Immunohistochemistry of 'tertiary lymphoid follicles' in oral amalgam-associated lichenoid lesions

OBJECTIVES: To characterise lymphoid follicle-like aggregates incidentally found to occur in biopsies of oral lichenoid reactions (OLR) and to correlate the findings to hyperplastic tonsil follicles.
DESIGN: An immunocytochemical analysis of archival material.
SUBJECTS AND METHODS: In an arbitrarily selected period 1992–1994 with a total of 13 924 oral biopsies, 2407 cases were signed out as OLR or lichen planus. These were microscopically reviewed, with the purpose to retrieve all cases showing histologic changes resembling secondary lymphoid follicles.
RESULTS: 87 cases showed lymphoid follicle-like changes and 82 of these were in oral regions known to constitut-ively lack 'organised MALT'. Unexpectedly, all of the 82 were found retrospectively to be in close or direct contact with amalgam fillings. Immunocytochemically, using antibodies to B and T cells, macrophages, follicular dendritic cells and proliferation and apoptosis markers, the mucosal follicles stained similar to tonsillar secondary follicles. In several of an additional 11 OLR cases with histologic changes suggestive of primary follicles, we also found immunocytochemical evidence of such changes.
CONCLUSIONS: 'Tertiary lymphoid follicles' may occasionally develop in OLR at sites of the oral mucosa constitutively lacking organised lymphoid tissue. The microenvironment of the OLR T cell infiltrate may occasionally favour such follicle development and amalgam constituents may causally be involved in an unknown way.