcγR and hFc mice with c6A6, but not in WT mice. Conclusions: The use of anti-platelet antibodies having a human effector region in mice expressing human FcyRs is an improved model that more closely reflects the pathophysiology of human ITP and reveals its inflammatory nature.