Detailed investigation of B cell populations following vaccination and infection with severe acute respiratory syndrome coronavirus-2 during pregnancy.

Background: Pregnancy induces significant immunological adaptation, including shifts in the balance between B effector and B regulatory cells. However, the impact of SARS-CoV-2 infection or vaccination on B cell populations during pregnancy remains largely unexplored. Methods: Blood samples were collected from 139 women prior delivery and grouped according to the 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 determined, and B cell populations were analyzed by flow cytometry following short- and long-term stimulation with CpG ± CD40L and PMA/ionomycin or. Results: Serum levels of APRIL, IL-4, IL-6, TNF-α and sCD40L varied according to SARS-CoV-2 vaccination and infection status. Vaccination against SARS-CoV-2, and to a lesser extent infection with the virus, altered the frequency of various B cell populations, including plasma blasts, plasma cells and B memory cells. Patients infected with the virus exhibited increased levels of IL-10+ B cells, and decreased levels of IL-6+ B cells, in comparison to vaccinated women. In addition, the expression of CD40 was induced in B cells in response to infection. Conversely, the expression of PD-1, FasL and CD86 was enhanced by vaccination. Conclusion: SARS-CoV-2 infection and vaccination during pregnancy considerably shift the balance between pro- and anti-inflammatory B cell populations, and modified expression of costimulatory molecules. This highlights the need for further investigation into the long-term consequences of maternal SARS-CoV-2 immunity for both mothers and offspring.