CD4+ T helper 1 cells facilitate regression of murine Lyme carditis

Murine Lyme borreliosis, caused by infection with the spirochete Borrelia burgdorferi, results in acute arthritis and carditis that regress as a result of B. burgdorferi-specific immune responses. B. burgdorferi-specific antibodies can attenuate arthritis in mice deficient in both B cells and T cells but have no effect on carditis. Because macrophages comprise the principal immune cell in carditis, T-cell responses that augment cell-mediated immunity may be important for carditis regression. To investigate this hypothesis, we examined the course of Lyme carditis in mice selectively deficient in B cells or alphabeta T cells. Our results show that carditis regresses in B-cell-deficient B10.A(k) mice but not in alphabeta T-cell-deficient mice, independently of the mouse strain background. Despite prominent macrophage infiltrates, hearts from B. burgdorferi-infected alphabeta T-cell-deficient mice had less mRNA for tumor necrosis factor alpha as measured by reverse transcription-PCR compared to infected control mice. Anti-inflammatory cytokine mRNA levels were equivalent. Adoptive transfer of gamma interferon-secreting CD4+ T cells into infected alphabeta T-cell-deficient mice promoted carditis resolution. These results show that alphabeta T cells can promote resolution of murine Lyme carditis and are the first demonstration of a beneficial role for CD4+ T helper 1 cells in this disease.