Acid cysteine-proteinase inhibitor, a new characteristic of reticulum cells in human lymphoid secondary follicles.

Reactive lymph nodes, palatine tonsils and thyroid tissues infiltrated with reactive lymphatic tissue were studied for the presence of immunoreactive acid cysteine-proteinase inhibitor (ACPI). A positive reaction for ACPI was found in germinal centres in all the above tissue types. The morphology and distribution of the positive cells indicated immunoreactivity in the dendritic reticulum cells (DRC). A positive reaction was also found in starry sky cells when a strong starry sky reaction was present in germinal centres. ACPI-positive cells of dendritic appearance were also found outside the secondary follicles in tonsillar tissue from cases of chronic or recurrent tonsillitis, especially between the follicles and the crypt epithelium, in some lymph nodes exhibiting a strong follicular reactive hyperplasia and in thyroid tissue in one case of Hashimoto's thyroiditis. A close anatomical and morphological relationship is pointed out between ACPI reactive dendritic cells and epithelial tissue. This is especially true of the tonsillar crypt epithelium and adjacent lymphoid secondary follicles. The tonsillar crypt epithelium sometimes formed a loose, web-like structure with enmeshed lymphoid cells, even reminiscent of dendritic compartmentalization of lymphoid secondary follicles. The results suggest that ACPI-immunoreactivity of DRC could be a function of the outer membrane of dendritic processes, and thus could be in some way a parallel phenomenon to the morphological expression of the well-established function of DRC in capturing antigen and immune complexes.