Alterations in fascin-expressing germinal center dendritic cells in neoplastic follicles of B-cell lymphomas.

Germinal center dendritic cells (GCDCs) have essential functions in retention of immune complexes within secondary follicles, B-lymphocyte antigenic stimulation, B-cell activation, homing of B-cells via adhesion molecules such as ICAM-1 and VCAM-1, and B-cell survival via apoptosis. The neoplastic cells of follicular lymphomas (FLs) are thought to derive from follicular B lymphocytes, but their relationship to GCDCs remains unclear. This study used immunohistochemical staining for fascin, a 55-kDa actin-bundling protein strongly expressed in GCDCs and their processes, to evaluate their distribution in neoplastic follicles. Forty-two cases of B-cell FL were evaluated, and immunoreactive staining for fascin was compared with six cases of Castleman's disease (CD) and six cases of follicular hyperplasia. FLs generally revealed decreased or absent fascin-staining GCDCs, suggesting loss of fascin expression by dendritic cells in neoplastic follicles compared with hyperplastic follicular centers. In some follicles, there was partial retention of dendritic architecture with islands of residual syncytial network. Interdigitating reticulum cells in the parafollicular regions revealed normal fascin expression with intense staining of dendritic processes. In contrast with FLs, cases of follicular hyperplasia revealed normal or increased fascin-positive follicular dendritic cells, and in cases of hyaline vascular CD, follicular dendritic cells revealed tight syncytial networks. These results suggest that GCDCs are deficient in neoplastic follicles, compared with benign reactive or hyperplastic follicles. This alterations in the germinal center microenvironment might explain the inability of FL cells to present antigen to T lymphocytes and to mount an effective antitumor immune response.