A genetic approach to the aetiology of giant cell arteritis: depletion of the CD8+ T-lymphocyte subset in relatives of patients with polymyalgia rheumatica and arteritis temporalis.

Objective: To investigate the CD8+ T-cell concentrations in first degree relatives of patients with giant cell arteritis (GCA) in order to evaluate whether the low CD8+ T-cell values found in most patients with GCA are acquired or hereditary.

Methods: Probands were 5 patients with arteritis temporalis (TA) and 15 with polymyalgia rheumatica (PMR). Forty of 60 available relatives participated in the study. They were all interviewed concerning signs of previous illness. A blood sample screening was performed, including IgM-RF and ANA on Hep-2 cells. Age- and sex-matched controls consisted of 29 persons with no history of inflammatory or malignant diseases. Measurements of the T-lymphocyte subsets CD3+, CD4+ and CD8+ were made after Ficoll-Hypaque separation.

Results: Healthy relatives disclosed a significantly decreased CD8+ percentage in their peripheral blood compared with controls. The median CD8+% in relatives was 17% (C1 95% 15-20%) and in controls it was 23% (C1 95% 20-28%). Twelve relatives had a decreased concentration of CD8+ T-cells and 10 showed an elevated CD4+/CD8+ ratio. Two relatives had GCA and 3 had rheumatoid arthritis (RA). In one family 3 healthy siblings participated and showed extremely low CD8+ percentages (2.5%, 6.5%, 3.4%) and absolute values (0.042, 0.102, 0.035 x 10(9)/l)

Conclusion: TA, PMR and RA are frequently (12.5%) found in the first degree relatives of patients with GCA. The finding of extremely low CD8+ T-cell values in completely healthy relatives indicates that the CD8+ T-cell depletion seen in patients with GCA is a hereditary characteristic.