Reduced number of interleukin-12 secreting cells in patients with Lyme borreliosis previously exposed to Anaplasma phagocytophilum.

Lyme borreliosis and human granulocytic ehrlichiosis are tick-borne diseases caused by Borrelia burgdorferi and Anaplasma phagocytophilum, respectively. Infection with A. phagocytophilum has been observed to induce immunosuppression and animal studies suggest that the bacteria might also have prolonged inhibitory effects on immune cells. The aim of this study was to investigate the cytokine secretion in patients exposed previously to A. phagocytophilum and currently infected with B. burgdorferi compared with patients infected with B. burgdorferi and seronegative for A. phagocytophilum. Eight patients with erythema migrans and antibodies against A. phagocytophilum, 15 patients with erythema migrans and negative A. phagocytophilum serology and 15 non-exposed healthy individuals were included in the study. Blood mononuclear cells were stimulated with Borrelia-antigen and the number of cytokine [interleukin (IL)-4, IL-5, IL-12, IL-13 and interferon (IFN)-gamma]-secreting cells was detected by enzyme-linked immunospot (ELISPOT). This study shows that patients with a previous exposure to A. phagocytophilum and a current infection with B. burgdorferi have a lower number of Borrelia-specific cells secreting IL-12 compared to Ap seronegative patients infected with B. burgdorferi (P < 0.001), indicating impairment in the ability to mount strong Th1-responses. We suggest that this mirrors a reduced Th1 response caused by A. phagocytophilum which could influence the outcome of the Borrelia infection and, speculatively, may also have implications in other conditions.