Background Trypanosoma cruzi is the causative agent for Chagas Disease

1. Cestari, I. et al. (2010). Inefficient Complement System Clearance of TrypanosomacruziMetacyclicTrypomastigotes Enables Resistant Strains to Invade Eukaryotic Cells. Public Library Science.5: 11.Daniel Ma and Chakrya San

2. Background • Trypanosomacruziis the causative agent for Chagas Disease • Complements are part of the secreted effector molecules of the innate immunity that can recognize foreign invaders, leading to formation of membrane attack complex and immune system activation • 3 types of complement activation • Classical pathway via Antibody-Antigen recognition • Lectin pathway via pathogen associated molecular pattern • Alternative pathway via direct C3 recognition • Purpose • 1) Which complement pathways are activated by T. cruzi • 2) The capacity of these strains to resist the complement mediated killing at nearly physiological conditions • 3) Whether the complement system could limit or control T. cruziinvasion of eukaryotic cells. • Experimental Approach • 1) Deposition assays and in vitro assays via ELISA • 2) Kinetic assays • 3) Normal human serum at nearly physiological conditions (50% of serum at 37°C) • 4) Live/dead viability fluorescence Assay

3. Main Findings • The lectin and alternative pathways are the main activators of the complement system by T. cruzi in non-immune serum • Experimental invasion in vitro in the presence of non-immune human serum at nearly physiological conditions showed that the complement system can limit, but not avoid parasite invasion • Resistance to complement mediated killing is not a strict characteristic of the metacyclictrypomastigote stage of T. cruzi

5. Critique • It is hard to distinguish between the different strains in figure 2 • Using epimastigote to test complement is not ideal since it only exists in vectors • In the previous slide, the viability fluorescence assay tests a strain that infects primates with human serum • Invasion assay also tests a strains that do not invade primates with Vero cells (African green monkey kidney epithelial cell line) and human serum Take home message • The human complement system can kill metacyclictrypomastigotes of T. cruzi, and the ability to resist the complement system varies between the strains. • T. cruzi strains activate mainly the lectin and alternative pathways of the complement system.

6. Discussion • The innate immunity molecules (complements) are fairly conserved across species, so it is okay to test different stages of trypanosome against it. • T. cruzi invades cells quickly to escape complement killing. • In figure 3B, the reason why the survival rate goes up at 10 minutes may be because 1) counting error or 2) T cruzi that is resistant to killing has multiplied. • Testing a broad range of strains is required for a good study. • Did not explain future experiments • Strains that are resistant to killing had more invasions. • Invasion does not necessary lead to disease • Lectin is a sugar binding protein that can recognize motifs on the parasite.