S-100 protein immunostaining in cells of dendritic morphology within reactive germinal centers by ABC immunoperoxidase method.

The "dendritic" and the "interdigitating" (IRC) reticulum cells are commonly reported to have different topographical distribution in the human lymphoid tissue and some peculiar cytochemical and immunohistochemical features. These include the detection of S-100 protein by PAP (peroxidase anti-peroxidase) method only in IRC located in the thymus-dependent areas. In 15 reactive lymphoid tissue specimens (11 lymph nodes, 3 tonsils, and 1 adenoid) the presence of S-100 protein was tested by ABC (avidin-biotin complex) immunoperoxidase method. IRC were constantly positive. Other positive cells were located within the follicular germinal centers; these immunostained cells appeared as a striking network composed of dendritic-shaped processes displaying a finely granular positivity for S-100 protein. It is suggested that by using this very sensitive technique, S-100 protein can also be detected in intrafollicular cells of dendritic morphology.