The Classical Activation Pathway of the Human Complement System Is Specifically Inhibited by Calreticulin from Trypanosoma cruzi

Abstract

The high resistance of Trypanosoma cruzi trypomastigotes, the causal agent of Chagas’ disease, to complement involves several parasite strategies. In these in vitro studies, we show that T. cruzi calreticulin (TcCRT) and two subfragments thereof (TcCRT S and TcCRT R domains) bind specifically to recognition subcomponents of the classical and lectin activation pathways (i.e., to collagenous tails of C1q and to mannan-binding lectin) of the human complement system. As a consequence of this binding, specific functional inhibition of the classical pathway and impaired mannan-binding lectin to mannose were observed. By flow cytometry, TcCRT was detected on the surface of viable trypomastigotes and, by confocal microscopy, colocalization of human C1q with surface TcCRT of infective trypomastigotes was visualized. Taken together, these findings imply that TcCRT may be a critical factor contributing to the ability of trypomastigotes to interfere at the earliest stages of complement activation.

Immunogenic calreticulin exposure occurs through a phylogenetically conserved stress pathway involving the chemokine CXCL8

“…23,24 Interestingly, anthracyclines can stimulate the relocalization of Cne1p, the yeast ortholog of CRT, to the periphery of Saccharomyces cerevisiae cells, and genetic studies indicate that the mechanisms that regulate this process in mammals and yeast may be similar. 25 Several unicellular parasites have also been reported to expose CRT on their surface, 26,27 pointing to a broad phylogenetic conservation of the CRT exposure pathway.…”

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

“…29 It is then possible that saliva, ejected at the bite site, contains molecules that inhibit the complement proteins present in the massive blood meal that floods the first part of the insect's digestive tract. We propose that CRT, a multifunctional molecule, known to be present in salivary gland extracts from insects 30,31 and to inhibit the complement system, 19,32,33 could be responsible at least partly, for this effect (A dynamic view of this functional perception is presented in Supplemental Video).…”

“…32 Resulting inhibition of the classical pathway of the complement system is detectable. 19,32,33,39 Based on this rationale, we asked whether this capacity was present in TiCRT.…”

“…We also analyzed the S domain of TcCRT (TcS), previously obtained in our laboratory. 19 TcS was detected with a rabbit anti-TcS polyclonal antibody (previously generated in our laboratory 19 ), followed by a goat alkaline phosphataseconjugated anti-rabbit IgG antibody. As negative control, TiS (12 μg) was incubated with 3% PBS/skimmed milk, followed by a goat anti-human C1 antibody and a rabbit alkaline phosphatase-conjugated anti-goat IgG antibody.…”

“…18 Human and T. cruzi CRTs specifically bind C1, inactivating at least two of the three described pathways. 19 On the other hand, salivary gland extracts from hematophagous insects such as Lutzomyia longipalpis, Lutzomyia migonei, Panstrongylus megistus, Triatoma brasiliensis, and Rhodnius prolixus inhibit the complement system, thus favoring the feeding process. 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.…”