Figure 2.

Proliferative response of CD4⁺ naïve (triangles), CD27⁺ (squares) and CD27⁻ (circles) memory T cells to different concentrations of plastic-bound anti-CD3 immunoglobulin (in the absence of antigen-presenting cells) in the absence (white symbols) or presence (black symbols) of anti-CD28 immunoglobulin. The average of three individual experiments ± standard deviation is shown. CD27⁻ cells proliferate at a significantly higher rate (P < 0·01) than CD27⁺ cells without the addition of co-stimulation, at both 1 and 10 µg/ml concentrations of anti-CD3, in all individual experiments. c.p.m., counts per minute.