Identification of Alkaline Phosphatase Positive Cells in Human Germinal Centres as Follicular Dendritic Cells

Abstract

Follicular dendritic cells (FDC) are exclusively found in germinal centers, where they form an extensive meshwork between the lymfoid cells. Many controversies exist about their origin. Ultrastructural studies on their ontogeny (1–3) suggest that FDC transform from fibroblastic reticulum cells. Marker studies have shown that FDC have antigens which are common to macrophages (4,5) and a monocyte-macrophage lineage has been suggested (6,7). Humphrey and Sundaram (8), however, excluded in their chimaera studies a bone marrow derivation of FDC. In a previous enzyme-cytochemical study on FDC isolated from human tonsils (9) we have shown that FDC have an enzyme pattern that is different from macrophages. At least a proportion of FDC is alkaline phosphatase-positive (AF⁺). Thus far it is unclear whether the alkaline phosphatase activity of FDC is an expression of a specialized activity of FDC or a “rudimental marker” of precursor cells of FDC. To study the nature and “in situ” localization of AF⁺ FDC we examined AF⁺ cells in germinal centers at the light and electron microscopical level.