A reassessment of argasid tick salivary gland ultrastructure from an immuno-cytochemical perspective

Abstract

Previous morphological and histochemical studies of argasid tick salivary glands indicated that they were less complex than ixodid salivary glands, with only three granular cell types. The present study shows that there exist at least four different granular cell types in the salivary glands of the argasid tick Ornithodoros savignyi, based on immuno-localization of the anti-hemostatic factors, apyrase and savignygrin. Both anti-hemostatic factors were localized to dense core granule type 'a' and to granule type 'b', that shares a similar homogenous morphology with non-labeled granule type 'd'. Furthermore, the major tick salivary gland proteins (TSGPs), previously implicated in granule biogenesis, were localized to all the granular cell types. This indicates that granular cell types with different morphologies can express the same proteins, while cell types that show similar morphologies may not express the same proteins. Argasid tick salivary glands seem to be more complex than previously thought and might not be amenable to morphological classification alone. Alternative classification methodologies that rely on physical expression patterns of the salivary gland proteome might be more reliable as markers for a specific granular cell type.

Comparative sialomics between hard and soft ticks: Implications for the evolution of blood-feeding behavior

“…Even so, it is of interest that soft tick glands show such a good correlation between transcript and protein abundance. Soft tick salivary glands are normally filled with large secretory granules where proteins are stored until secretion during feeding (Roshdy, 1972, Roshdy and Coons, 1975, Coons and Roshdy, 1981, El-Shoura, 1985, 1987Mans et al, 2004). Ticks, such as A. monolakensis, may only feed once a year and in the periods in between, granules will be stationary.…”

Tick anti-hemostatics: targets for future vaccines and therapeutics

“…Expression library immunization (ELI) with the putative nucleotidase from I. scapularis showed a 50% reduction in tick infestation [44]. Antiserum raised against the O. savignyi apyrase indicated it to be antigenic [45]. Cross-protection and adverse effects have not been investigated on the host.…”

“…Although both ixodegrins and variabilin exhibit their function through a RGD motif, variabilin lacks the cysteine-stabilized loop that is involved in presentation of the functional motif [52]. To date, only the antigenicity of savignygrin has been demonstrated [45]. The efficacy of platelet aggregation and adhesion inhibitors as vaccine candidates remains unaddressed.…”

Borrelia hermsii Acquisition Order in Superinfected Ticks Determines Transmission Efficiency

“…2, in which GGI and GGII spirochetes primarily colonized separate granular acini and were never observed in agranular acini, suggests the latter are inaccessible to spirochetes or do not support their growth. A more precise model of B. hermsii infection of salivary glands has to correlate patterns of spirochete localization and release with the secretory functions of acini, as initiated with studies in Ornithodoros savignyi (25).…”