2-Acetylaminofluorene suppresses immune response through the inhibition of nuclear factor-kappaB activation during the early stage of B cell development.

2-Acetylaminofluorene (AAF), an arylamide carcinogen, has been known to inhibit humoral and cell-mediated immune response by lipopolysaccharide (LPS). In the current study we demonstrate that AAF induced the down-regulation of protein kinase C (PKC) that is a key enzyme in the pathways leading to LPS-induced B-cell proliferation, while having no inhibitory effect on intracellular cAMP in spleen cells. Additionally, to identify the mechanism of action of AAF during B-cell development, we determined the effects of AAF on LPS-induced nuclear factor-kappaB (NF-kappaB) activation in 70Z/3 murine pre-B cells, CH12 murine mature B cells and S194 murine plasmacytoma cells. LPS-induced NF-kappaB activation, which is dependent on PKC, was inhibited by pretreatment with AAF for 2 h in the nuclei of 70Z/3 murine pre-B cells by detection of NF-kappaB specific DNA-protein binding. Conversely, AAF barely inhibited the constitutive NF-kappaB binding activity in mature B-cells, S194 and CH12. To confirm the effect of AAF on NF-kappaB activation, a chloramphenicol acetyl transferase (CAT) expression vector containing multiple copies of the NF-kappaB element (pCAT(kappaB)(3)) was transiently transfected into 70Z/3 or S194 cells, and assessed for inducible CAT activity. AAF treatment of 70Z/3 cells resulted in a significant inhibition of CAT activity induced by LPS. However, AAF exhibited no inhibitory effect on constitutive CAT activity in mature B cells, S194, indicating that AAF no longer has suppressive effects on the immune response in differentiated B cells. Taken together, these results suggest that AAF may act to suppress immune response by blocking the activation of PKC and nuclear expression of NF-kappaB at the early stage of B cell development.