The Lymph Node Niche.

Abstract SCI-51

Lymph nodes provide specialized stromal environments that support the maintenance and homeostasis of T and B lymphocyte populations and are also staging grounds for lymphocyte effector responses against pathogens and transformed cells. They serve as immune information hotspots by collecting lymph fluid from peripheral tissues, especially our external and internal epithelial body surfaces, thus displaying a condensed representation of foreign and self-antigens at these sites in addition to integrating innate alarm signals that report tissue damage or pathogen invasion. Naïve B and T cells constantly traffic through these environments via the blood stream and efferent lymphatic vessels, which allows for efficient matching of their antigen receptor repertoires with the regional antigenic landscape. Depending on the absence or presence of signs of a potential threat to the organism, the result may be either tolerance or immunity towards the origin of these antigens. The architecture of lymph nodes is optimized to facilitate the presentation of lymph-borne antigen in various forms and to guide naïve lymphocytes in their search for 'their' cognate antigen in the form in which they are able to 'see' it. It also facilitates the cellular crosstalk with other immune cell populations that shape and regulate an ensuing adaptive response if cognate antigen is encountered in an immunogenic context. Our conception of how these various tasks are accomplished has recently been enriched through new methodological approaches that include the dynamic in situ or in vivo visualization of cellular and molecular processes using modern microscopy technology. We will review some recent insights into the function of lymph nodes derived from these studies.