Direct Assistance

Both B and T lymphocyte responses require support from specialized helper T lymphocytes, which mediate their effects via the cell-surface protein CD40. For B cells, this support involves direct interaction with helper T cells expressing CD40-ligand (CD40-L). For CD8+ T cells, such help has been assumed to depend on signals generated via CD40 on third-party antigen-presenting cells (APCs). Bourgeois et al. developed an in vivo system for priming CD8 responses in which CD40 was present on CD8+ T cells, but absent on APCs. As expected, CD4+ cells were required to supply help via CD40-L but could generate CD8+ T cell memory without the need for CD40 on APCs. The role for CD40 on CD8+ T cells, rather than on the APCs, indicates a direct form of help paralleling that used in B cell memory formation. C. Bourgeois, B. Rocha, C. Tanchot, A role for CD40 expression on CD8+ T cells in the generation of CD8+ T cell memory. Science 297, 2060-2063 (2002). [Abstract] [Full Text]