Nivalenol-induced changes in apoptosis-related genes expression and lymphocyte subsets in lymphoid tissues andmouse thymocytes primary cultures

Abstract

Nivalenol (NIV) is a trichothecene mycotoxin mainly produced by Fusarium nivale, and our previous study clarified that NIV is able to induce apoptosis in lymphoid tissues of mice in a dose dependent manner. In this study, NIV was orally administered to ICR mice at the dose of 15 mg/kg b.w., then thymus was taken from 30 min to 12 hours after inoculation (HAI), in order to investigate the expression of apoptosis-related genes (fas, c-fos, c-fun, p53, bcl-2 and c-myc) by RT-PCR method. The results indicated that c-fos and c-jun might play a critical role in NIV-induced thymocyte apoptosis because the levels of both c-fos and c-jun mRNAs were prominently elevated from 30 min and peaked 1 HAI prior to the development of apoptosis. In addition, the development of early apoptosis and changes in lymphocyte subsets were examined by FACS analysis in lymphoid tissues of BALB/c mice orally administered with 15 mg/kg b.w, of NIV, and also in thymocyte primary cultures treated with NIV at the dose levels of 0.25, 0.5 and 1μg/ml. The results indicated that NIV attacked Peyer's patches (PP) first and thymus most severely. In thymus, selective damage in CD4⁺CD8⁺ cells was observed at 12 and 24 HAI, following the peak of apoptosis at 9 HAI. CD4⁺ cells were clearly suppressed at 3 HAI in PP, at and after 9 HAI in mesenteric lymph nodes (ML), and from 3 to 12 HAI in spleen (SP), respectively. CD8⁺ cells were also suppressed at 24 HAI in ML and at 12 HAI in SP, respectively. As a result of in vitro experiment, the apoptotic cell index significantly increased in all groups at and after 3 hours after treatment (HAT) generally in a time-dependent manner. The number of CD4⁺CD8⁺ cells was prominently depleted in all groups in a time-dependent manner. These results also indicated that NIV directed affected thymocytes and induced apoptosis mainly in CD4⁺CD8⁺ cells. As to changes in B cell subsets, IgG⁺ cells significantly decreased from 3 to 12 HAI and all B cell subsets at 24 HAI in ML. In SP, IgM⁺ cells were suppressed at 9 HAI. On the other hand, in PP, following clear decrease in the numbers of pan-T and pan-B cells and viable cells at 3 HAI, all B cell subsets, especially IgA⁺ cells, showed a significant increase in their numbers at 9 HAI, and the numbers of IgA⁺ and IgM⁺ cells remained higher values than controls thereafter. Taken together, in the course of recovery from NIV-induced prominent damage in PP at 3 HAI, interaction of NIV with PP might result in in vivo stimulation of interleukin production at this site and result in increased proliferation and differentiation of IgA-secreting B cells at and after 9 HAI.