PhD

dissertationIn the mouse model for Lyme disease developed by Dr. Barthold and colleagues, different inbred strains of mice reproducibly display mild, moderate and severe arthritis. C3H mice develop very severe arthritis with the infection of Borrelia burgdorferi and BALB/c mice develop mild arthritis. Previous reports from our laboratory demonstrated that B. burgdorferi possesses B-cell mitogenic and cytokine stimulatory activities in vitro. These activities were subsequently shown to be properties of the two major outer surface lipoproteins of B. burgdorferi, OspA and OspB. In this dissertation, mitogenic and inflammatory cytokine responses in B. burgdorferi infected C3H/HeJ and BALB/c strains of mice were investigated. Results demonstrated that infected C3H/HeJ mice displayed a persistent 10-fold increase in circulating IgG levels, a 2-fold increase in IgM levels, and a 15-fold increase in peripheral lymph node B cells. Interleukin-6 (IL-6) levels were found to be persistently elevated in serum of infected C3H/HeJ mice. In contrast, infected BALB/c mice had low level mitogenic activity and low levels of serum IL-6. These findings indicated that mitogen induced B cells and IL-6 may be involved in the pathogenesis of severe arthritis. In vivo neutralization of IL-6, TNF-alpha and IFN-gamma did not significantly alter the arthritis development. Bacterial invasion of tissues is an important aspect of Lyme disease. The intense inflammatory responses in C3H mice could be the result of greater numbers of spirochetes. Thus, it was necessary to develop a technique to reproducibly and accurately detect B. burgdorferi in mouse tissues. In this dissertation, a sensitive and quantitative PCR technique for the detection of spirochete DNA was developed. This dissertation has demonstrated a reproducible, quantitative difference in spirochete numbers in tissues of the two strains of mice. Ankles and hearts from C3H/HeJ mice were found to harbor 10-fold more B. burgdorferi DNA than the tissues from BALB/c mice. This difference in numbers of spirochetes correlated with the severity of arthritis in these two strains of mice. Furthermore, F1 mice infected with B. burgdorferi demonstrated severe arthritis and high levels of persisting spirochete numbers, similar to the C3H parents, indicating that the susceptibility to severe arthritis is a dominant trait and is associated with the high level of persisting spirochetes. These findings may allow the mapping of genes responsible for the development of arthritis