The Interaction of Classical Complement Component C1 with Parasite and Host Calreticulin Mediates Trypanosoma cruzi Infection of Human Placenta

Abstract

Background9 million people are infected with Trypanosoma cruzi in Latin America, plus more than 300,000 in the United States, Canada, Europe, Australia, and Japan. Approximately 30% of infected individuals develop circulatory or digestive pathology. While in underdeveloped countries transmission is mainly through hematophagous arthropods, transplacental infection prevails in developed ones.Methodology/Principal FindingsDuring infection, T. cruzi calreticulin (TcCRT) translocates from the endoplasmic reticulum to the area of flagellum emergence. There, TcCRT acts as virulence factor since it binds maternal classical complement component C1q that recognizes human calreticulin (HuCRT) in placenta, with increased parasite infectivity. As measured ex vivo by quantitative PCR in human placenta chorionic villi explants (HPCVE) (the closest available correlate of human congenital T. cruzi infection), C1q mediated up to a 3–5-fold increase in parasite load. Because anti-TcCRT and anti-HuCRT F(ab′)2 antibody fragments are devoid of their Fc-dependent capacity to recruit C1q, they reverted the C1q-mediated increase in parasite load by respectively preventing its interaction with cell-bound CRTs from both parasite and HPCVE origins. The use of competing fluid-phase recombinant HuCRT and F(ab′)2 antibody fragments anti-TcCRT corroborated this. These results are consistent with a high expression of fetal CRT on placental free chorionic villi. Increased C1q-mediated infection is paralleled by placental tissue damage, as evidenced by histopathology, a damage that is ameliorated by anti-TcCRT F(ab′)2 antibody fragments or fluid-phase HuCRT.Conclusions/Significance T. cruzi infection of HPCVE is importantly mediated by human and parasite CRTs and C1q. Most likely, C1q bridges CRT on the parasite surface with its receptor orthologue on human placental cells, thus facilitating the first encounter between the parasite and the fetal derived placental tissue. The results presented here have several potential translational medicine aspects, specifically related with the capacity of antibody fragments to inhibit the C1q/CRT interactions and thus T. cruzi infectivity.

A Monoallelic Deletion of the TcCRT Gene Increases the Attenuation of a Cultured Trypanosoma cruzi Strain, Protecting against an In Vivo Virulent Challenge

“…In infective trypomastigotes, TcCRT is translocated from the ER to the area of flagellum emergence where it could hijack C1q resulting in an increased affinity for host cells [32], [33], [44]. Previous reports affirm that the C1q binding on the T. cruzi trypomastigote surface increases parasite infectivity [45] and thus, any disruption of TcCRT/C1q interaction may result in a reduction of infectivity both, in vitro and in vivo [33], [34]. Furthermore, apoptotic mammalian cells express surface ligands with high C1q affinities among them, the calreticulin orthologue.…”

Congenital Chagas disease as an ecological model of interactions between Trypanosoma cruzi parasites, pregnant women, placenta and fetuses

“…However, high concentrations of parasites induce massive destruction of the trophoblastic cells of villi explants by infecting them (Duaso et al, 2010). In vitro studies mention that T. cruzi attaches to trophoblastic cells through interactions between parasite calreticulin and C1q (Castillo et al, 2013) and induces a dis-assembly of actin in cytoskeleton. The placental alkaline phosphatase might contribute to such invasion (Sartori et al, 2002).…”

Trypanosoma cruzi infectivity assessment in “in vitro” culture systems by automated cell counting

“…The co-incubation of 10 3 or 10 6 trypomastigotes yields a reproducible infection of HPCVE (Castillo et al, 2013a;Duaso et al, 2010;Fretes and Kemmerling, 2012). However, parasite visualization and quantification are difficult in…”

“…Figure 5 Quantification of parasite DNA in the tissue by the qPCR ∆∆Ct method. HPCVE were incubated with 2 x 10 4 trypomastigotes (left column) and an inhibitor (fluid-phase HuCRT (5 µg/ml) (right column) (Castillo et al, 2013a). Genomic DNA was extracted from HPCVE with the Wizard Genomic DNA Purification Kit (Promega®, USA) according to the manufacturer's instructions.…”