Tissue localization and retention of antigen in relation to the immune response.

Antigen persists for months or even years in lymphoid tissues of immune animals and this antigen is believed to participate in the induction and maintenance of B-cell memory as well as in the maintenance of serum antibody levels. In the present report we describe the phenomenon of antigen localization and long-term retention on mouse follicular dendritic cells (FDCs). The antigens used were injected in the hind footpads of immune mice and the popliteal lymph nodes were the lymphoid organs generally studied. In addition to presenting the morphological features of mouse FDCs, we report the results of a study of the mechanism of antigen migration from the site of initial localization in the lymph node subcapsular sinus to the regions of follicular retention in the cortex. The migration was followed by light and electron microscopy. The results support the concepts that immune complexes are trapped in the subcapsular sinus and are transported by a group of nonphagocytic cells to follicular regions. The mechanism of transport may involve either migration of pre-FDCs with a concomitant maturation into FDCs, or cell-to-cell transport utilizing dendritic cell processes and membrane fluidity; or a combination of the two mechanisms may be in operation.