Haptoglobin-related protein mediates trypanosome lytic factor binding to trypanosomes

Area of Science:

• Biochemistry
• Parasitology
• Immunology

Background:

• Trypanosome lytic factor (TLF-1) is a unique high-density lipoprotein in human serum.
• TLF-1 exhibits toxicity towards Trypanosoma brucei brucei, potentially preventing human infections.
• TLF-1 comprises apolipoprotein AI, apolipoprotein AII, paraoxonase, and haptoglobin-related protein (Hpr).

Purpose of the Study:

• To investigate the mechanism of TLF-1-mediated trypanosome killing.
• To identify the specific components and receptors involved in TLF-1 binding and uptake.
• To elucidate the role of haptoglobin-related protein (Hpr) in TLF-1's biological activity.

Main Methods:

• Low-temperature binding assays to characterize TLF-1 receptors.
• Competition assays using purified Hpr, haptoglobin (Hp), and human HDL.
• Utilizing monoclonal antibodies against Hpr to block TLF-1 interactions.

Main Results:

• TLF-1 binds to trypanosomes via two distinct receptors: high-affinity/low-capacity and low-affinity/high-capacity.
• Low-affinity binding is competed by human HDL and likely mediated by apolipoprotein AI.
• Hpr and Hp bind to trypanosomes, undergo internalization, and are lysosomally targeted.
• Hpr competes for TLF-1 binding, and anti-Hpr antibodies inhibit TLF-1 uptake and trypanosome killing.

Conclusions:

• Haptoglobin-related protein (Hpr) is crucial for the high-affinity binding of TLF-1 to Trypanosoma brucei brucei.
• TLF-1 likely utilizes a haptoglobin-like receptor on trypanosomes, mediated by Hpr.
• These findings highlight Hpr's role in the antiparasitic activity of TLF-1.