Abstract
Tick salivary glands produce complex cocktails of bioactive molecules that facilitate blood feeding and pathogen transmission by modulating host hemostasis, pain/itch responses, wound healing, and both innate and adaptive immunity. In this study, cutaneous responses at Dermacentor andersoni bite-sites were analyzed using Affymetrix mouse genome arrays and histopathology at 12, 48, 96 and 120 h post- infestation (hpi) during primary infestations and 120 hpi during secondary infestations. The microarray data suggests: (1) chemotaxis of neutrophils, monocytes, and other cell types; (2) production and scavenging of reactive oxygen species; and, (3) keratin- based wound healing responses. Histological analysis supported the microarray findings. At 12 hpi, a mild inflammatory infiltrate was present in the dermis, especially concentrated at the junction between dermal connective tissue and underlying adipose tissue. A small lesion was located immediately under the hypostome and likely represents the feeding “pool.” Surprisingly, at 48 hpi, the number of inflammatory cells had not increased from 12 hpi, perhaps mirroring the reduction in gene expression seen at this time point. The feeding lesion is very well defined, and extravasated erythrocytes are readily evident around the hypostome. By 96 hpi, the inflammatory infiltrate has increased dramatically and the feeding lesion appears to have moved deeper into the dermis. At 120 hpi, most of the changes at 96 hpi are intensified. The infiltrate is very dense, the epidermis is markedly thickened, the feeding lesion is poorly defined and the dermal tissue near the hypostome appears to be loosing its normal architecture. In conclusion, during D. andersoni feeding infiltration of inflammatory cells increases across time concurrent with significant changes in the epidermal and dermal compartments near the feeding tick. The importance of changes in the epidermal layer in the host response to ticks is not known, however, it is possible the host attempts to “slough off” the tick by greatly increasing epithelial cell replication.
Highlights
Hard (Ixodid) ticks are important vectors of disease world- wide, making them a significant threat to public health
This heatmap suggested a similar gene expression profile for the first three time points (12, 48, and 96 hpi during primary infestations) that shifted to a second pattern that was similar between 120 hpi in primary and secondary infestations
Downregulated genes included a minor collagen, the cytoskeletal component spectrin, and a little-studied molecule Limch1 (LIM and calponin homology domains 1). These results suggest a keratin intermediate filamentbased wound healing response is activated at the tick feeding lesion, it is surprising that other cytoskeletal elements are downregulated, a pattern that is even more striking in the early primary infestation as discussed below
Summary
Hard (Ixodid) ticks are important vectors of disease world- wide, making them a significant threat to public health. Tick saliva is a complex mixture of molecules that has been shown to inhibit a broad range of host responses and facilitate pathogen transmission, while host responses can, in some cases, inhibit the feeding process and block pathogen transmission (Titus et al, 2006; Kazimírová and Štibrániová, 2013; Wikel, 2013) Hard ticks have been divided into two main phylogenetic lineages, the prostriates (containing the genus Ixodes) and the metastriates (containing all other hard tick genera). Histopathological analysis of bite-site lesions from primary infestation time points and quantitative real-time PCR analysis of lymph nodes from secondary infestation time points were analyzed These studies allow us to describe the cutaneous host response during primary and secondary infestations, measure changes in gene expression patterns across time, view potential patterns related to tick immuno-suppression, correlate www.frontiersin.org
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