Isolation of multicellular complexes of follicular dendritic cells and lymphocytes: immunophenotypical characterization, electron microscopy and culture studies.

The morphological and phenotypical features of multicellular complexes formed by follicular dendritic cells and lymphocytes (FDC-LC) isolated from human hyperplastic tonsils and adenoids are described. FDC-LC obtained with this procedure were morphologically and immuno-phenotypically heterogeneous. In one type of FDC-LC, probably obtained from germinal centers, the lymphocytes exhibited ultrastructural features of centroblasts and centrocytes. In a second type, likely derived from follicular mantles, the enclosed lymphocytes were small in size and characterized by a condensed chromatin pattern. Similar heterogeneity was observed by immuno-phenotypical analysis, which revealed a prevalence of IgD+, CD3-, MT2+ small lymphocytes in a high proportion of FDC-LC. Both types of FDC-LC contained desmoplakin immunoreactivity in a typical punctate pattern corresponding to intercellular junctions when tested with a specific antibody. These findings confirm the importance of FDC in maintaining the follicular structure and also suggest that the different zones forming lymphoid follicles (mantle zone and germinal center) are formed by lymphocytes gathered in single "domains" by cytoplasmic processes of FDC. These domains have strong resistance to mechanical stress, such as that used in isolation procedures. FDC-LC have also been maintained as organized multicellular clusters for short periods (more than 48 h) in agarose gel cultures.