Mutations in the putative HCV-E2 CD81 binding regions and correlation with cell surface CD81 expression.

Area of Science:

• Virology
• Immunology
• Genetics

Background:

• The hepatitis C virus (HCV) E2 envelope protein interacts with CD81, influencing B and T cell responses.
• Previous in vitro studies indicated higher CD81 binding affinity for HCV subtype 1a E2 proteins compared to subtype 1b.
• The in vivo correlation between mutations in E2 binding regions, HCV subtypes, and CD81 expression remained unclear.

Purpose of the Study:

• To investigate CD81 expression on lymphocytes in chronic hepatitis C patients infected with different HCV subtypes.
• To analyze mutations within the putative CD81 binding regions of the E2 gene, including HVR2, across various HCV subtypes.
• To correlate in vitro binding affinities with in vivo CD81 expression levels.

Main Methods:

• Fluorescence activated cell sorter (FACS) analysis of CD81 expression on blood lymphocytes.
• Direct sequencing of the E2 gene's putative CD81 binding regions (HVR2, codons 474-495 and 522-552).
• Comparison of CD81 expression and mutation frequencies between HCV subtypes 1a, 1b, and 3.

Main Results:

• Significantly higher CD81 expression on CD8(+) T-lymphocytes was observed in patients infected with HCV subtype 1a compared to subtypes 1b and 3.
• HCV subtype 1a isolates exhibited a highly conserved motif within HVR2 and fewer mutations in putative CD81 binding regions (low percentage).
• HCV subtype 1b isolates showed numerous mutations (23.6%), while subtype 3 isolates had intermediate mutation rates (19.2%) in these regions.

Conclusions:

• The conserved E2 sequence in HVR2 and CD81 binding sites of HCV subtype 1a is linked to high in vitro CD81 binding affinity.
• This conserved sequence correlates with elevated CD81 expression on CD8(+) T-lymphocytes in vivo.
• Findings highlight subtype-specific differences in HCV-CD81 interactions and their immunological consequences.