Chemokines as organizers of primary and secondary lymphoid organs.

Lymphoid organs represent highly specialized tissues enabling the development and activation of B and T lymphocytes. Contact between lymphoid and parenchymal cells in bone marrow and thymus is a prerequisite for proper development of B and T cells, respectively, while secondary lymphoid organs, such as spleen and lymph nodes are the places where B and T cells get into contact with antigen presenting cells in order to initiate an adaptive immune response. Recent evidence suggests that few constitutively produced chemokines are essentially required to allow for the correct positioning and interaction of lymphoid and non-lymphoid cells thus creating microenvironments for efficient development and activation of the immune system at multiple stages.