Objective: Daily exposure to food preservatives constitutes a major crisis to children especially during vaccination so; the aim of the study is to assess the effect of sodium nitrite on the immune responses against Rift Valley fever vaccine (RVFV) in Swiss mice.

Methods: Mice were divided into four equal groups: group 1 (control) was orally administrated with distilled water (2 ml/kg b. wt.); group 2 was orally administrated with the acceptable daily intake (ADI) of sodium nitrite 0.07 mg/kg b. wt. daily for 21 d, group 3 was vaccinated with inactivated RVFV two times and group 4 was orally given sodium nitrite and vaccinated as group 3. Blood samples were collected from all groups two weeks after booster vaccination. The leucocytic indices and the neutrophil-lymphocyte ratio (NLR) were determined to assess the cell-mediated immunity. The humoral immunity was evaluated using direct enzyme-linked immune-sorbent assay (ELISA) test and serum neutralization test (SNT).

Results: Sodium nitrite significantly increased the neutrophil index and the NLR whereas; it decreased the total leucocytic count and lymphocyte index in both non-vaccinated and vaccinated mice. Moreover, sodium nitrite significantly decreased both the IgG titer and the efficiency of vaccination through increasing the ED50 value.

Conclusion: Sodium nitrite existed an immune-suppressive effect on both cellular and humoral immune responses in mice.
Keywords: Sodium nitrite, Rift Valley fever, Immunity, Antibodies, Challenge