Healthy intestinal mucosa contains T lymphocytes prone to secrete proinflammatory mediators only upon a strong <i>in vitro</i> stimuli.

<p>T lymphocytes (CD3 positive cells) producing cytokines were analyzed in intestinal biopsies of IBD and control paediatric subjects either at basal condition or after a brief <i>in vitro</i> mitogen stimulation. (<b>A</b>) Unstimulated CD3 positive cells infiltration and proportions of CD3 positive cells spontaneously producing TNF-α (<b>B</b>), and IFN-γ (<b>C</b>) in CD, UC and control biopsies are shown. Frequencies of CD3 positive cells producing TNF-α (<b>D and E</b>) and IFN-γ (<b>F and G</b>) after stimulation for 5 hours with PMA/Ionomycin are illustrated. Horizontal bars are the median values. The Mann-Whitney U test was applied to evaluate statistical significant differences.