Page 73 - Human Lyme Neuroborreliosis

Non-human Primate Animal Models 57

To better understand the relationship between chronic infection,
antispirochetal immunity and inflammation in LNB, Pachner and colleagues
[13] measured spirochetal density in CNS and PNS tissues by PCR and
correlated them to anti-B. burgdorferi antibody in the serum and CSF, and to
inflammation in tissues of 8 rhesus monkeys with experimental LNB. Their
findings identified the CNS and PNS as major reservoirs of spirochetal
infection and demonstrated that a strong, well-developed anti-B. burgdorferi
humoral immune response did not clear spirochetes from the animal during the
months of infection, especially in the nervous system. Spirochetal presence
was a necessary but not sufficient condition for inflammation. Despite the
presence of spirochetes in CNS tissue, there was little inflammation and no
intrathecal antibody production in the CNS in contrast to strong systemic
antibody production and marked inflammation in cardiac and skeletal muscle
tissue. Two methods of spirochete inoculation, by needle injection of 1 million
N40Br strain spirochetes and feeding of infected ticks were found to be
comparable in establishing infection. Transient immunosuppression was
employed to maximize the yield of infection in some of the NHP. The
presence of spirochete infection was demonstrated by identifying B.
burgdorferi DNA in multiple tissues by PCR, with a load that varied in
nervous system tissue. The authors [13] constructed at least three important
hypotheses which were tested in this NHP model of LNB. First, that
spirochetes would be found by PCR diffusely throughout the CNS and PNS,
and this was supported by the results. The density of spirochetes per milligram
of tissue or microgram of extracted DNA was found to be lower in the
immunocompetent NHP relative to immunosuppressed NHP but spirochete
densities were uniform in all tissues with CNS loads essentially identical to
other tissues, and at levels close to those in immunosuppressed NHP. This
provided evidence that spirochetes in CNS tissue were protected from
immune-mediated clearance relative to spirochetes in the peripheral nerve and
skeletal muscle [14, 15].

Second, the authors [13] hypothesized that the spirochete load correlated
with the anti-B. burgdorferi antibody response and that the former drove the
latter, however there was no consistent correlation of the two as measured by
ELISA. The amplitude of the IgG response by ELISA and the number of B.
burgdorferi protein bands identified on Western blot increased with increasing
duration of infection. The height and complexity of the IgG response in NHP
LNB was likely important for spirochete clearance in the CNS. In other
experiments, NHP treated with corticosteroids that mounted a high titer IgM
response with a negligible IgG response had very high levels of spirochetes in

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