REPORT Chemokines: role in inflammation and immune surveillance

Chemotactic migration of leucocytes largely depends on adhesive interaction with the substratum and recognition of a chemoattractant gradient. Both aspects, cell adhesion and chemotaxis, are regulated by members of the family of chemotactic cytokines (chemokines) comprising structurally related and secreted proteins of 67–127 amino acids in length. Breakdown in the control of leucocyte mobilisation contributes to chronic inflammatory diseases and, hence, interference with chemokine function is a promising approach for the development of novel anti-inflammatory medication. Chemokines target all types of leucocyte, including haematopoietic precursors, mature leucocytes of the innate immune system as well as naive, memory, and effector lymphocytes. The combinatorial diversity in respon-siveness to chemokines ensures proper tissue distribution of distinct leucocyte subsets under normal and inflammatory/ pathological conditions. Here, we discuss recent views on the role of chemokines in controlling tissue localisation of human memory T cells under steady state (non-inflamed) conditions. Emphasis is placed on a concept describing distinct subsets of memory T cells according to their primary residence in peripheral blood, secondary lymphoid tissues, or peripheral (extralymphoid) tissues. T he large majority of approximately 50 human chemo-kines fall into the group of either CXC or CC chemokines.1 2 In addition, there are two C chemokines, Ltn-a/XCL1 and Ltn-b/XCL2, in which two out of the four conserved Cys residues are missing, and a single CX3C chemokine, called fractalkine/CX3CL1, with three amino acids separating the two NH2 terminal Cys residues. Two nomenclature systems are used in the current literature, the traditional abbreviations dating back to the time of chemokine discovery, such as interleukin (IL)-8 and monocyte chemoattractant protein (MCP)-1, and a systema-tic nomenclature that combines structural motifs (CXC, CC, XC, CX3C) with L for ligand and the number of the respective gen