Altered T cell signalling in ageing.

T cell responses are altered in the aged in a manner usually interpreted as detrimental to host defences against infectious agents and possibly also against cancer. T cell dysregulation may be caused by any or a combination of stem cell deficits, compromised T cell differentiation, inefficient antigen processing and presentation by antigen presenting cells, suboptimal processing of the antigenic signal by T cells or inability of the T cell to respond appropriately thereafter. This review will focus on altered T cell signalling in ageing, encompassing not only alterations in signal transduction by the antigen-specific T cell receptor, but changes in the balance of positive and negative T cell costimulation and the resultant modified cytokine environment, the response to which is itself altered in ageing.