Direct enumeration of Borrelia-reactive CD4 T cells ex vivo by using MHC class II tetramers

Abstract

We characterized antigen-specific CD4+ T cells in six patients with treatment-resistant Lyme arthritis, using an HLA-DRB1(*)0401 major histocompatibility complex (MHC) class II tetramer covalently loaded with OspA164-175, an immunodominant epitope of Borrelia burgdorferi. Direct analysis of OspA-tetramer binding CD4+ cells in patients expressing the HLA-DRB1(*)0401 allele revealed frequencies of between <0.005 and 0.1% in peripheral blood (n = 6), and between <0.005 and 3.1% in synovial fluid (n = 3). OspA-tetramer+CD4+ cells were directly cloned at I cell per well and expanded by mitogen and IL-2 on allogeneic feeder cells. As measured by [3H]thymidine incorporation, 95% of 168 T cell clones from synovial fluid binding the OspA-tetramer were antigen-reactive. Clones generated from peripheral blood revealed a different pattern of responsiveness when compared with clones generated from synovial fluid, as measured by proliferation, IFN-γ, and IL-13 secretion. These clones, selected on the basis of their peptide binding, also responded to whole protein, but with a different cytokine profile. Our studies demonstrate that MHC class II tetramers can be used in humans to directly identify, isolate, and characterize antigen-reactive T cells from an inflammatory compartment.