A lymph node biopsy of a 6-year-old boy shows markedly decreased numbers of lymphocytes in the paracoical areas. Analysis of his peripheral blood leukocytes is likely to show normal to elevated numbers of which of the following CD cells?

The paracoex of the lymph node is the T cell-dependent area. Thus this patient is likely to lack circulating T cells. The T-cell markers will be low, but if any markers are elevated, it will be B-cell markers. CD19 is the only B cell-specific marker in the list. All the others are T cell markers. CD4 is found on helper T cells, while CD3 is found on all T cells.