An impaired immune function linked to obesity has been shown in both human and animal studies. The purpose of this work was to analyse the hypothesis that PPARgamma1 participates in the inhibition of the immune response by affecting the DNA-binding ability of the NF-kappaB complex and whether the SREBP-1 expression can regulate PPARgamma1 expression in spleen. Diet-induced overweight rats showed higher PPARgamma1 (p < 0.05) and lower SREBP-I (p < 0.01) mRNA expression levels with an inhibition of the DNA-binding ability of NF-kappaB compared to control rats as determined by gel-shift analysis. On the other hand, energy restriction decreased SREBP-I (p < 0.01) mRNA expression with no differences in PPARgamma1 mRNA expression compared to non-restricted rats, which was accompanied by a restoration in the DNA-binding ability of NF-kappaB as shown by gel-shift analysis. These results suggest that PPAR-gamma1 may be involved in the altered immune response through changes in the activity of NF-kappaB. (C) 2003 Elsevier Inc. All rights reserved.