Disturbances in the B-cell component of immune system and associated immune alterations in post-COVID patients

There is only limited data on B-cell response in post-COVID patients despite its importance in studying the post-infection immunity. The present study aimed to investigate the features of the B-cell response in post-COVID patients, focusing on various B cell phenotypes. Along with the standard immunogram, the following cell phenotypes were examined: common B cells (CD45⁺, CD3^-, CD19⁺); common memory cells (CD45⁺, CD3^-, CD19⁺, CD27⁺); common non-memory cells (CD45⁺, CD3^-, CD19⁺, CD5⁺); B1 memory cells (CD45⁺, CD3^-, CD19⁺, CD5⁺, CD27⁺); B2 memory cells (CD45⁺, CD3^-, CD19⁺, CD5^-, CD27⁺); B1 non-memory cells (CD45⁺, CD3^-, CD19⁺, CD5⁺, CD27^-); and B2 non-memory cells (CD45⁺, CD3^-, CD19⁺, CD5^-, CD27^-). The study revealed a sharp increase in B1 memory cells in 15.3% of post-COVID patients with impaired levels of B1 memory cells. This increase was accompanied by elevated levels of total B memory cells, B1 total lymphocytes (mainly, B1 memory cells), total T lymphocytes, and total IgA. By contrast, the patients with impaired B1 memory cells exhibited a sharp decrease in plasma cells, B2 lymphocytes (both memory and non-memory cells), natural killer cells, T regulatory cells, early activation T cells (CD25⁺), and C3a complement fragment. These findings suggest a unique immune system disorder characterized by dysregulated B lymphocyte switching from IgM to IgG and IgA synthesis, thus resulting in marked decrease in B2 lymphocyte subpopulations. This disorder may be associated with reduced T regulatory lymphocytes and early activation of T lymphocytes responsible for regulating B lymphocyte differentiation. Furthermore, the patients also exhibited reduced hemoglobin and platelet parameters, thus, potentially, contributing to hypoxia and blood clotting abnormalities. Thus, the phenotype identification of these immune system disorders in post-COVID patients requires non-standard approaches to assessing immune status, thus compicating clinical examination, but highlighting the need for immunocorrective therapies. These findings contribute to better understanding of post-COVID immune system disorders and require further investigation into the underlying causal factors.