CD3ζ is downmodulated in circulating lymphocytes from most HIV-infected donors. (A) The isotype-matched control antibody histogram is subtracted from the CD3ζ histogram (shaded) to obtain the number of ζ⁺ cells. In normal donor P14 and asymptomatic healthy HIV-infected subject 6159, the number of ζ-staining cells is comparable with the number of cells staining for CD3. However, in donor no. 214, who has oral hairy leukoplakia and thrush, CD3ζ expression is downmodulated. (B) CD3ζ staining for PBLs from 28 HIV-seropositive donors, graphed in order of declining CD4 counts. The dashed lines represent the normal range (C). (D) The percent of T cells that do not stain for ζ increases as the CD4 count falls. (E) CD3ζ downmodulation correlates with CDC disease stage. The ratio for stage A donors, 0.80 ± 0.14, is significantly lower than that of HIV-seronegative healthy donors (*P < .00001) but significantly higher than that of symptomatic stage B donors 0.55 ± 0.09 (**P < .001).