Neural architecture in lymphoid organs: Hard-wired antigen presenting cells and neurite networks in antigen entrance areas.

INTRODUCTION: Recently, we found abundant innervation of antigen presenting cells that were reached and enclosed by single neurites. These neurally hard-wired antigen presenting cells (wAPC) could be observed in the T-cell zone of superficial cervical lymph nodes of rats and other mammalians, including humans.

METHODS: As a consequence, we investigated lymph nodes at many different anatomical positions as well as all primary and secondary lymphoid organs (SLO) in rodents for a similar morphology of innervation regarding antigen presenting cells known in those tissues.

RESULTS: As a result, we confirmed wAPC in lymph nodes independent from their draining areas and anatomical positions but also in all other T-cell zones of lymphoid organs, like Peyer's patches, NALT and BALT, as well as in the thymic medulla. Other cells were innervated in a similar fashion but with seemingly missing antigen presenting capacity. Both types of innervated immune cells were observed as being also present in the dermis of the skin. Only in the spleen wAPC could not be detected. Beyond this systematic finding, we also found another regular phenomenon: a dense network of neurites that stained for neurofilament always in antigen entrance areas of lymphoid organs (subsinoidal layer of lymph nodes, subepithelial dome of Peyer's patches, subsinoidal layer of the splenic white pulp, margins of NALT and BALT). Lastly, also thymic epithelial cells (TEC) restricted to the corticomedullary junction of the thymus showed similar neurofilament staining.

CONCLUSIONS: Therefore, we propose much more hard-wired and probably afferent connections between lymphoid organs and the central nervous system than is hitherto known.