Recapitulation of posttransfusion purpura by cross-strain platelet immunization in mice

Abstract

Posttransfusion purpura (PTP) is an uncommon but life-threatening condition characterized by profound thrombocytopenia occurring ∼1 week after a blood transfusion. The hallmark of PTP is a potent immunoglobulin G antibody specific for a transfused platelet-specific alloantigen, usually located on glycoprotein IIb/IIIa (GPIIb/IIIa; αIIb/β3 integrin). It is widely thought that this alloantibody somehow causes the thrombocytopenia, despite absence from host platelets of the alloantigen for which it is specific. In studies described here, we found that cross-strain platelet immunization in mice commonly induces GPIIb/IIIa-specific alloantibodies combined with platelet-specific autoantibodies and varying degrees of thrombocytopenia, and we identified 1 strain combination (129S1Svlm/PWKPhJ) in which 95% of immunized mice made both types of antibody and developed severe thrombocytopenia. There was a strong inverse correlation between autoantibody strength and platelet decline (P < .0001) and plasma from mice that produced autoantibodies caused thrombocytopenia when transfused to syngeneic animals, arguing that autoantibodies were the cause of thrombocytopenia. The findings define a model in which a routine alloimmune response to platelets regularly transitions to an autoimmune reaction capable of causing severe thrombocytopenia and support the hypothesis that PTP is an autoimmune disorder.

Characterization of glycoprotein IIb/IIIa‐specific alloantibodies induced by cross‐strain platelet immunization in mice

“…However, many studies have failed to consider the possibility that the immunized mice may have produced both MHC‐specific and GPIIb/IIIa‐specific alloantibodies. Findings described here and in a previous report 1 show that interstrain AA mismatches in extracellular domains of GPIIb/IIIa are common and highly immunogenic (at least in the mouse strains studied by us) and that antibodies recognizing them are capable of destroying platelets. It is important that the immunogenicity of GPIIb/IIIa and possibly other platelet‐specific GPs be considered in studies of platelet transfusion refractoriness conducted in mice.…”

“…In previous work, we showed that cross‐strain platelet immunizations between C57, 129, SPRET, and PWK mice consistently leads to production of platelet‐reactive alloantibodies that predominantly recognize GPIIb/IIIa on immunizing platelets 1 . Findings described here show that two monoclonal antibodies, one derived from a C57 to SPRET and the other from a PWK to 129 immunization, recognize single AA polymorphisms in GPIIb that differ between the immunizing and immunized strains, namely, G111 in C57 and V37 in PWK.…”

“…However, the alloantibodies may not simply be innocent bystanders. In previous reports, we have described a mechanism still under investigation suggesting that the autoantibodies evolve directly from alloantibodies in the course of random somatic hypermutation 1,12 …”

“…Ethylenediaminetetraacetic acid blood samples (Microvette; Sarstedt, Numbrecht, Germany) were collected from the submandibular vein, complete blood counts were performed with an automated animal blood counter as described previously. 1 Selected mice were sacrificed and spleens collected. Splenocytes were isolated and fused with NP-3 cells as previously described.…”

“…In recent studies, we found that interstrain platelet immunizations given intraperitoneally with adjuvant or intravenously between selected strains of inbred mice routinely lead to production of alloantibodies that recognize immunizing but not autologous platelets. 1 With certain strain combinations, intraperitoneal (IP) immunizations also induced platelet-reactive autoantibodies and severe thrombocytopenia. The mouse model resembles the human disorder posttransfusion purpura (PTP), in which profound, often lifethreatening thrombocytopenia develops in conjunction with the alloimmune response against a transfused human platelet alloantigen (HPA), usually HPA-1a, defined by a proline to leucine substitution at position 33 of platelet glycoprotein (GP) IIIa.…”