Tissue histiocyte reactivity with CD31 is comparable to CD68 and CD163 in common skin lesions

CD31 is a standard immunostain for evaluating vascular lesions of the skin, but CD31 reactivity for histiocytes is reported in only a small variety of pathological conditions. CD68 and CD163 are well recognized stains for cutaneous histiocytic lesions. We compared immunostaining of CD31 within that of CD68 and CD163 in five cases each of cutaneous lesions containing histiocytes: healing biopsy site, granuloma annulare, xanthogranuloma, ruptured follicular cyst and sarcoidosis. Reactivity was graded on a scale of 0-3 for brightness of immunostaining. Immunoreactivity was seen in histiocytes in all specimens for CD31, CD68 and CD163. The average intensity of staining was 1.7-2.5 for CD31, 2.6-3 for CD68 and 2.9-3 for CD163. The staining was somewhat less for CD31 because the reactivity is localized on the cell surfaces, whereas CD68 and CD163 react with cell surfaces and cytoplasm. We conclude that histiocytes in cutaneous lesions stain for CD31 and the staining is comparable to, but less intense, than that seen with CD68 and CD163. Caution is suggested in interpretation of CD31 staining in skin specimens, as CD31 shows reactivity with histiocytes as well as endothelial cells.