Herpes simplex virus 2 (HSV-2) is a sexually transmitted infection that can cause painful, recurrent lesions in the genital skin and mucosa. HSV-2 initially infects genital epithelial cells before establishing latency in the dorsal root ganglion, from where it can reactivate and cause recurrent lesions at the site of infection. Symptom severity varies greatly among HSV-2+ individuals, ranging from asymptomatic infection to frequent symptomatic reactivation. The mechanisms behind the variability in viral control are incompletely understood, but it is appreciated that tissue-resident T cells at the site of infection are indispensable for local HSV-2 control. However, the roles of B cells—and the antibodies they produce—at the site of infection are less defined.
Drs. Emily Ford and Anton Sholukh from the Corey lab (Vaccine and Infectious Disease Division), along with colleagues from the University of Washington, sought to understand the role of local (or tissue-based) humoral immune responses in HSV-2 reactivation and viral control. In a recent Journal of Clinical Investigation article, the authors collected lesion biopsies during active HSV-2 outbreaks and at various time points post-lesion healing, along with biopsies from healthy control skin. They first looked for the presence of B cells by immunofluorescence (IF) staining, and found that B cells were more abundant during active lesion and early healing timepoints, and rarely seen in control or well-healed lesion sites. Additionally, they found some tissue-based B cells clustered with T cells, suggesting that B cells may have an important role in antigen presentation to anti-viral T cells. These findings demonstrate that tissue B cells are present in tissues involved by HSV-2 reactivation and are more abundant during active infection, suggesting that the humoral immune response may be important for HSV-2 control.
After establishing that B cells were present near HSV-2 lesions, the study next focused on whether tissue B cells produce antibody during HSV-2 lesion outbreaks. Although some B cells found near lesions expressed markers of antigen-inexperience—and were therefore likely unable to produce antibody— they found a subset of B cells expressing markers congruent with antibody secretion. The authors performed fluorescence in situ hybridization (FISH) to detect immunoglobulin (Ig) subtype IgG RNA, and found cells laden with abundant IgG transcripts present in lesion, but not control, samples. To confirm the presence of local antibody in biopsies, they stained for IgG protein by IF, and found that antibody production coincided with active lesions and that antibody was physically concentrated near active lesions but not in healed or control skin. These findings demonstrate that B cells of various developmental stages are concurrently present within HSV-2 lesions, suggesting that different B cell subsets may simultaneously carry out discrete roles such as antigen presentation to T cells and antibody production.
To determine if the antibody found at the lesion site was HSV-2-specific, the authors extracted antibody from both biopsies and serum and assayed for antibody specificity to HSV-2 or common, seroprevalent control antigens. HSV-2-specific antibody concentrations in tissue were dynamic, spiking at the time of active lesions, while antigen-specific antibodies in the serum remained stable over time. To explain this result, the authors hypothesize that antigen-specific antibody is either produced by locally infiltrating B cells. Together, these results suggest that the humoral immune response contributes to the control of HSV-2 reactivation and that tissue B cells increase production of HSV-2-specific antibody to control viral load and to facilitate virus clearance.
Tissue-resident T cells at the site of HSV-2 infection are known to be crucial to control HSV-2 reactivation, but this work demonstrates that B cells may be underappreciated for their roles in anti-HSV-2 immunity. B cells may both directly control HSV-2 spread through secreting antibody binding to virus and by presenting antigen to local T cells, activating these T cells to kill virally-infected cells. Going forward, Dr. Ford explained that their “two main future goals are to investigate the functional role that B cells play in inflammatory infiltrates during and after infection and to try to understand where these B cells are coming from, though of course both of those are really big questions. The work here definitely poses more questions than it answers, but we’re excited to keep digging.”
This work was supported by the National Institutes of Health and a Fred Hutchinson Cancer Research Center Vaccine and Infectious Diseases Division Initiative grant.
Fred Hutch/UW Cancer Consortium members Anna Wald, Jia Zhu, and Larry Corey contributed to this work.
Ford ES, Sholukh AM, Boytz R, Carmack SS, Klock A, Phasouk K, Shao D, Rossenkhan R, Edlefsen PT, Peng T, Johnston C, Wald A, Zhu J, Corey L. B cells, antibody-secreting cells, and virus-specific antibodies respond to herpes simplex virus 2 reactivation in skin. J Clin Invest. 2021;131(9):e142088. https://doi.org/10.1172/JCI142088.