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 normal chronically sun-exposed and sun-protected skin of Japanese female subjects. Haematoxylin and eosin-stained sections from 134 sun-exposed (subjects aged 3-82 years) and :3 sun-protected (subjects aged 1-86 gears) areas demonstrated a predominant lymphoid cell and to a lesser extent histiocyte infiltration, The mean +/- SD number of lymphoid cells and histiocytes in the 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 sections (292.6 +/- 98.3 and 125.9 +/- 59.0 cells/mm2, respectively) (P < 0.001 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 degeneration had a significantly higher number of lymphoid cells than those with slightly degenerated collagen (mean 626.3 vs, 482.4 cells/mm(2), P < 0.01). The mean count of mast cells in sun-exposed skin was 202.0 cells/mm2; this did not vary with the age of the subjects or the level of collagen damage. Immunohistochemical studies using 24 frozen sections identified most of the lymphoid 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 significantly 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 double-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 collagen through MMP-1 activity.