Smoking has been associated with increased systemic lupus erythematosus (SLE) risk, but the biologic basis for this association is unknown. Our objective was to investigate whether women's smoking was positively associated with SLE-associated proinflammatory chemokines/cytokines (stem cell factor [SCF], B lymphocyte stimulator [BLyS], interferon-γ-inducible 10-kd protein [IP-10], and interferon-α); or negatively associated with antiinflammatory cytokine interleukin-10 (IL-10); and whether associations were modified by SLE-related autoantibody status.
The Nurses' Health Study (NHS, n = 121,700) and NHSII (n = 116,429) cohorts were begun in 1976 and 1989. In 1988-1990 (NHS) and 1996-1999 (NHSII), ~25% of participants donated blood samples. We identified 1,177 women without SLE with banked samples, and we tested by enzyme-linked immunoassay (ELISA) for chemokines/cytokines as well as anti-Sm, anti-Ro/SSA, anti-La/SSB, and anti-RNP. Antinuclear antibodies (ANAs) were detected by HEp-2 cell indirect immunofluorescence, and anti-double-stranded DNA antibodies and were assayed by ELISA. Smoking was assessed until blood draw. Separate tobit and linear regression analyses, adjusted for potential confounders, modeled associations between smoking and log-transformed chemokine/cytokine concentrations. Analyses were stratified by autoantibody status. Effect estimates were calculated as ratios of geometric means expressed as percentage differences.
Among the 15% of current/recent versus 85% of past/never smokers, BLyS levels were 8.7% higher (P < 0.01) and were 24% higher (P < 0.0001) among those who were ANA positive. Current/recent smokers had IL-10 concentrations 46% lower (P < 0.01) than past/never smokers; each 10 pack-years of smoking was associated with a 17% decrease in IL-10 level (P < 0.001). Smoking was not associated with IP-10 or SCF.
Elevated BLyS and lower IL-10 levels among current smokers, particularly among ANA-positive women, may be involved in SLE pathogenesis.