Formation of filopodia in Trypanosoma congolense by crosslinking the variant surface antigen

Area of Science:

• Parasitology
• Cell Biology
• Immunology

Background:

• Trypanosoma congolense is a parasitic protozoan responsible for significant livestock diseases.
• The parasite's surface is covered by a dense layer of variant surface antigen (VSG), crucial for immune evasion.
• Understanding VSG dynamics is key to developing effective antiparasitic strategies.

Purpose of the Study:

• To investigate the cellular response of Trypanosoma congolense to the crosslinking of its variant surface antigen (VSG).
• To determine the specific locations and mechanisms of VSG ligand accumulation and shedding.
• To differentiate the effects of localized VSG crosslinking from uniform antibody binding.

Main Methods:

• Exposure of Trypanosoma congolense to various crosslinking agents, including concanavalin A (Con A) and anti-VSG-IgG with protein A-gold.
• Adhesion assays using surfaces coated with poly-L-lysine and Con A, and Formvar films.
• Negative staining and transmission electron microscopy for visualizing cellular structures.
• Analysis of antibody distribution on the parasite surface.

Main Results:

• Crosslinking of VSG molecules led to rapid accumulation of ligands along the flagellar attachment site.
• Shedding of VSG-ligand complexes occurred through the formation of coat-covered vesicles and filopodia.
• These phenomena were observed following treatment with Con A, anti-VSG-IgG plus protein A-gold, and cell attachment to specific surfaces.
• Trypanosomes aggregated by primary antibodies showed vesicle and filopodia formation at contact points, unlike uniformly bound antibodies.

Conclusions:

• VSG crosslinking is a critical trigger for localized ligand accumulation and subsequent shedding in Trypanosoma congolense.
• The formation of vesicles and filopodia at points of contact indicates a specific cellular response to VSG aggregation.
• Uniform antibody binding without crosslinking does not induce these shedding mechanisms, highlighting the importance of ligand aggregation.