A central role of CD40 ligand in the regulation of CD4(+) T-cell responses

Many of the costimulatory molecules thought to be essential for T-cell activation have now been identified. The CD40-CD40 ligand interaction is one such receptor/counter-receptor pair that has been shown to be important in B- and T-cell cognate interactions. Here Iqbal Grewal and Richard Flavell examine recent data from studies using gene knockout techniques that have helped provide a better understanding of CD40L's role in vivo, in regulation of the immune response.