OspC facilitates Borrelia burgdorferi invasion of Ixodes scapularis salivary glands
Utpal Pal, Xiaofeng Yang, Manchuan Chen, Linda K. Bockenstedt, John F. Anderson, Richard A. Flavell, Michael V. Norgard, Erol Fikrig
Utpal Pal, Xiaofeng Yang, Manchuan Chen, Linda K. Bockenstedt, John F. Anderson, Richard A. Flavell, Michael V. Norgard, Erol Fikrig
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Article Infectious disease

OspC facilitates Borrelia burgdorferi invasion of Ixodes scapularis salivary glands

Abstract

Outer surface protein C (OspC) is a differentially expressed major surface lipoprotein of Borrelia burgdorferi. ospC is swiftly upregulated when spirochetes leave the Ixodes scapularis tick gut, migrate to the salivary gland, and exit the arthropod vector. Here we show that OspC strongly binds to the tick salivary gland, suggesting a role for OspC in spirochete adherence to this tissue. In vivo studies using a murine model of Lyme borreliosis showed that while OspC F(ab)2 fragments did not influence either the viability of spirochetes or ospC gene expression, they did interfere with B. burgdorferi invasion of tick salivary glands. We then generated ospC knockout spirochetes in an infectious clone of B. burgdorferi and examined them within the vector. OspC-deficient or wild-type spirochetes persisted equally within the gut of unfed ticks and multiplied during the tick engorgement; however, unlike wild-type B. burgdorferi, the mutants were unable to invade salivary glands. Salivary gland colonization of OspC-deficient spirochetes was completely restored when this mutant was complemented in trans with a plasmid harboring the wild-type ospC gene. These studies conclusively demonstrate the importance of OspC in the invasion of tick salivary glands by B. burgdorferi, a critical step in the transmission of spirochetes from the arthropod vector to the mammalian host.

Authors

Utpal Pal, Xiaofeng Yang, Manchuan Chen, Linda K. Bockenstedt, John F. Anderson, Richard A. Flavell, Michael V. Norgard, Erol Fikrig

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Figure 1

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OspC binds to I. scapularis salivary glands. (a) FITC-labeled OspC (blac...
OspC binds to I. scapularis salivary glands. (a) FITC-labeled OspC (black bars), ErpT from B. burgdorferi N40 (white bars), and BSA (gray bars) were used to probe SGE- or FBS-coated wells. Data represent the OD450 at 15 minutes (mean ± SEM, n = 3). The differences between the binding of OspC to SGE and its binding to BSA or ErpT are highly significant (P < 0.001). (b) Direct binding of FITC-labeled OspC to the intact unfixed tick salivary gland was detected using confocal microscopy. FITC-labeled ErpT and FITC-labeled BSA were used as controls. After the tick salivary gland was probed with FITC-labeled protein (shown in green), the tissues were stained with propidium iodide to localize the nuclei of the salivary gland cells (shown in red). The objects stained green in the ErpT and BSA panels are not a part of the salivary gland. The endogenous weak green fluorescence of tick salivary glands was adjusted in the confocal microscope to compare the binding of different FITC-labeled antigens. The FITC and propidium iodide images were examined at ×400 magnification and are presented as merged images for clarity (n = 3).