(P-CB-8) Distinct Inflammatory Signals Can Enhance Or Reduce Alloantibody Responses To Primary Platelet Transfusion And Alter Recall Responses In Mice

Background/Case Studies: Alloimmunization to platelet transfusion, which mostly targets major histocompatibility complex (MHC) antigens on platelets and leukocytes, can lead to unwanted reactions such as platelet refractoriness or transplant rejection. Patients hospitalized for severe infection can receive platelets as part of their care, and the inflammatory immune environment of the recipient could modulate the risk of platelet alloimmunization. Prior work has shown inflammation induced by polyinosinic-polycytidylic acid (poly(I:C), a viral mimetic) heightens the acute alloresponse in mice, whereas lipopolysaccharide (LPS, a gram-negative bacterial component) diminishes it. To better understand the magnitude, durability, and quality of these divergent alloresponses, this study evaluated primary and recall alloresponses over time.

Study

Design/Methods: Non-leukoreduced platelet rich plasma (PRP) from C57BL/6J donor mice was transfused into BALB/cJ recipient mice. To model underlying inflammation, some recipients were given either intraperitoneal LPS or poly(I:C) 4 hours prior to transfusion. For some, a second PRP challenge was administered at 12 weeks to examine recall. Control groups included no treatment or mice given LPS or poly(I:C) alone. Anti-donor alloantibodes were screened in serum over 24 weeks by flow cytometry. MHC tetramers were used to identify donor-reactive anti-MHC allogeneic B cells (allo-B cells) for associated cellular responses including memory and antibody-secreting B cells by flow cytometry.

Results/Findings: Transfusion alone led to strong, persistent primary alloantibody responses and rapid recall responses (p < 0.0001). Poly(I:C) enhanced acute alloantibody response to transfusion with a significant increase in IgG3 (p < 0.0258) and decrease in IgG1 (p < 0.0388) compared with transfusion alone, but plateaued to levels consistent with transfusion alone. At recall, these responses skewed towards inflammatory IgG2a (p < 0.0029) which was associated with elevated memory B cells in the spleen (p < 0.0173) and plasma blasts/plasmacells in the bone marrow (p < 0.0012). Conversely, LPS suppressed the primary alloantibody response (p < 0.0002), but at recall, suppressed only inhibitory IgG1 (p < 0.0001) with memory, plasma blasts, and plasmacell responses equivalent to transfusion alone.

Conclusions: Poly(I:C) exacerbates early inflammatory alloantibody responses after primary transfusion and upon rechallenge. Although LPS suppresses the primary alloantibody response, the recall response remains largly intact, with deficits only in inhibitory IgG1. These data suggest that recipient inflammation can alter risk of alloimmunization in complex and evolving ways, impacting both the initial response and the response to subsequent alloexposures.

Importance of research: Healthy patients are not transfused, and the illness/treatment that necessitated platelet transfusion may alter alloimmunization risk. This work shows viral-like poly(I:C) exposure elevates alloresponses to primary and subsequent transfusion whereas LPS, a bacterial component, suppresses the primary and alters the recall response. Therefore, recipient inflammation impacts alloimmunity in complex ways which could inform strategies to manage alloimmunization risk in these patients.