Immunohistochemical and immunoelectron microscopic localization of S-100 protein in the interdigitating reticulum cells of the human lymph node.

Lymph nodes of 5 cases with non-specific lymphadenitis and of 4 cases with dermatopathic lymphadenitis were examined by the peroxidase anti-peroxidase (PAP) method and by immunoelectron microscopy using monospecific antibody against nervous system specific S-100 protein. S-100 protein was detected in dendritic shaped cells of the thymus-dependent area of non-specific lymphadenitis. The paracortical area of dermatopathic lymphadenitis showed a marked accumulation of S-100 protein-containing dendritic shaped cells. Immunoelectron micrographs revealed that S-100 protein-containing dendritic shaped cells of both non-specific and dermatopathic lymphadenitis corresponded to interdigitating reticulum cells (IRC). The detection of S-100 protein in the nucleus and on the cytoplasmic and nuclear membrane suggested that IRCs themselves synthesized S-100 protein. S-100 protein is a very useful cell marker for the identification of IRC in the lymphoid tissue.