Host immune response evasion strategies in Ornithodoros erraticus and O. moubata and their relationship to the development of an antiargasid vaccine

Abstract

We analysed in mice why the salivary gland extract (SGE-2) from Ornithodoros erraticus and O. moubata induce a protective response with Freund's adjuvants (FAs) in swine while the saliva, in natural conditions, does not. Such protection has been ascribed to the fact that administration of SGE-2 plus FAs permits the recognition of certain salivary components that under natural conditions are not immunogenic. The present findings confirm this hypothesis since in mice, which are unable to recognize the above components, the SGE-2-FAs do not induce any protection. We rule out the possibility that the cause of this could lie in the absence of prostaglandin E2 in the SGE-2 (vs saliva) since it is not present in either fluid. Neither could it be due to a change in antibody isotype since those induced by parasites bites and by the SGE-2-FAs are the same (IgG2a > IgG1 > IgG2b; not IgG3, IgM, IgE). No IgG2a were seen when the SGE-2 were administered alone or with alum or ricin. It is therefore suggested that first responses would be Th1 and the second ones Th2, although no IgE is seen in the latter responses either. The parasites do not require complement to feed; by contrast, they block its activation and skin cellular infiltrates, such as those elicited by IL-8, MCP-1 and C5a, do not affect them, regardless of the presence or not of antitick antibodies.

Complement Inhibitor of C5 Activation from the Soft Tick Ornithodoros moubata

“…Although evidence supports C-mediated tick resistance (9 -12) and the existence of C inhibitors in ticks (17)(18)(19)(20), only one other C inhibitory molecule from the hard tick I. scapularis has previously been identified and expressed (18). The primary sequence of OmCI is unrelated to the I. scapularis protein and has no sequence similarity to the N-terminal sequence of O. moubata Ag 20A1 (33), which was proposed to be the factor responsible for C inhibition in SGE of O. moubata and O. erraticus (20). Indeed, OmCI has no detectable sequence similarity to any known C inhibitors in public databases.…”

“…TSGP2 is toxic to mice but TSGP3 is not (34). OmCI is highly unlikely to be a toxin because O. moubata does not cause toxicosis (20), whereas O. savignyi causes sand tampan toxicosis in a wide range of mammals (34). Furthermore, intradermal injection of 100 g of purified nOmCI into guinea pigs, in the process of raising antisera, caused no obvious pathophysiological effects (M. Nunn, unpublished observation).…”

“…A distinct salivary anaphylatoxin inactivating activity has been reported in the same species (19). Classical and alternative pathway C inhibitory activity has previously been recognized in O. moubata salivary gland extract (SGE) but the active components have not been identified (20).…”

Ancestral reconstruction of tick lineages

“…No PGE2 has been detected in argasid saliva, nor does it stimulate salivary secretion, suggesting that it does not exist in soft ticks (Astigarraga et al 1997;Mans, 2014;Maritz-Olivier et al 2005). This correlates with the secretion of bloodmeal-derived water via the coxal glands and the absence of acini III in argasids ticks (Balashov, 1972;Coons and Alberti, 1999).…”

Antihemostatic Molecules from Saliva of Blood-Feeding Arthropods

“…Hard ticks (Acari: Ixodidae) use salivary prostaglandins, including prostacyclin, PGE 2 , and PGF 2 ␣ , to accomplish vasodilation in their hosts [28] . Although the vasodilators from soft ticks (Acari: Argasidae) have yet to be characterized, they apparently do not produce prostaglandins [29] . These examples suggest that the diversity of vasodilators awaiting discovery may be even larger than what might be predicted from the number of families with the blood-feeding habit.…”