Leukocyte immunophenotype of XLP patients 9 and 4. Percentages of CD3⁺ T lymphocytes, CD19⁺ B lymphocytes, CD56⁺ NK lymphocytes, CD3⁺CD56⁺ NK T cells, and CD4⁺CD3⁺ and CD8⁺CD3⁺ T regulatory subsets were determined by flow cytometry, as described in “Patients, materials, and methods.” Shaded area corresponds to the normal range (mean ± 2 SEM) of determinations performed simultaneously on 7 controls (asymptomatic adults with positive IgG anti-VCA serology).