Cytokine content in the membranes of activated Th1 and Th2 cell clones. Cytokine levels were determined by enzyme-linked immunosorbent assay in Th cell membranes. Th cells were activated by CD3 cross-linking for six hours before membrane preparation. The bars represent the mean ± standard deviation of six Th1 and six Th2 cell clones, and indicate the cytokine levels in the cell membranes from 2 × 105 cells. When a given cytokine was not detectable, it was assigned the value 0 for mean determination. *P < 0.05. IFN, interferon; IL, interleukin; ND, not detectable; Th, T-helper; TNF, tumour necrosis factor.