Expanded CD8 T cells during acute infectious mononucleosis down-modulate CD3ζ and CD28 and up-regulate cell surface expression of T-cell activation markers.

(A) Lymphocyte expansion in subject AI-1 is primarily in the CD8 T-cell subset. (B) Expansion of CD3ζ− and CD28− CD8 T cells occurs in parallel in acute infectious mononucleosis. Initially, a larger proportion of expanded cells expressed CD38 and HLA-DR than down-modulated CD3ζ and CD28. In a post-convalescence sample 7 months later, the proportion of CD3ζ− and CD28− CD8 T cells remained elevated and encompassed approximately half of all CD8 T cells, whereas CD38 and HLA-DR expression returned to baseline values. Flow cytometry was performed on gated CD8−Cy5 bright lymphocytes.