Immune response in dogs fed bixin

The immunomodulatory action of bixin is unknown. Female Beagle dogs (3 yr old) were fed 0, 5, 10 or 20 mg bixin (annatto seed extract; 1.6% bixin, <0.3% norbixin) (n = 13/group) for 16 wk. Blood was sampled on wk 0, 6 and 12 wk. All dogs were vaccinated with a polyvalent vaccine on wk 12 and 14, and blood taken on wk 16. Cutaneous hypersensitivity (DTH) response to saline, PHA, and vaccine was assessed on wk 12 and 16. Blood sampled was used to assess cell‐mediated and humoral immune response. In addition, C‐reactive protein concentrations and lipid peroxidation were determined in plasma. Dogs fed 5 or 10 mg bixin showed enhanced DTH response and B cell subpopulations as compared to control. Those fed 5 mg bixin also had higher concentrations of plasma IgG and IgM. The percent of total T cells was lower in dogs given 10 mg bixin compared to control. No similar immune response was observed in dogs fed 20 mg bixin except for enhanced against the vaccine DTH response. Bixin had no significant effect on mitogen‐induced lymphocyte response and NK cell cytotoxicity. All dietary doses, bixin suppressed plasma C‐reactive protein concentrations by 4 fold and lipid peroxidation by 2 fold; the higher bixin doses did not increase further these inhibition. Therefore, dietary bixin heightened cell‐mediated and humoral immune responses in dogs and showed anti‐inflammatory and antioxidative action; the optimal bixin dose was 5 mg.