Single Cell Immunophenotyping of Lyme Erythema Migrans (Bulk TCR Repertoire Sequencing)

Erythema migrans (EM) is a skin lesion caused by the spirochete B. burgdorferi (Bb) and is a hallmark initial sign of Lyme disease. Previous studies have demonstrated that T cells and innate immune cells mediate local inflammatory cytokine production that promote the reaction. Despite the established importance of B cells and antibodies in preventing Bb infection and resolving disease, the role of B cells in the skin immune response to Bb is incompletely defined. In this study, we characterized the immunophenotype of EM lesions and used single cell RNA-Seq to investigate B cell receptor (BCR) and T cell receptor (TCR) repertoires in the EM skin lesions and peripheral blood of patients with Lyme disease. We hypothesized that B cells from the circulation, potentially primed by exposure to Bb antigens in regional draining lymph nodes, are recruited into EM lesions and play an active role in the local response to infection. We found that B cells are more abundant in the EM lesion in comparison to autologous uninvolved skin and possess distinct characteristics, including abundant expression of MHCII genes and preferential IgM isotype usage. A subset exhibited low levels of somatic hypermutation despite a gene expression profile more consistent with memory than naïve B cell subsets. Moreover, infiltrating B cells were clonally expanded and a large fraction could be directly traced to circulating relatives. By leveraging single cell gene expression with paired BCR and TCR repertoire sequencing, we demonstrate, for the first time, that B cells are recruited to the skin infection site in early Lyme disease and express a phenotype suggesting that they could play a role in local antigen presentation and antibody production. Bulk TCR sequencing was performed on PBMCs from six subjects, all with confirmed cases of Lyme disease.