Therefore, the purpose of this publication was a comparative analysis of selected parameters of the immune system, with particular emphasis on the role of immune checkpoints and their ligands (PD-1/PD-L1, CTLA-4/CD86, and CD200R/CD200) in the course of patients with CLL (representing a group of with SID) and CVID (representing a group with PID) in the context of EBV reactivation. The gene discussed is CD200; the disease is B-cell chronic lymphocytic leukemia.