Conjugated linoleic acid (CLA) seems to induce health effects in humans, but it has been suggested that it is the cis9,trans11 (c9,t11) CLA isomer that may be responsible for modulating the immune response⁽Reference Ramírez-Santana, Castellote and Castell¹⁾. The present study evaluates the effect of supplementing rats with an 80:20 mix of c9,t11 and t10,c12 CLA, respectively, on the capacity of generating polyclonal and antigen-specific immune responses.

A group of rats received CLA (n=20) during gestation and suckling through dams fed 1% CLA enriched diet and directly after weaning were fed same CLA dams diet until the adult age (15 weeks). Rats fed standard diet AIN-93G (n=20) were used as reference group. At 9-week-old of age all animals were immunized with ovalbumin (OVA) and 6 weeks later, spleens were removed and splenocytes were isolated and cultured. Cell proliferation was assayed by addition of polyclonal stimulus (PMA/Io, 250 ng/ml) for 72 h and determined by an ELISA method based on 5′-bromo-2′deoxyuridine cell incorporation. Supernatant IL-2 concentration after 24 h in same activation conditions were also quantified by ELISA. Specific proliferative response was evaluated by stimulating culture cells with OVA (10 μg/ml) for 96 h. Anti-OVA Ig production was determined in spleen culture supernatants and sera by ELISA, whereas spleen anti-OVA IgA-, IgG- and IgM-secreting cells (SC) were quantified by ELISPOT. Conventional ANOVA and post hoc comparisons were performed.

Splenocytes from animals which received CLA diet during all their life presented a lower (~10%) proliferative response after PMA/Io stimulation (P<0.05), which was also correlated to IL-2 cytokine reduction. The down-regulatory effect was not due to spleen cell viability loss. However, splenocytes from animals fed CLA diet presented a significant increase (~110%) in proliferative response after antigen (OVA)-stimulation compared to that of reference animals (P<0.05). OVA-immunized rats showed higher number of spleen anti-OVA IgG- and IgM-SC than IgA-SC. This pattern was not affected by long-term dietary CLA, although a tendency to increase the number of anti-OVA IgA-SC was exhibited. No differences were observed for anti-OVA Ig production between both dietary groups.

These results demonstrate that, although long-term supplementation with c9,t11 CLA seems not to affect humoral response, it is able to down-regulate unspecific lymphocyte proliferative function and to enhance specific proliferation by immunocompetent cells.