The first consists of epithelial cells, endothelial cells and connective tissue cells including the reticular and follicular dendritic cells (FDC).

• 第一类包括上皮细胞、内皮细胞和结缔组织细胞（包括网状细胞和滤泡树突状细胞（folliculardendriticcells,FDC））。