IFN-γ is produced primarily by CD3ζ− CD28− CD8 T cells in subjects with recent viral infection.

PBMC from a normal donor (A) and from early (day 11) (B) and convalescent (day 100) (C) samples from subject AI-2 were activated with CD3/PMA or nothing, cultured in the presence of Brefeldin A overnight, and stained for CD8, phenotypic markers, and permeabilized and stained for IFN-γ. Unstimulated cells did not produce IFN-γ. Similar results were found with samples from subject AI-1 (data not shown). Contour plots were obtained from analysis of gated CD8-Cy5 bright lymphocytes.