Immunohistowax processing, a new fixation and embedding method for light microscopy, which preserves antigen immunoreactivity and morphological structures: visualisation of dendritic cells in peripheral organs

Aims-To describe a new fixation and embedding method for tissue samples, im munohistowax processing, which preserves both morphology and antigen immuno reactivity, and to use this technique to investigate the role of dendritic cells in the immune response in peripheral tissues. Methods-This technique was used to stain a population of specialised antige n presenting cells (dendritic cells) that have the unique capacity to sensi tise naive T cells, and therefore to induce primary immune responses. The n umbers of dendritic cells in peripheral organs of mice either untreated or injected with live Escherichia coli were compared. Results-Numbers of dendritic cells were greatly decreased in heart, kidney, and intestine after the inoculation of bacteria. The numbers of dendritic cells in the lung did not seem to be affected by the injection of E coli. H owever, staining of lung sections revealed that some monocyte like cells ac quired morphological and phenotypic features of dendritic cells, and migrat ed into blood vessels. Conclusions-These observations suggest that the injection of bacteria induc es the activation of dendritic cells in peripheral organs, where they play the role of sentinels, and/or their movement into lymphoid organs, where T cell priming is likely to occur.