Two conjugated linoleic acid (CLA) isomers, cis-9, trans-11 (CLAc9t11) and trans-10, cis-12 (CLAt10c12), reduce inflammation in a number of animal models, including collagen-induced arthritis (CA). However, little is known about the ability of individual CLA isomers to prevent autoimmune disease onset. Evidence that mixed isomer CLA drives T helper cell (Th) 1 responses suggests that CLA, or a specific isomer, exacerbates onset of Th1 autoimmune diseases. In two experiments, we examined if prior dietary exposure to CLAt10c12 (experiment 1) or CLAc9t11 (experiment 2) affected the incidence or severity of CA. DBA/1 mice were fed a semi purified diet with either 6% corn oil (CO, w/w), 5.75% CO plus 0.25% CLAt10c12, or 5.5% CO plus 0.5% CLAc9t11 prior to arthritis development. Arthritis incidence and severity, anti-collagen antibodies, paw cytokines, and hepatic fatty acids were measured. CLAt10c12 had no effect on arthritis incidence but increased arthritic severity (42%, P = 0.02); however, CLAc9t11 decreased arthritis incidence 39% compared to CO fed mice (P = 0.01), but had no effect on disease severity. CLAt10c12-induced increase in anti-collagen type II IgG antibodies may be a mechanism by which this isomer increased arthritic severity, and CLAc9t11-induced increase in Th2 paw cytokines (IL-4 and IL-10, P ≤ 0.04) may explain how CLAc9t11 reduced the arthritis incidence. While both isomers are well known to reduce inflammation in arthritic mice, these new data suggest isomer differences when fed prior to autoimmune disease.

Mixed‐isomer conjugated linoleic acid (CLA) and the individual isomers, trans‐10, cis‐12 (CLAt10c12) and cis‐9, trans‐11 (CLAc9t11), decrease severity of collagen‐induced arthritis (CA) when consumed after disease onset. Few studies have been conducted exploring the role of CLA in the prevention of autoimmune diseases. These studies suggest that isomer‐specific effects may be occurring; however, a direct comparison of CLAt10c12 and CLAc9t11 has yet to be conducted. A study to compare the ability of CLAt10c12 and CLAc9t11 to prevent CA and assess their effects on early inflammation was performed. DBA/1 mice were fed a semipurified diet containing 6% corn oil (CO), 5.5% CO and 0.5% CLAt10c12, or 5.5% CO and 0.5% CLAc9t11 (n = 27 per diet) starting three weeks before CA primary immunization. Effects on disease incidence and severity, anticollagen antibodies, plasma and paw cytokines, and hepatic fatty acids were measured. Arthritis incidence was reduced by a minimum of 34% in mice fed either CLA isomer compared to those fed CO diet (p = 0.06). In mice that did develop arthritis (n = 9–12 mice per treatment), CLAt10c12 reduced arthritic severity to a greater extent than CLAc9t11 and CO (p = 0.03). CLA isomer treatment attenuated the increased hepatic arachidonic acid (ARA; 20:4n‐6) observed with arthritis at one‐week postonset (p = 0.03), while no differences in anticollagen antibodies or cytokines were observed between dietary treatments. These results suggest that CLA isomers may be effective at preventing specific immune‐mediated inflammatory diseases, in part, through modulation of the ARA cascade.