Distinct resident and recirculating memory T cell subsets in non-lymphoid tissues

• Peripheral tissues contain a complex mixture of migrating and sessile memory T cells.
• CD103+CD8+ memory T cells are the best characterised type of tissue-resident memory T cells.
• Recirculating memory T cells (TRCM) may express peripheral as well as lymphoid homing molecules.
• Memory T cells present in peripheral tissues provide superior local immunity.

Antigen experienced or memory T cells make a critical contribution to immunity against infection. Many pathogens colonise non-lymphoid tissues and memory T cells in these compartments can deal with such localised infections. Emerging data show that there are at least two phenotypically distinct peripheral T cell subsets, one permanently resident and one recirculating between tissues and blood. A full appreciation of the T cells in the non-lymphoid memory pool and their relationship to those in the circulation is an important step in understanding how to generate and exploit effective peripheral immunity for the purpose of infection control.