CD200R1 and agammaglobulinemia: Therefore, this study aimed to assess the percentage of T and B lymphocytes positively expressing three immune checkpoint pathways, namely PD-1/PD,-L1, CTLA-4/CD86, and CD200R/CD200, and the concentrations of their soluble forms in the serum of patients with antibody deficiencies with near-normal immunoglobulin levels or hyperimmunoglobulinemia compared to healthy volunteer controls.