Human Peyer’s patches and intestinal lamina propria contain remarkably different numbers of dendritic cells positive for S-100 protein and macrophages positive for L1 antigen

The monocyte-derived cell lineages include classical phagocytic macrophages and various antigen-presenting dendritic cell types. The latter are poorly phagocytic but play an important role as accessory antigen-presenting cells in the induction of immune responses. S-100 protein (a formalin-resistant cytoplasmic antigen) is a useful marker for the specialized dendritic cells in the T-cell areas of lymphoid tissues, the so-called interdigitating cells or IDC [1], We have recently observed that reactive macrophages can be selectively labelled by staining for the formalin-resistant myelomonocytic LI antigen [2]. As a monoclonal antibody (Mac 387) to the latter marker is now available [3], we were able to perform paired staining for macrophages and putative IDC on formalin-fixed biopsy material from normal human distal ileum, including Peyer’s patches (PP).