Abstract
Lyme borreliosis is a systemic disease involving the skin, the musculoskeletal system, the
heart and the central nervous system. The shift of the cytokine pattern towards the Th1
response is one characteristic feature of the disease. Recently, interleukin-18 has been
described to induce interferon-gamma. Therefore the potential role of IL-18 in Lyme disease
has been studied. In addition, it is not clear how the spirochetes can disseminate within the
host organism. Therefore, the potential induction of metalloproteinases (MMPs) by B.
burgdorferi was observed. Serum samples from patients with Lyme disease (n = 100) were
collected (Lyme arthritis; n = 65, other manifestations of Lyme disease n = 35). Normal blood
donors (n = 37) and patients with rheumatoid arthritis (RA; n = 12) served as controls. IL-18
levels were determined by ELISA. In patients with Lyme arthritis IL-18 was significantly
elevated (median value 179 pg/ml; p < 0.01) as compared to normal controls (0,05 pg/ml).
Patients with RA had significantly higher levels compared to normal controls, too (162 pg/ml).
Collagenase-1 (MMP-1) and stromelysin (MMP-3) as well as tissue inhibitor of
metalloproteinases-1 (TIMP-1) had no significant different levels in patients with Lyme
Borreliosis compared to healthy donors. The significant elevation of IL-18 in sera of patients
with Lyme disease implies a pathophysiological role of this cytokine. Additional studies will
have to show if IL-18 reflects the activity of the disease and may be useful as a novel marker
in diagnosis and therapy of Lyme borreliosis. The potential secretion and induction of IL-18,
MMPs and TIMP-1 by Borrelia burgdorferi was tested using a novel threedimensional in-vitro
model of Lyme arthritis. Explant cultures of human synovial tissue were infected with B.
burgdorferi. and co-cultered for up to 72 hours. The concentrations of IL-18, MMP-1, MMP-3
and of TIMP-1 were measured by ELISA. The activities of gelatinase A (MMP-2) and B
(MMP-9) were assessed by zymography. Moreover, a semiquantitative RT-PCR was used to
determine the induction of TNF-alpha, IL-1beta, IL-18, MMP-1, MMP-2, MMP-3 and MMP-9
mRNA. After 72 hours, the infected cultures showed an increase of IL-18 concentrations up
to the 1.3 fold of the levels at 24 hours after infection. In uninfected controls the IL-18 level
after 72 hours was reduced to 80 % of the level at 24 hours. Furthermore, in the infected
cultures there was an increase of MMP-1 levels compared to the uninfected cultures,
whereas no increase of MMP-3 concentrations was observed. Of note, there was a reduction
of TIMP-1 levels in the infected cultures. The RT-PCR results showed MMP-1 and MMP-3 to
be induced by B. burgdorferi. By zymography, a slightly increased activity of MMP-9 in the
infected cultures could be demonstrated, MMP-2 had activity in all supernatants. Spirochetes
themselves did not produce MMP-2 or MMP-9. An increase of IL-18 could be demonstrated
in 2/4 cultures infected with B. burgdorferi. B. burgdorferi is able to induce proteolytic
enzymes of the host. Moreover, the spirochetes reduce the TIMP-1 production, pointing
towards an imbalance between the proteases and their inhibitor. This may reflect a
mechanism potentially operative in vivo that enables the microorganism to penetrate host
barriers. In addition, the local release of MMPs within the joint may contribute to the
pathophysiology of Lyme arthritis like in other inflammatory arthritides such as rheumatoid
arthritis. |
