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There is evidence for immunotoxicity of aflatoxin B1 (AFB 1 ) 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 AFB 1 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 AFB 1 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 AFB 1 on humoral immunity was assessed by measuring serum anti-keyhole limpet hemocyanin (KLH) IgM levels. Of the tissues examined, only the thymus weight of AFB 1 exposed mice decreased significantly compared to naïve mice; however, the decrease was not dose related and was also observed in the 0 AFB 1 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 AFB 1 . The number of CD4 + (helper T-cells), CD8 + (cytotoxic T-cells) and CD19 + (B-cells) decreased in spleens of AFB 1 aerosol exposed mice compared to naïve mice; however, the decrease was not dose-related and was also observed in the 0 AFB 1 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 AFB 1 compared to naïve mice, suggesting that AFB 1 did not effect antigen-specific antibody production. Based on the results of this study, a single AFB 1 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 AFB 1 -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 AFB 1 aerosol exposure. [ABSTRACT FROM AUTHOR]