An immunohistochemical study of endopeptidase-24.11 and aminopeptidase N in lymphoid tissues

Two cell surface peptidases, endopeptidase-24.11 and aminopeptidase N, thought to be involved in metabolizing regulatory peptides, have been immunohistochemically mapped in pig lymphoid organs using specific monoclonal and polyclonal antibodies. In tonsil, spleen, thymus and Peyer's patches, the endopeptidase-24.11 immunoreactivity exhibited a reticular pattern similar to that previously observed in lymph nodes, where this enzyme is much more abundant. Apart from this location in reticular cells, the only structures seen to express endopeptidase-24.11 were Hassall's corpuscles in the thymus, confirming their reticular cell origin. Aminopeptidase N exhibited a cellular distribution quite distinct from that of the endopeptidase. It was associated with cells scattered throughout the lymphoid organs studied, consistent with its localization in macrophages. In lymph nodes, some fibroblasts buried in trabeculae also stained for aminopeptidase, but this was not observed in spleen and thymus.