Abstract 16744: Antibody Responses to Myocardial Antigens Released in the Context of a Myocardial Infarction

Abstract

Our study aims to investigate antigen-specific B cell responses after myocardial infarction. Recent research has indicated that B cells and myocardial antibodies may contribute to the development of ischemic heart failure and dampen post-myocardial infarction repair. However, the antigen specificity of these myocardial antibodies remains unknown. To produce high-affinity antibodies, B cells typically undergo multiple rounds of somatic hypermutation and selection processes within the germinal center (GC) reactions of secondary lymphoid organs. Therefore, we sought to characterize the germinal center B cell responses and to examine the repertoire of B cell receptors (BCR) in C57BL/6J mice subjected to experimental myocardial infarction. Flow cytometry analyses showed increased frequencies of GC B cells in infarcted mice at 5 and 14 days post-surgery. However, sham-operated mice also showed similar increase in GC frequencies on day 14 post-surgery. Single-cell RNA/BCR sequencing analyses enabled the identification of GC B cell and plasma cell (antibody secreting) populations expressing unique B cell receptors in infarcted mice that were not found in sham-operated mice. Over time, the number of GC B cells increased accompanied by a progressive clonal expansion, indicating the development of antigen-driven B cell responses. By examining immunoglobulin variable gene rearrangements within single B cells, we identified distinct B cell lineages expressing mutated antigen receptors suggestive of affinity maturation. Selected BCRs of interested were then cloned into immunoglobulin expression vectors and expressed in immortalized human embryonic kidney cells. When incubated with histological myocardial slices, one of these unique BCR expressed showed binding to myocardial antigens. These findings support the notion that myocardial infarction can trigger germinal center B cell responses, which then lead to the production of high-affinity heart-specific antibodies. Moreover, the ‘track-and-clone’ approach herein described could help unraveling the antigen specificity and functional significance of these myocardial antibodies.