Defining the complement C3 binding site and the antigenic region of Haemonchus contortus GAPDH

Area of Science:

• Parasitology
• Immunology
• Biochemistry

Background:

• Haemonchus contortus is an economically significant parasite that evades host defenses by modulating immune responses.
• Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) secreted by H. contortus inhibits the host's innate immunity, specifically the complement cascade, by binding to complement C3.
• Host immune response involves producing anti-GAPDH antibodies.

Purpose of the Study:

• To identify the complement C3 binding site and antigenic regions of H. contortus GAPDH.
• To investigate the immunogenicity and functional activity of specific GAPDH fragments.
• To evaluate the potential of a truncated GAPDH fragment as a therapeutic tool.

Main Methods:

• Generation of short recombinant fragments and deletion mutants of H. contortus GAPDH.
• Ligand overlay and plate binding assays to map C3 binding and antigenic regions.
• In vitro stimulation of host peripheral blood mononuclear cells with GAPDH fragments.
• Assessment of the stability of the truncated GAPDH moiety.

Main Results:

• The C3 binding region of GAPDH was localized to amino acids 77-114.
• An antigenic region was identified between amino acids 77 and 171.
• A truncated fragment (Fragment D, residues 77-171) retained both C3 binding activity and immunogenicity, stimulating host immune cells.
• Fragment D demonstrated stability at refrigerated temperatures for at least 12 weeks.

Conclusions:

• H. contortus GAPDH fragment 77-171 possesses both complement C3 binding and immunogenic properties.
• This truncated GAPDH moiety exhibits enhanced stability, suggesting its potential as a novel therapeutic agent against H. contortus infections.
• Understanding these interactions can lead to new strategies for parasite control.