Inhibition of Borrelia burgdorferi migration from the midgut to the salivary glands following feeding by ticks on OspC-immunized mice

Abstract

Borrelia burgdorferi-infected ticks were fed on either OspC-immunized mice or normal, nonimmunized mice. After 72 h, the ticks were detached, followed by dissection and subsequent culturing in Barbour-Stoenner-Kelley II medium of the salivary glands from each tick to determine the presence of borreliae. Forty percent (10 of 25) of salivary glands from ticks that had fed on nonimmunized mice were culture positive, while only 7.4% (2 of 27) of salivary glands from ticks that had fed on OspC-immunized mice were culture positive, thus indicating a much reduced borrelial migration from the midgut when the bloodmeal contained anti-OspC antibodies. Fluorescent antibody staining of the corresponding midguts from ticks that had fed on the OspC-immunized mice showed that borreliae were present but did not produce OspC. In contrast, borreliae in midguts from ticks that had fed on normal mice demonstrated substantial ospC expression. This study provides evidence that, during tick feeding on an OspC-immunized host, transmission of borreliae from the tick is prevented; it also suggests that OspC functions in a tick-to-host transmission mechanism.

FIG. 1

Representative fields of double immunofluorescent staining of B. burgdorferi in tick midguts following tick feeding at 72 h. (A) Borreliae in ticks which had fed on a normal nonimmunized mouse stained with FITC-labeled anti-whole-cell B. burgdorferi. (B) Same field as in panel A, stained with rhodamine-labeled anti-OspC. Arrows indicate some of the borrelial cells expressing OspC in panel B with the corresponding cells in panel A. Note that not all cells seen in panel A express OspC, as seen in panel B. (C) Borreliae in ticks which had fed on an OspC-immunized mouse stained with FITC-labeled anti-whole-cell B. burgdorferi. (D) Same field as in panel C, stained with rhodamine-labeled anti-OspC.

FIG. 2

Indirect immunofluorescence assay of B. burgdorferi incubated with anti-OspC antibodies. (A) Dark-field microscopy of input organisms cultured in vitro prior to incubation in the borreliacidal assay mixture. (B) Same field as in panel A, stained with FITC-labeled anti-OspC MAb. Note that most, but not all, borreliae express OspC. (C) Dark-field microscopy of B. burgdorferi from the borreliacidal assay incubated with anti-OspC. (D) Same field as in panel C, stained with FITC-labeled anti-OspC. Panels C and D represent fields seen whether borreliae were incubated with protected mouse polyclonal anti-OspC sera or with the OspC MAb at 24 or 72 h. Arrows in panels A and C indicate borrelial cells that have formed clumps.