CD8 T cells with down-modulated CD3ζ have an activated/effector cell phenotype.

PBMC from representative samples from a normal donor (A) and from subjects AI-1 (B) and AI-2 (C) obtained during the acute infection (days 11 and 9, respectively) and convalescence (days 67 and 113, respectively) were stained for CD3ζ and CD20 and for CD3ζ, CD8 and CD28, HLA-DR, CD57, or perforin. The CD8 contour plots were obtained by gating on CD8−Cy5 bright cells. For the normal donor, most CD8 T cells are CD3ζ+ CD28+ HLA-DR- CD57−. In acute infection samples, the CD3ζ− CD8 T cells are mostly CD28− and HLA-DR+. In convalescence samples CD3ζ down-modulated CD8 T cells are mostly CD28–, HLA-DR+, CD57+, and perforin+. Quadrants were set using CD20+ B cells (y axis) as internal negative controls for background CD3ζ staining (x axis). Similar phenotypic profiles of CD3ζ− CD8 T cells were seen in samples obtained serially throughout the illnesses (not shown).