Histological increase in inflammatory infiltrate in sun-exposed skin of female subjects: the possible involvement of matrix metalloproteinase-1 produced by inflammatory infiltrate on collagen degradation

To investigate morphological changes occurring during cutaneous photoageing , a correlation between the number of infiltrating cells in the dermis and the degree of collagen damage was examined using sections from clinically n ormal chronically sun-exposed and sun-protected skin of Japanese female sub jects. Haematoxylin and eosin-stained sections from 134 sun-exposed (subjec ts aged 3-82 years) and :3 sun-protected (subjects aged 1-86 gears) areas d emonstrated a predominant lymphoid cell and to a lesser extent histiocyte i nfiltration, The mean +/- SD number of lymphoid cells and histiocytes in th e sun-exposed skin sections (427.0 +/- 192.2 and 147.8 +/- 83.3 cells/mm(2) , respectively) was significantly higher than in the sun-protected skin sec tions (292.6 +/- 98.3 and 125.9 +/- 59.0 cells/mm2, respectively) (P < 0.00 1 and P < 0.05, respectively), and the number of lymphoid cells in the sun- exposed skin sections increased significantly with age up to 50 years (r = 0.400, P < 0.001). Sun-exposed skin sections with severe collagen degenerat ion had a significantly higher number of lymphoid cells than those with sli ghtly degenerated collagen (mean 626.3 vs, 482.4 cells/mm(2), P < 0.01). Th e mean count of mast cells in sun-exposed skin was 202.0 cells/mm2; this di d not vary with the age of the subjects or the level of collagen damage. Im munohistochemical studies using 24 frozen sections identified most of the l ymphoid cells infiltrating sun-exposed skin as memory T lymphocytes (CD3+, CD4+ and CD45RO+). The number of cells which displayed immunoreactivity to matrix metalloproteinase (MMP)-1 in the sun-exposed skin sections was signi ficantly higher than in the sun-protected skin sections (mean 170.2 vs. 113 .6 cells/mm2, P < 0.05). Among these cells were observed CD3 and MMP-1 doub le-stained T lymphocytes, and T lymphocytes contacting MTP-1-positive cells . These morphological observations suggest that T lymphocytes infiltrating photodamaged skin may play a part in the degeneration and reduction of coll agen through MMP-1 activity.