Elevated LAG-3 on CD4⁺ T cells negatively correlates with neutralizing antibody response during HCV infection

Lymphocyte activation gene-3 (LAG-3), an inhibitory molecule, which has been shown co-expressed with multiple inhibitory receptors on CD8⁺ T and natural killer (NK) cells and negatively regulates T and NK cell responses during hepatitis C virus (HCV) infection. However, whether LAG-3 is involved in the regulation of the antibody response remains unclear. This study aims to investigate the relationship of LAG-3 with neutralizing antibody (nAb) response during HCV infection. A total of 66 HCV-infected individuals and 36 sex- and age-matched healthy controls from a population of intravenous drug users were recruited. Circulating follicular helper T (cTfh) cells and LAG-3-expressing CD4⁺ T cells, type 1 regulatory T (Tr1) cells, and regulatory T (Treg) cells were characterized by flow cytometry. Serum nAb response of HCV-infected individuals was determined using pseudoparticle neutralization assays. We found that HCV infection enhanced LAG-3 expression on CD4⁺ T cells and exhibited regulatory T cell-like phenotype and inversely associated with the HCV nAb response. Further analysis showed that frequency of CXCR3⁺ cTfh cells positively correlated with nAb response, however LAG-3⁺ CD4⁺ T cells inversely associated with CXCR3⁺ cTfh cells. This study observed that LAG-3⁺ CD4⁺ T cells exhibit a regulatory cell phenotype and negatively associate with the HCV nAb response, implying that LAG-3 may be involved in the negative regulation of humoral immunity during HCV infection.