OBJECTIVETo investigate the difference in the distribution, amount and morphology of immunocytes in fetal skin, normal adult skin and hypertrophic scar, and to probe into their roles in fetal scarless wound healing from the dermatological and immunological point of view.

METHODSSkin specimens obtained from 10 fetuses of induced labor (16 to 33 weeks gestation) due to incipient abortion, 7 adults, and 18 hypertrophic scars in different stages were collected for the detection of the expression and distribution of CD68 (the surface marker of macrophages) and CD3 (the surface marker of T-lymphocytes) with immunohistochemical assay.

RESULTSThe cells with positive expression of CD68 (CD68+ macrophages) in fetal skin [(5 +/- 6)/per 400 x visual field] were significantly lower than those in normal adult skin [(23 +/- 4) per/400 x visual field, P <0. 01], and they were obviously lower in normal skin than those in hypertrophic scar [(38 +/- 16)/per 400 x visual field, P < 0.01]. Along with their increase in gestational age, the CD68+ macrophages increased gradually. The cells increased in amount sharply during 24 - 28 gestational weeks, and then the increase slowed down after the 28th gestational week. The lymphocytes with CD3+ expression were not found in all the fetal stages, but were found in small amounts in adult skin [(24 +/- 8)/per 400 x visual field] which were mainly located in the epithelial basal lamina. But there were much more CD3+ lymphocytes [(69 +/- 25)/per 400 x visual field] in the HS, assembling usually in sheet form, and were chiefly distributed in dermal papillary layer around the small vessels in the shape of oversleeve. The cells were much more than those in normal adult skin (P <0.01) in terms of number and pigmentation intensity.

CONCLUSIONThe low content of CD68+ macrophages in fetal skin might be related to certain extent to the scarless skin wound healing. At the same time, the scarless skin wound healing in fetus could be related to the lack of CD3+ lymphocytes in fetal skin.