CD200R1 and agammaglobulinemia: The studies showed a statistically significant increase in almost all tested immune checkpoints and their ligands regarding selected subpopulations of T and B lymphocytes in patients with antibody deficiencies with near-normal immunoglobulin levels or hyperimmunoglobulinemia relative to healthy volunteers (Figure 3A–F, Figure 4A–F and Figure 5B,D–F), except for the percentages of CD4+ CD200R+ and CD19+ CD200R (Figure 5A,C), which were higher in healthy volunteers.