Stromal cell regulation of homeostatic and inflammatory lymphoid organogenesis.

Secondary lymphoid organs function to increase the efficiency of interactions between rare, antigen-specific lymphocytes and antigen presenting cells, concentrating antigen and lymphocytes in a supportive environment that facilitates the initiation of an adaptive immune response. Homeostatic lymphoid tissue organogenesis proceeds via exquisitely controlled spatiotemporal interactions between haematopoietic lymphoid tissue inducer populations and multiple subsets of non-haematopoietic stromal cells. However, it is becoming clear that in a range of inflammatory contexts, ectopic or tertiary lymphoid tissues can develop inappropriately under pathological stress. Here we summarize the role of stromal cells in the development of homeostatic lymphoid tissue, and assess emerging evidence that suggests a critical role for stromal involvement in the tertiary lymphoid tissue development associated with chronic infections and inflammation.