[Immuno-histological and-cytological examinations on distribution of newly reported co-stimulatory molecules in germinal center of human tonsils].

OBJECT: Co-stimulatory molecules are important for cell-cell interactions between immune cells, not only for cell activation, but for suppression. Several new co-stimulatory molecules have recently been discovered, and in this study we used immuno-histological and -cytological methods to investigate the distribution of such molecules in the germinal center of human tonsils.

MATERIALS AND METHODS: Tonsils surgically removed from patients with sleep apnea and habitual tonsillitis were examined. Expression of co-stimulatory molecules in immune cells was investigated immuno-histologically in frozen sections, and immuno-cytologically by flow cytometry.

RESULTS: PD-L1 was found to be expressed on both GCDCs (germinal center dendritic cells) and FDCs (follicular dendritic cells). ICOS and PD-1 were expressed on activated CD4 T cells located in the light zone of the germinal centers. 4-1BB was expressed on the FDCs, in human tonsils, but not on activated T cells.

CONCLUSION: GCDCs and FDCs are likely to function not only T cell activation but in negative regulation of T cells through PD-L1 expression. ICOS molecules contributing to positive signals, and PD-1 to negative signals were simultaneously expressed on a subset of activated T cells, suggesting that signal balance between ICOS and PD-1 is important for T-cell fate.