Detection of circulating soluble CD28 in patients with systemic lupus erythematosus, primary Sjögren's syndrome and systemic sclerosis

Abstract

The aim of this study was to evaluate the presence and the role of the serum soluble costimulatory molecule CD28 in patients with systemic lupus erythematosus (SLE), primary Sjögren's syndrome (SS), and systemic sclerosis (SSc). Soluble CD28 concentration was determined by ELISA in 45 patients with SLE, 45 patients with primary SS, 30 patients with SSc, and 45 healthy subjects. We also evaluated CD28 mRNA expression by semiquantitative RT-PCR, and the biological activity of recombinant soluble CD28 on T lymphocyte activity. Concentrations of soluble CD28 were significantly higher in patients with SLE, primary SS and SSc than in healthy subjects. Soluble CD28 concentrations were higher in patients with systemic primary SS than in patients with glandular-limited primary SS. PCR analysis suggested that soluble CD28 resulted from the shedding of the membrane form. In vitro assay revealed that soluble CD28 inhibits the anti-CD3 mAb induced T cell proliferation. Soluble CD28, which modulates the proliferation of T lymphocytes, could be associated with disease severity in patients with autoimmune disease, especially primary SS. These results suggest that soluble CD28 could play an important role in the regulation of autoimmune diseases.

Fig. 1

Detection of soluble CD28 in human serum. Soluble CD28 was detected by ELISA in serum from systemic lupus erythematosus (SLE) (n = 45), primary Sjögren's syndrome (SS) (n = 45), and systemic sclerosis (SSc) (n = 30) patients, and healthy subjects (n = 45).

Fig. 2

CD28 mRNA expression in patients. The expression of CD28 transcripts was evaluated by RT-PCR in 5 patients (P1-P5) exhibiting the higher levels of soluble CD28 (irrespective of the pathology) and in 5 healthy subjects (representative result from only one subject are presented). RNA integrity and cDNA synthesis was verified by amplifying GAPDH mRNA.

Fig. 3

Soluble CD28 inhibits T cell proliferation. PBMC from healthy subjects were activated with anti-CD3 mAb (αCD3) without or with 0·1–10 µg/ml soluble recombiannt CD28 or 10 µg/ml soluble CD28-Fc. Control was proliferation induced by anti-CD3 plus anti-CD28 mAbs (αCD3 plus αCD28). Results are expressed in proliferation index (mean ± SD; n = 5).