Content of PD-1+ and PD-L1+ peripheral blood lymphocytes in individuals with pollen sensitization before and after allergen-specific immunotherapy

The available data on the contribution of the PD-1 and its ligands to immunoregulatory processes suggest their involvement into development of tolerance during immunotherapy. Currently, allergen-specific immunotherapy (ASIT) is the single treatment option that can influence the outcome of allergic diseases. Our purpose was to evaluate the PD-1/PD-L1 expression on the immune cells in patients with confirmed sensitization to plant pollen allergens in comparison with healthy controls before and after ASIT. The patients with bronchial asthma (BA) (n = 5, age 33.8±2.7), allergic rhinitis (AR) (n = 7, age 31.6±2.8), and healthy donors (n = 12, age 32.8±1.8) were included. Venous blood samples were obtained from the patients three times: before starting ASIT, upon completion of the ASIT course, and during the period of seasonal exacerbation. In patients with AR, the number of B lymphocytes was decreased, and the expression of PD-L1 by B lymphocytes increased after ASIT in comparison with donor parameters. At the same time, B lymphocyte counts were increased in BA patients before ASIT and returned to normal after ASIT. In AR, the CD8+PD-1+T lymphocyte count was reduced before ASIT, however, returning to normal values after ASIT was completed. Meanwhile, the reduced number of CD4+PD-1+T lymphocytes returned to normal only during the pollination season following ASIT. In BA patients, both before or after ASIT, PD-1 and PD-L1 expression on CD4+ and CD8+T lymphocytes did not differ from the donor parameters. The PD-1 expression in the T regulatory cells (Tregs) was decreased comparing with donors before ASIT in BA, and in the patients with AR, both before and after treatment. It was shown earlier that low PD-1 expression in the circulating CD4+ T cells is associated with high specific IgE concentrations. Thus, low PD-1 levels on CD4+ and CD8+T lymphocytes and regulatory T cells may indicate their functional disorders in allergic pathology. In summary, our results show a regulatory role of PD-1/PD-L1 axis in the immune response during ASIT and reflect differences in pathogenesis of allergic disorders, which are associated with imbalance of the cell activation and suppression. Further studies are required to establish the role of PD-1/PD-L1 interactions in the process of ASIT-induced modification of allergic responses.