Phagocytosis of the Lyme disease spirochete, Borrelia burgdorferi, by cells from the ticks, Ixodes scapularis and Dermacentor andersoni, infected with an endosymbiont, Rickettsia peacockii
Mattila, Joshua T.
Munderloh, Ulrike G.
Kurtti, Timothy J.
Journal of Insect Science
MetadataShow full item record
Tick cell lines were used to model the effects of endosymbiont infection on phagocytic immune responses. The lines tested for their ability to phagocytose the Lyme disease spirochete, Borrelia burgdorferi (Spirochaetales: Spirochaetaceae), were ISE6 and IDE12 from the black-legged tick, Ixodes scapularis Say (Acari: Ixodidae) and DAE15 from the Rocky Mountain wood tick, Dermacentor andersoni Stiles. Rickettsia peacockii (Rickettsiales: Rickettsiaceae), an endosymbiont of D. andersoni, was used as a representative tick endosymbiont. 70–80% of uninfected or R. peacockii-infected IDE12 and DAE15 cells phagocytosed heat-killed borreliae and 80–90% of IDE12 and DAE15 cells phagocytosed viable spirochetes. ISE6 cells were permissive of spirochetes; less than 1% of these cells phagocytosed borreliae, and spirochetes remained adherent to the cells seven days after inoculation. Cytochalasin B blocked phagocytosis of killed and viable borreliae by IDE12 cells, and prevented phagocytosis of killed spirochetes by DAE15 cells, whereas viable spirochetes successfully invaded cytochalasin-treated DAE15. IDE12 and DAE15 cells degraded borreliae within phagolysosome-like compartments. Time-lapse microscopy showed that DAE15 cells phagocytosed borreliae more rapidly than IDE12 cells. IDE12 and DAE15 cells eliminated most adherent spirochetes within 7 days of inoculation. Thus, endosymbiont infection does not significantly interfere with the phagocytic activity of immunocompetent tick cells.
Video 1 - Phagocytosis and killing of a spirochete by a DAE15 cell. A morphologically normal GFP-expressing KS20 borrelia can be seen adhering to the LTR-stained DAE15 (lower left quadrant) prior being coiled up and ingested. Once coiled up, the spirochete enters the LTR-rich area and the GFP fluorescence is lost. Total elapsed time, 27 minutes. Video 2 - Phagocytosis and killing of a spirochete by an IDE12 cell. A morphologically normal GFP-expressing KS20 borrelia can be seen adhering to a LTR-stained IDE12 cell, is slowly coiled up by the cell and ingested. Once coiled up, the spirochete enters the LTR-rich area and the GFP fluorescence is lost. Total elapsed time, 91 min 30 sec.