Recent studies suggest that T cells may have an important role in the pathogenesis of systemic sclerosis (SSc).¹ In patients with SSc, T cells exhibit the intermediate activation markers interleukin 2 receptor (IL2R) and HLA-DR in peripheral blood² and skin lesions.³ In peripheral blood there are increased levels of T cell cytokines, such as IL4^4,5 and IL17.⁶ T cell derived cytokines can cause fibrosis in tissues and small blood vessels in SSc. For instance, IL4 is a profibrotic cytokine. It induces collagen production in vitro and in vivo, whereas disruption of the IL4 receptor gene in animal models of SSc prevents fibrosis (reviewed by Sakkas and Platsoucas¹). T cells are also necessary for the production of antitopoisomerase autoantibodies in SSc.¹ Mononuclear cell infiltrates, consisting mainly of T cells and macrophages, appear in the skin early in the disease process.^7,8

We have recently found that the skin-infiltrating T cells in patients with SSc exhibit oligoclonal expansion and that the same T cell clone persists over time in individual patients.⁹ These findings suggest that T cells in skin lesions have been activated and expanded in response to an antigen. One antigen that is expressed on the cell surface early upon T cell activation is CD69.¹⁰ Therefore, we investigated the expression of CD69 in skin biopsy specimens from patients with SSc.

PATIENTS AND METHODS

RESULTS

All patients had antinuclear autoantibodies, and 11 patients had anti-DNA topoisomerase I autoantibodies. The mean modified Rodnan skin score was 28.6. (range 9–46.5). Inflammatory cells were detected in skin biopsy specimens of all patients. They were around small vessels and included CD3+, CD69+, and CD68+ cells (fig 1⇓). Table 1⇓ shows the degree of T cell and macrophage infiltration. The number of immunoreactive cells was increased in biopsy specimens from patients with SSc compared with controls. The mean number of CD3+ cells per high power field in SSc skin lesions was 59.9 (v 0.97 in controls, two tailed p = 0.02). Cells immunoreactive for CD69 were detected in all biopsy specimens. The mean number of CD69+ cells in SSc skin lesions was 18.9 (v 0.03 in controls, two tailed p = 0.006), whereas the mean number of CD68+ cells in SSc lesions was 77.2 (v 5.54 in controls, two tailed p<0.0001) (table 1⇓).

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Figure 1

 Immunoperoxidase staining of a skin lesion from a patient with SSc. Sequential sections were stained with anti-CD3, anti-CD69, anti-CD68 monoclonal antibody or with IgG1 (control).

There was a small decrease in the number of CD3+ and CD69+ cells as the disease duration increased. In patients with disease duration of <1 year, the mean number of CD3+ cells was 76.5, whereas the respective number was 20 in patients with disease duration of >5 years. However, there was no significant correlation between CD3 immunoreactivity and disease duration (Pearson correlation, r = −0.36, p = 0.08). Similarly, there was no correlation between the number of CD3+, CD69+, or CD68+ cells and the Rodnan skin score.

DISCUSSION

In this study mononuclear cell infiltrates were found in perivascular areas of skin lesions from patients with SSc. These infiltrates contained mainly CD3+ T cells and CD68+ macrophages, and were immunoreactive for the early activation antigen CD69. In sequential skin biopsy sections stained for CD3 and CD69 it appeared that CD69 was expressed on T cells.

Evidence of T cell activation has been reported previously in SSc skin lesions. For example, products of activated T cells, such as soluble IL2R, were found in suction skin blisters from patients with SSc.³ This study showed that T cells expressed CD69, one of the earliest known molecules expressed on the cell surface upon T cell activation.¹⁰ Activated T cells interact with other cells through cellular contact and through soluble mediators, the cytokines. The CD69 molecule is involved in contact cell interactions of T cells with other cells such as monocytes and fibroblasts¹² and is expected to influence fibroblast function in this way.

In a previous study we found that in SSc the skin-infiltrating T cells exhibit oligoclonal expansion.⁹ The oligoclonal expansion of T cells indicates an antigen driven T cell activation. In contrast, T cells activated non-specifically by cytokines exhibit polyclonal expansion. Taken together, these findings suggest that T cell activation in skin lesions from patients with SSc may take place in situ early in the disease process and it may be this T cell activation that initiates a series of cell-cell interactions that lead to tissue fibrosis and microvascular injury.

The numbers of CD3+ and CD69+ cells in SSc skin lesions were found to decrease over time, though not significantly, and the numbers of T cells did not correlate with the Rodnan skin score. This is not surprising given the complex natural history of SSc. At the onset of the disease there is an inflammatory phase—inflammation may appear before any histological evidence of fibrosis.⁸ Fibrosis dominates the skin lesion in a subsequent phase of the disease and, finally, may regress.¹³ In this initial inflammatory phase, T cells seem to have a central role. It is logical that in this inflammatory phase, treatments of patients with SSc should target T cells. Indeed, treatments directed against T cells in a few uncontrolled small studies support this concept. In these studies the proportion of patients whose skin improved was higher in patients with short disease duration¹⁴ than in those with long disease duration.¹⁵