Extra- and intracellular atypical and cystic forms of spirochetes in the cerebral cortex of a patient with pathologically and serologically confirmed chronic Lyme neuroborreliosis where Borrelia burgdorferi sensu stricto was cultivated from the brain. A: Colony-like agglomeration of spirochetes as revealed by monoclonal anti-OspA antibody in the cerebral cortex. B: A close up of the central part of the mass seen in A. In addition to a few helically shaped spirochetes (arrow) numerous ring-shaped forms and spherules (asterisk) are visible, which are identical to those observed in vitro following 1 week Borrelia exposure of primary neurons (compare with Fig. 4G). C: Spirochetes showing loop or ring-shaped formations (arrows) in the cerebral cortex immunostained with a polyclonal anti-Borrelia burgdorferi antibody (Biodesign, B65302R). They are similar to those of Treponema pallidum (arrows in D) observed in the cerebral cortex of a patient with general paresis. Immunostaining was performed using a polyclonal anti-Treponema pallidum antibody (Biodesign, B65210R). E: Helically shaped OspA immunoreactive spirochetes in the cytoplasm of a cortical pyramidal neuron. In addition to one more typical form (arrow), fine OspA positive minute granules along filamentous forms are seen. F: Intracellular ring-shaped forms (arrow) showing positive immunoreaction with a polyclonal anti-Borrelia burgdorferi antibody (BB1017). They are identical to those observed in chicken primary neurons infected with Borrelia (compare F with Figure 4D). Near the asterisk a large strongly immunoreactive cyst form is visible. Spirochete forming loop in the cerebral cortex (G) and in the cytoplasm of an epithelial cell of the choroid plexus (H) are seen as visualized by anti-OspA and anti-bacterial peptidoglycan antibodies, respectively. I: A similar atypical spirochete forming loops in the cerebral cortex as visualized with Thioflavin S. J: In an area with colony-like spirochete aggregation in addition to some typical, regularly coiled Borrelia spirochetes (arrow) OspA positive cystic forms (asterisk) are seen. K: In the cerebral cortex near the colony-like spirochetal agglomerate a spirochete cyst (asterisk) similar to that observed in vitro is visible (compare it with Figure 5 G-J). Immunostaining was performed using a monoclonal anti-OspA antibody. Bars: A = 20 μm; B-J = 10 μm, K = 5 μm. Panels C and E were reprinted from panels F and D of Figure 5 of Mikossy et al., 2004 , with permission from IOS Press.