CD4^lo cells.

CD4^lo cells form a distinct subpopulation of small T lymphocytes. Peripheral blood from an 85-year-old individual was stained with Cychrome–anti-CD4, FITC–anti-CD3, and PE–anti-CD14 monoclonal antibodies and analyzed by flow cytometry after gating the lymphocyte (A, inset, R1), monocyte (R2), and granulocyte (R3) populations. CD4^lo lymphocytes (arrows marked L) show low side scatter (SS; A); expression of CD3 similar to that of other CD4⁺ lymphocytes (B-C); and no expression of CD14 (D). Contrarily, monocytes (arrows marked M) with low CD4 expression (B) show higher SS (A); no CD3 (B); and strong CD14 expression (D). Panels B and D contain data from gates R1 and R2 (including both lymphocytes and monocytes), and panel C contains data from from gate R1 (lymphocytes only).