A Peptide Derived from the Parasite Receptor, Complement C2 Receptor Inhibitor Trispanning, Suppresses Immune Complex-Mediated Inflammation in Mice

Abstract

Complement C2 receptor inhibitor trispanning (CRIT) is a Schistosoma protein that binds the human complement protein, C2. We recently showed that peptides based on the ligand binding region of CRIT inhibit the classical pathway (CP) of complement activation in human serum, using hemolytic assays and so speculated that on the parasite surface CRIT has the function of evading human complement. We now show that in vitro the C2-binding 11-aa C terminus of the first extracellular domain of CRIT, a 1.3-kDa peptide termed CRIT-H17, inhibits CP activation in a species-specific manner, inhibiting mouse and rat complement but not that from guinea pig. Hitherto, the ability of CRIT to regulate complement in vivo has not been assessed. In this study we show that by inhibiting the CP, CRIT-H17 is able to reduce immune complex-mediated inflammation (dermal reversed passive Arthus reaction) in BALB/c mice. Upon intradermal injection of CRIT-H17, and similarly with recombinant soluble complement receptor type 1, there was a 41% reduction in edema and hemorrhage, a 72% reduction in neutrophil influx, and a reduced C3 deposition. Furthermore, when H17 was administered i.v. at a 1 mg/kg dose, inflammation was reduced by 31%. We propose that CRIT-H17 is a potential therapeutic agent against CP complement-mediated inflammatory tissue destruction.

Evidence of complement-mediated killing of Discocotyle sagittata (Platyhelminthes, Monogenea) oncomiracidia

“…Killing of Gyrodactylus and Schistosoma was found to be mediated via the alternative complement pathway and was suspected to occur as a result of osmotic stress following damage to the tegument by immune attack complexes [3e7]. Schistosoma has recently been found to produce peptides that inhibit complement [19,20]. In the experiments we report, the involvement of the classical pathway cannot be completely excluded since naı¨ve trout has detectable levels of anti-D. sagittata antibodies [13,21].…”

Complement C2 Receptor Inhibitor Trispanning: A Novel Human Complement Inhibitory Receptor

“…CRIT-H17 representing the 11-aa C-terminal part of CRIT-ed1 has a 10-fold order of magnitude greater affinity for C2 than CRIT-ed1. Interestingly, in preliminary unreported results before the study of Inal and Schifferli (10), CRIT-H17 alone, but not CRIT-ed1, gave significant reductions in various parameters of complement-mediated inflammation in the reversed passive Arthus reaction in mice (11). In all current experiments, C2 binding to Hu-CRIT-ed1 was not Mg 2ϩ dependent.…”

“…If soluble CRIT in the form of the CRIT-ed1 peptide or the smaller CRIT-H17 derivative peptide is not antigenic in humans, then it could potentially be used as a therapeutic agent against certain complement-mediated human diseases. The first promising tests of the in vivo efficacy of CRIT-H17 in blocking immune complex-mediated tissue injury in the classical inflammation model, the reversed passive Arthus reaction (11), and in Forsman shock (20) should be further addressed.…”

“…Finally, stained sections were mounted with permanent mounting medium (Eukitt/Fluka Chemical). Immunohistological examination was performed using a Zeiss Axiophot microscope as described before (11).…”

“…We suggest that this novel receptor with three N-terminal transmembrane (TM) domains represents a novel family of receptors and present several lines of evidence supporting CRIT as receptor for C2. The complement regulatory function of CRIT was suggested previously (10,11) by using CRIT extracellular domain 1 (ed1) and its 11-aa C terminus (CRIT-H17) to inhibit CP-mediated hemolysis in the presence of normal human serum (NHS). We have now shown that, by blocking CRIT through preincubation with anti-CRIT-ed1, two CRITexpressing human myeloid cell lines as well as monocytes, can be deprotected, resulting in increased susceptibility to Ab-dependent complement lysis in vitro.…”