The Role of Salivary and Intestinal Complement System Inhibitors in the Midgut Protection of Triatomines and Mosquitoes

Abstract

Saliva of haematophagous arthropods contain biomolecules involved directly or indirectly with the haematophagy process, and among them are encountered some complement system inhibitors. The most obvious function for these inhibitors would be the protection of the midgut against injury by the complement. To investigate this hypothesis, Triatoma brasiliensis nymphs were forced to ingest human serum in conditions in which the protection of midgut by the inhibitors is bypassed. In these conditions, the anterior midgut epithelium was injured by the complement, causing cell death. Once some insects such as Aedes aegypti have no salivary inhibitors, we hypothesized the existence of intestinal inhibitors. The inhibitory activity was investigated in the intestine of A. aegypti as well as in the saliva and intestine of other three triatomine species (T. brasiliensis, T. infestans and Rhodnius prolixus) using an immunological method able to determine the level of deposition of some complement factors (C1q, C3b, or C4b) on the surface of complement activator molecules linked to microplates. This methodology permitted to identify which points along the activation phase of the complement cascade were inhibited. As expected, soluble contents of A. aegypti's intestine was capable to inhibit C3b deposition by the classical and alternative pathways. Saliva or soluble intestinal contents, obtained from triatomines were unable to inhibit C1q deposition by the classical pathway. C4b deposition by the classical pathway was inhibited by the intestinal contents from the three triatomines. On the other hand, only T. brasiliensis saliva inhibited C4b deposition. Both, saliva and intestinal contents from all triatomines were able to inhibit C3b deposition in the classical and alternative pathways. None of the material extracted from the intestinal cell membranes from the triatomines inhibited C3b deposition in the classical pathway. The existence of complement inhibitors may have important biological consequences which are discussed in detail.

Intestinal aspartate proteases TiCatD and TiCatD2 of the haematophagous bug Triatoma infestans (Reduviidae): Sequence characterisation, expression pattern and characterisation of proteolytic activity

“…The possibility of another function is supported by the conditions in the small intestine. The activity optimum of pH 3.5 in determinations of the proteolysis of haemoglobin (Terra et al, 1988) or pH 3.0 by using fluorescence substrates (present investigation) is far away from the pH conditions in the gut of triatomines, which range between pH 5.2 and pH 6.7 in T. infestans and pH 7.02 and pH 7.16 in T. brasiliensis stomach (Barros et al, 2009). In T. brasiliensis only the pH value of the stomach in the first 24 h after blood feeding was measured.…”

An Inhibitor of the Alternative Pathway of Complement in Saliva of New World Anopheline Mosquitoes

“…Nunn et al (10) characterized OmCI, a salivary protein from the soft tick Ornithodoros moubata, that inhibits both the CP and AP. Anti-complement activity has also been reported in salivary gland homogenates of phlebotomine sandflies (11, 12) and triatomine bugs (13), highlighting the importance of the inhibitors for hematophagous arthropods. By inhibiting the C, the saliva of such arthropods is able to block the production of potent anaphylatoxins, diminishing the inflammatory response at the bite site and favoring a successful blood meal by the vector (14).…”

Triatoma infestans Calreticulin: Gene Cloning and Expression of a Main Domain That Interacts with the Host Complement System

“…However, the success of the hematophagic process also depends on innate and adaptive immune responses and, specially, on the complement system. 12 The vertebrate complement system is a component of the immune response that has approximately 30 soluble and integral membrane proteins. 13 It has three main macromolecular recognition modules (C1, mannan-binding lectin [MBL], and ficolins) that recognize diverse microorganism-associated molecular patterns ("danger signals"), through three activation routes.…”

“…20 Moreover, it has been probed that T. brasiliensis forced to ingest serum in conditions in which the protection of midgut by salivary inhibitors is bypassed, and showed damage by complement in the anterior midgut epithelium and cell death. 12 To address the role of salivary CRT on the hematophagous feeding process, we have cloned and characterized TiCRT and its S domain (TiS). Herein, we show that recombinant TiS (rTiS) binds human C1 and inhibits the classical pathway of complement activation in vitro.…”