T cells

Interactions between CD40 and CD40 ligand (CD40L) play a major role in direct CD4⁺ T cell–B cell collaboration, but the influence on CD8⁺ T cells — through the antigen-presenting cells (APCs) — has been assumed to be indirect. In September 20 Science, Christine Bourgeois and colleagues at INSERM U345, Institut Necker, Paris, France, show that, like B cells, CD8⁺ T cells receive CD4 help directly through CD40 and this interaction is fundamental for CD8⁺ T cell memory generation (Science, 297:2060-2063, September 20, 2002).

Bourgeois et al. used mice that had independent CD8⁺ T cells and CD4⁺ T cells, and genetically manipulated APCs. They observed that generation of memory CD8⁺ T cells displaying an enhanced capacity for cell division and cytokine secretion required CD4 help but not CD40 expression by APCs. In addition, they showed that activated CD4⁺ and...