Age- and sex-related patterns of serum interferon-alpha activity in lupus families.

OBJECTIVE

Interferon-alpha (IFNalpha) levels are elevated in many patients with systemic lupus erythematosus (SLE) and may play a primary role in its pathogenesis. The purpose of this study was to determine whether serum IFNalpha activity in SLE patients and their healthy first-degree relatives is highest in early adulthood, when the incidence of SLE is greatest.

METHODS

Serum samples from 315 SLE patients, 359 healthy first-degree relatives, and 141 healthy unrelated donors were measured for IFNalpha activity using a functional reporter cell assay. IFNalpha activity was analyzed in relation to age, and subgroups with high levels of IFNalpha activity were identified within the large data sets using a Mann-Whitney sliding window segmentation algorithm. The significance of each subgrouping was ranked by Kruskal-Wallis testing.

RESULTS

Age was inversely correlated with IFNalpha activity in female SLE patients (r = -0.20, P = 0.001) as well as their healthy female first-degree relatives (r = -0.16, P = 0.02). In male patients and their healthy male first-degree relatives, there was no significant overall correlation between age and serum IFNalpha activity. The segmentation algorithm revealed significantly increased IFNalpha activity between the ages of 12 and 22 years in female SLE patients and between the ages of 16 and 29 years in male SLE patients. Both male and female healthy first-degree relatives had significantly decreased IFNalpha activity after the age of 50 years.

CONCLUSION

Serum IFNalpha activity is higher in younger individuals in the SLE family cohorts, and this tendency is accentuated in affected individuals. This age-related pattern of IFNalpha activity may contribute to the increased incidence of SLE in early adulthood, and interestingly, males and females had similar age-related patterns of IFNalpha activity.