T cell clonal expansions in giant cell arteritis: disease or age related?

Purpose. To determine whether clonal expansions of T cells observed in Giant Cell Arteritis (GCA) are disease related or due to the age of the patient group. Methods. The expression of 19 T cell receptor (TCR) Vβ specificities were accurately determined by flow cytometry. Three groups were studied: (a) 25 healthy controls (20-35yrs, young controls), (b) 13 healthy controls (>50yrs, old controls), (c) 10 newly diagnosed GCA patients (ACR classification criteria). Blood samples were taken before or at most within 12hrs of starting corticosteroid therapy. Results. CD3+ lymphocytes were significantly reduced in GCA patients compared with both control groups. Within the CD3+ population, both old controls and patients showed increased CD4+ and decreased CD8+ frequencies compared with young controls. Young controls Old controls GCA pts Sig (t-test) CD3 68.7%* 66.3%t 47.1%*t *tp<0.01 CD4 63.1%*f 70.4%* 73.9%t *tp<0.01 CDS 25.3%*t 18.9%* 16.9%t *tp<0.01 Clonal expansions were defined as Vβ specificities expressed at a frequency greater than the mean + 3SD of the young control values. CD4+ expansions were seen in 60% of patients, and 61.8% of old controls. In the CD8+ subset, expansions were present in 60% of patients and 53.8% of old controls. Conclusions. CD3+ lymphocytes are reduced in GCA patients. The increase in CD4/CD8 ratio and frequency of clonal expansions are identical in patients and age matched controls. This suggests that alterations in the TCR repertoire in GCA are most likely age related rather than due to disease specific factors.