Evaluation of Acute Immunotoxicity of Aerosolized Aflatoxin B₁ in Female C57BL/6N Mice

Abstract

There is evidence for immunotoxicity of aflatoxin B1 (AFB₁) in chronic animal feeding studies; however, little information is available as to the effects of inhalation exposure. This study evaluated the acute affects of aerosolized AFB₁ on systemic immune function of female C57BL/6N mice following a single aerosol exposure. Mice were exposed in nose-only inhalation tubes to 0, 2.86, 6.59 and 10 μg AFB₁ aerosol/L air for 90 minutes. A negative control group of untreated mice and a positive control group of cyclophosphamide-treated mice were included to account for day to day variation. Three days following exposure, mice were sacrificed and body, liver, lung, thymus and spleen weights, and complete blood counts and white blood cell differentials were measured. Splenocytes were isolated for flow cytometric analysis of CD4⁺ and CD8⁺ lymphocytes, CD19⁺ B-cells and natural killer cells (NK 1.1⁺). The effect of AFB₁ on humoral immunity was assessed by measuring serum anti-keyhole limpet hemocyanin (KLH) IgM levels. Of the tissues examined, only the thymus weight of AFB₁ exposed mice decreased significantly compared to naïve mice; however, the decrease was not dose related and was also observed in the 0 AFB₁ aerosol control group. A decrease in the mean white blood cell count of treated vs. naïve mice was observed at all dose levels but was clearly not dose related and was statistically significant only in the 0 and 2.86 μg/L groups. Red blood cell and platelet counts and white blood cell differentials were not significantly affected by AFB₁. The number of CD4⁺ (helper T-cells), CD8⁺ (cytotoxic T-cells) and CD19⁺ (B-cells) decreased in spleens of AFB₁ aerosol exposed mice compared to naïve mice; however, the decrease was not dose-related and was also observed in the 0 AFB₁ exposure group. Dose-related changes in the CD4⁺/CD8⁺ T-lymphocyte ratios were not observed. The IgM response to KLH was not significantly different in AFB₁ compared to naïve mice, suggesting that AFB₁ did not effect antigen-specific antibody production. Based on the results of this study, a single AFB₁ inhalation exposure up to 10 μg/L for 90 minutes (CxT = 900 μg ·min/L) did not significantly alter the immune parameters measured in this study. The aerosol vehicle (ethanol) and/or stress could have masked subtle AFB₁-dependent changes in thymus and spleen weights, and in splenic lymphocyte subpopulations. However, for other immunological parameters, such as the IgM response to KLH, there was clearly no significant effect of AFB₁ aerosol exposure.

Keywords :

• aflatoxin
• C57BL/6N mice
• AFB₁
• mycotoxin
• immunotoxicity