Low Blood Counts of Memory/Effector CD8 T Cells, Gamma/Delta T Cells, Memory B Cells and Plasmacytoid Dendritic Cells and High Counts of Th2 Cells in Systemic Sclerosis

Systemic sclerosis (SSc) is presumed to result from aberrant activation of autoreactive T cells. However, the exact pathogenesis of SSc is not known.

To contribute to the understanding of the immunopathology of systemic sclerosis (SSc), we compared blood counts of multiple lymphocyte subsets between 20 adult SSc patients not treated with immunomodulatory drugs and healthy controls. The patients had to fit entry criteria for SCOT trial (Scleroderma – Cyclophosphamide or Transplantation?, www.sclerodermatrial.org), i.e, 1. symptoms for no longer than 5 years (except for Raynaud's phenomenon), 2. diffuse scleroderma, and 3. either moderate lung involvement (forced vital capacity (FVC) or diffusion of carbon monoxide (DLCO) between 45 and 70% predicted) or moderate kidney involvement (history of hypertensive renal crisis, but normal renal function at study entry). Multiparameter flow cytometry was used for the determination of the lymphocyte subset counts.

Counts of the following subsets were significantly lower in the patients compared to the controls: total T cells (median 1316 vs 2088/ul, p=0.015), total CD8 T cells (273 vs 580/ul, p<0.001), central memory CD8 T cells (23 vs 87/ul, p<0.001), effector memory CD8 T cells (17 vs 39/ul, p=0.015), effector CD8 T cells (28 vs 68/ul, p=0.001), gamma/delta T cells (31 vs 77/ul, p<0.001), switched (IgM/DàIgG/A isotype switched) memory B cells (6 vs 26/ul, p<0.001), non-switched memory B cells (7 vs 17/ul, p=0.004), and plasmacytoid dendritic cells (2 vs 6/ul, p=0.002). Counts of Th2-biased (producing interleukin-4 upon polyclonal stimulation) CD4 as well as CD8 T cells were significantly higher in the patients compared to the controls (248 vs 139/ul for CD4, p=0.002, and 259 vs 164/ul for CD8, p<0.001).

Immunopathology of SSc is complex. Low blood counts of memory/effector CD8 T cells, gamma/delta T cells, memory B cells and plasmacytoid dendritic cells and Th2-biased T cells may play a role in the pathogenesis of SSc. However, cause and effect relations need to be established. Given previous reports of increased numbers of CD8 and gamma/delta T cells in the affected tissues of patients with systemic sclerosis and increased numbers of plasmacytoid dendritic cells in the affected tissues of patients with autoimmune diseases (compared to healthy individuals) (Prescott RJ et al: J Pathol 166 (1992) 255–63, Atamas SP et al: Arthritis Rheum 42 (1999) 1168–78, Giacomelli R et al: Arthritis Rheum 41 (1998) 327–34, Yurovski VV et al: J Immunol 153 (1994) 881–91, Nestle FO et al: J Exp Med 202 (2005) 35–43, Farkas L et al: Am J Pathol 159 (2001) 237–43), it is possible that the low blood counts of CD8 T cells, gamma/delta T cells and plasmacytoid dendritic cells result from redistribution of these cells from blood to affected tissues.

No relevant conflicts of interest to declare.