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T lymphocytes are thought to play an important role in the pathogenesis of Systemic Sclerosis (SSc). Perivascular accumulations of predominantly CD4+ T-lymphocytes are found at an early stage of scleroderma skin lesions. Moreover, soluble and membrane-bound adhesion molecules are elevated in SSc and may facilitate lymphocyte/endothelial cell contact. To assess the migration qualities of peripheral lymphocytes, we investigated the in vitro migration of SSc-lymphocytes through human endothelial cell monolayers.
Endothelial monolayers were formed by human umbilical vein endothelial cells (HUVEC) in their 3rd to 4th passage seeded on collagen gels and incubated over night. PBMC were prepared from 6 patients (5f, 1m, mean age 55 ± 6.5 yr.) fulfilling the ACR criteria for SSc and 6 healthy controls (HC; 5f, 1m, mean age 55 ± 7.11 yr.). Lymphocyte-migration was measured after one hour of incubation by fractionated harvest of non-adherent, bound, and migrated lymphocytes. Changes in the CD4/CD8 ratio and in the lymphocytic expression of activation markers (CD25, HLA-DR, CD69) and adhesion molecules (CD11a, CD49d) ex vivo, during and after migration were investigated by fluorocytometry.
The percentage of migrated SSc lymphocytes was increased in each single experiment (Fisher's exact test P < 0.03) when compared to HC (9.0 ± 4.4% vs 5.3 ± 2.9%). Compared to HC, the CD4/CD8 ratio was only slightly higher in SSc when detected ex vivo (2.71 ± 0.76 vs. 2.22 ± 0.54, P = n.s.), but increased after migration (3.00 ± 0.57 vs. 1.01 ± 0.38, P < 0.02), whereas the CD4/CD8 ratio in HC fell. The expression of lymphocytic activation markers and adhesion molecules was similar in SSc and HC ex vivo. Migrated SSc lymphocytes tended to express higher amounts of CD 25 and CD 49d, but this did not reach statistical significance in our small sample of patients.
Lymphocyte migration through a human endothelial monolayer is increased in SSc and is accompanied by an increase of the CD4/CD8 ratio. These data suggest that CD4+ SSc cells are more prone to migration than CD8+ cells and are in line with the paravascular accumulation of CD4+ lymphocytes.