Dendritic cells (DC) recognize invading bacteria and rapidly activate T cell responses through a number of molecular events that remain incompletely understood. In September Nature Immunology, Francesca Granucci and colleagues from University of Milano-Bicocca, Milan, Italy show that early after bacterial stimulation dendritic cells provide activation signals by expression of interleukin 2 (IL-2)— a key signaling molecule that may greatly enhance both T and B cell responses.

Using specific chip microarrays, Granucci et al. performed a kinetic analysis of gene expression in immature mouse DCs stimulated at different time-points with live Gram-negative bacteria. They found that functional IL-2 mRNA — which gave rise to active IL-2 — was transiently up-regulated at early time-points after bacterial encounters. In contrast, other antigen presenting cells, for example macrophages, did not produce IL-2 following bacterial stimulation (Nat Immunol 2001, 2:882-888).

These findings suggest a key role for DCs in the activation...

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