An immunohistochemical study of CD4, CD8, TIA-1 and CD56 subsets in inflammatory skin disease

Background: Antibodies to CD4, CD8, TIA‐1, and CD56 are available which perform well in formalin‐fixed and paraffin‐embedded tissue. While previous studies have investigated CD4 and CD8 subsets in inflammatory skin disease, few have specifically addressed TIA‐1 and CD56 reactivity in benign dermatoses. Given that CD8, TIA‐1, and CD56 are linked to aggressive lymphoproliferative disorders (i.e. subcutaneous panniculitic T‐cell lymphoma, natural killer (NK), and NK/T‐cell lymphomas), it would be important to determine their specificity for cutaneous hematologic malignancies. This investigation was undertaken to determine the frequency with which common, benign dermatoses express these four markers. We also sought to determine whether the ratio of CD4‐ to CD8‐positive cells could be used to distinguish among the dermatoses, especially the superficial and deep perivascular ones. Methods: Formalin‐fixed and paraffin‐embedded sections from a variety of common inflammatory dermatoses were stained with antibodies to CD4, CD8, TIA‐1, and CD56. Positive reactions were scored as a percentage of the entire mononuclear cell infiltrate. Results: All of the dermatoses represented in the study showed TIA‐1‐ and CD56‐positive lymphocyte subpopulations. On a case‐by‐case basis, the percentage of positive cells varied, and while all cases were positive for TIA‐1, many were completely negative for CD56. For TIA‐1, the percentage of positive cells ranged from 21 to 59%, and for CD56, from < 1 to 9%. The CD4:CD8 ratio ranged from 1.0 to 6.0 but was never less than 1.0. In addition to lymphocytes, TIA‐1 also stained polymorphonuclear leukocytes, eosinophils, and mast cells. Conclusion: TIA‐1‐ and CD56‐positive lymphocytes are common participants in routine inflammatory dermatoses, and therefore these markers are not specific for aggressive lymphoproliferative disorders. Using only immunohistochemical data, the ratio of CD4‐ to CD8‐positive lymphocytes could not be used reliably to separate the superficial and deep perivascular dermatoses from one another. Finally, mast cells are positive for TIA‐1 and are commonly seen in normal and inflamed skin, and thus TIA‐1 is not specific for cytotoxic T lymphocytes.