Demonstration of S-100 protein distribution in human lymphoid tissues by the avidin-biotin complex immunostaining method.

Immunoreactivity for S-100 protein was investigated immunohistochemically in a series of 49 fixed and paraffin-embedded normal, reactive, and neoplastic human lymphoid tissue specimens. The avidin-biotin complex immunoperoxidase method was used, with overnight (12-hour) incubation with a commercially available antiserum to S-100 protein. In addition, cryostat sections were tested with DRC 1 monoclonal antibody to dendritic reticulum cells (DRCs) in three cases and with OKT6 antibody to interdigitating reticulum cells (IRCs) in nine cases. All tissues, including lymph nodes, tonsils, adenoid, spleens, appendices, thymuses, and tissues containing nodular reactive lymphoid infiltrates, demonstrated a consistent immune staining pattern. A striking network composed of dendritic processes that showed finely granular S-100 protein immunoreactivity was observed in most of the follicular germinal centers; a similar dendritic pattern was observed in the follicular centers when the corresponding frozen sections were immunostained with DRC 1. In the extrafollicular areas, the S-100-positive cells topographically and morphologically resembled the IRCs that were demonstrated by OKT6 antibody in the corresponding frozen sections. The results seem to indicate that cells topographically and morphologically similar to IRCs and DRCs in human lymphoid tissues from different sites share immunoreactivity for S-100 protein. The present study confirms the unexpected presence of S-100 protein in dendritic cells of follicular germinal centers by a simple and currently available method.