Objective: To evaluate the production of interleukin-10 (IL-10) as well as levels of IgG and antinuclear antibodies (ANA) in systemic lupus erythematosus (SLE) patients and their first-degree relatives and spouses in Icelandic SLE multicase families.
Methods: IL-10 production was studied by enzyme-linked immunospot assay of freshly isolated peripheral blood mononuclear cells. Total IgG and ANA were also investigated. Subjects consisted of 23 SLE patients and 47 of their first-degree relatives in 9 Icelandic multicase families. Subjects were ethnically matched by a group of healthy controls. A separate study investigated 12 SLE patients (also from SLE multicase families) and their spouses and a matched group of healthy controls. A predefined protocol was used to obtain both clinical and laboratory data, including information about SLE and other autoimmune disorders.
Results: The SLE patients had a significantly higher number of IL-10-producing cells compared with both first-degree relatives and healthy controls (P = 0.0005 and P < 0.0001, respectively). First-degree relatives also had a significantly higher number of IL-10-producing cells compared with healthy controls (P = 0.01). This was also true for the spouses of SLE patients, who had a higher number of IL-10-producing cells compared with matched healthy controls (P = 0.02).
Conclusion: SLE patients and their first-degree relatives, as well as a limited number of healthy spouses of SLE patients, had increased numbers of spontaneous IL-10-producing cells. These data support the hypothesis that IL-10 production may be genetically determined, and may predispose one toward development of SLE. This has previously been suggested by studies of SLE patients and their relatives in another ethnic population, using another method for measuring IL-10 production. Although these data are based on a small number of observations, they suggest that not only genetic but also environmental factors may be of importance in determining IL-10 production, since the spouses of SLE patients also had an increased number of IL-10-producing cells.