Interleukin-6 is expressed at high levels in the CNS in Lyme neuroborreliosis

In patients with Lyme neuroborreliosis, inflammation and symptoms of fatigue and malaise occur out of proportion to the relatively low number of spirochetes present. Previous studies have identified interleukin-6 (IL-6) as a candidate molecule for amplification of CNS inflammation in this disease. We pursued this possibility by measuring cytokine gene expression by reverse-transcriptase polymerase chain reaction (RT-PCR) in the brain of rhesus macaques actively infected with Borrelia burgdorferi. Samples of brain tissue were screened for IL-6 and interferon gamma using RT-PCR-ELISA, a technique that uses RT-PCR, subsequent hybridization of the PCR product with a biotinylated probe, and capture and ELISA readout of hybridization product. The number of copies in positive samples was then quantitated using qRT-PCR-ELISA, in which wild-type cytokine cDNA competes with recombinant competitor DNA in the PCR. Elevated levels of IL-6 cDNA and, to a lesser extent, interferon gamma were detected in three of three nonhuman primates with persistent infection with B burgdorferi, whereas the brains of three uninfected animals had undetectable levels of gene expression of these cytokines. These data support the hypothesis that cytokines such as IL-6 are important amplification molecules for CNS inflammation in Lyme neuroborreliosis.