The 1F7 idiotype is selectively expressed on CD5⁺ B cells and elevated in chronic hepatitis C virus infection

Antibodies against different chronic viruses, including hepatitis C virus (HCV), express a public cross-reactive idiotype (Id) designated as 1F7. The prominence of this Id may reflect selective engagement of B1 B cells by chronic pathogens. We investigated this by comparing 1F7 Id expression on CD5 ⁺ and CD5^- B cells, total IgG, total IgM and anti-HCV core antibodies in different HCV exposure settings. By flow cytometry, we observed a selective increase in 1F7 Id⁺CD5⁺ B cells in chronic HCV infection. 1F7 Id levels in different immunoglobulin compartments were measured by enzyme-linked immunosorbent assay. 1F7 Id expression was prominent in anti-HCV core antibodies of ∼90% of 141 HCV-exposed individuals tested. In the Canadian and Armenian study groups, participants who spontaneously cleared HCV infection had lower median 1F7 Id levels on total plasma IgG and anti-HCV core antibodies. Armenian spontaneous clearers, who were younger and more recently infected than their Canadian counterparts, also had had lower median 1F7 Id levels on total plasma IgM. Engagement by HCV of B-cell receptors within, or overlapping with the CD5⁺ B1 B-cell repertoire is reflected in the production of 1F7 Id⁺ anti-HCV antibodies and expansion of 1F7 Id⁺CD5⁺ B cells. Higher 1F7 Id expression levels are associated with chronic infection.