Comparative characterization of B cells specific for HBV nucleocapsid and envelope proteins in patients with chronic hepatitis B

Abstract Background & Aims Knowledge about the regulation of anti-HBV humoral immunity during natural HBV infection is limited. We recently utilized dual fluorochrome-conjugated HBsAg to demonstrate, in patients with chronic HBV (CHB) infection, the functional impairment of their HBsAg-specific B cells. However, the features of their HBcAg-specific B cells are unknown. Here we developed a method to directly visualize, select and characterize HBcAg-specific B cells in parallel with HBsAg-specific B cells. Methods Fluorochrome-conjugated HBcAg reagents were synthetized and utilized to detect directly ex vivo HBcAg-specific B cells in 36 CHB patients. The frequency, phenotype, functional maturation and transcriptomic profile of HBcAg-specific B cells was studied by flow cytometry, in vitro maturation assays and Nanostring based detection of expression of immune genes, which we compared with HBsAg-specific B cells and total B cells. Results HBcAg-specific B cells are present at higher frequency than HBsAg-specific in CHB patients and, differently to HBsAg-specific B cells, they mature efficiently into antibody-secreting cells in vitro. Their phenotypic and transcriptome profiles show that HBcAg-specific B cells are preferentially IgG+ memory B cells. However, despite their phenotypic and functional differences, HBcAg- and HBsAg-specific B cells of CHB patients share a mRNA expression pattern that differs from global memory B cells and is characterized by high expression of genes indicative of cross-presentation and innate immune activity. Conclusions During chronic HBV infection, a direct relation exists between serological detection of anti-HBs and anti-HBc antibodies and quantity and function of their respective specific B cells. However, the transcriptomic analysis performed in HBsAg- and HBcAg-specific B cells suggests additional roles of HBV-specific B cells beyond the production of antibodies. Lay summary Protection of viral infection necessitates the production of antibodies that are generated by specialized cells of the immune system called B cells. During chronic HBV infection, antibodies against the internal part of the virus (core or HBcAg) are detectable while the antibodies directed against the virus envelope (surface or HBsAg) are not present. Here we developed a method that allows us to directly visualize ex vivo the B cells specific for these two viral components, highlighting their differences and similarities, and showing how two components of the same virus can differently impact on the function of antiviral B cells.