Antigen Processing Takes a New Direction

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Science  24 May 2013:
Vol. 340, Issue 6135, pp. 937-938
DOI: 10.1126/science.1239649

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T lymphocytes expressing αβ T cell receptors can be divided into those that express either CD8 or CD4 glycoproteins on their cell surface. Major histocompatibility complex (MHC) molecules on antigen-presenting cells present small fragments of antigenic proteins (epitopes) to T cells, and here again is a distinction: MHC class I (MHC-I) present to CD8+ T cells, whereas MHC class II (MHC-II) present to CD4+ T cells. Classical CD8+ T cells kill target cells, whereas CD4+ T cells exhibit effector and regulatory functions through cytokine secretion. On page 940 of this issue, Hansen et al. (1) challenge these paradigms of T cell antigen recognition and function and raise the possibility of achieving distinct T cell responses through the genetic manipulation of vaccine vectors.