SARS-CoV-2 vaccination and infection during pregnancy significantly shift pro/anti-inflammatory B cell populations

Pregnancy necessitates profound immunological adaptations, including a delicate balance between B effector and B regulatory cells to support fetal development while maintaining maternal immunity. However, the specific impact of SARS-CoV-2 infection or vaccination on these critical B cell populations during gestation remains largely uncharacterized. Understanding these immune shifts is vital, as dysregulated maternal immune responses can compromise both host defense and fetal outcomes, highlighting a significant gap in current knowledge regarding maternal-fetal immune health in the context of COVID-19.

Researchers collected blood samples from 139 pregnant women prior to delivery. Participants were categorized into five groups based on questionnaire responses and serology: controls (uninfected/unvaccinated), previously infected only, vaccinated only, both vaccinated and infected, and acutely SARS-CoV-2 infected (unvaccinated or vaccinated). Maternal serum cytokine levels were quantified using methods like ELISA, while B cell populations were extensively analyzed by flow cytometry following short- and long-term stimulation with CpG ± CD40L and PMA/ionomycin to assess functional responses and phenotypes.

Maternal serum levels of key cytokines, including APRIL, IL-4, IL-6, TNF-α, and sCD40L, were found to vary significantly based on SARS-CoV-2 vaccination and infection status. Vaccination against SARS-CoV-2, and to a lesser extent natural infection, distinctly altered the frequency of various B cell populations, specifically impacting plasma blasts, plasma cells, and B memory cells. Patients who experienced viral infection exhibited increased levels of IL-10+ B cells and decreased levels of IL-6+ B cells when compared to vaccinated women. Furthermore, the expression of CD40 was notably induced in B cells in response to infection. Conversely, vaccination was associated with enhanced expression of PD-1, FasL, and CD86 on B cells.

These findings highlight that both SARS-CoV-2 infection and vaccination during pregnancy considerably shift the balance between pro- and anti-inflammatory B cell populations, alongside modifying the expression of crucial costimulatory molecules.