Lipopolysaccharide activation of murine splenocytes and splenic B cells increased the expression of aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator.

These studies characterized the profile of AhR and ARNT expression in primary splenocytes and purified splenic B cells after cellular activation with lipopolysaccharide (LPS). LPS treatment of mouse splenocytes markedly increased the magnitude of both AhR and ARNT steady state mRNA expression. AhR mRNA expression peaked at 8 hr post-LPS activation and was increased by approximately 5-fold compared with freshly isolated splenocytes (i.e., time 0). ARNT mRNA expression began to increase at 8 hr postactivation, peaked at approximately 48 hr and was increased by approximately 4-fold when compared with nonactivated splenocytes at time 0. Western blotting also demonstrated an increase in the relative magnitude of both the AhR and ARNT proteins in LPS activated splenocytes. Likewise, the presence of the AhR, ARNT and cytochrome P450IA1 (CYP1A1) proteins were also detected in purified primary splenic B cells, and the magnitude of protein expression was enhanced in LPS activated splenic B cells at 12 and 24 hr relative to time matched controls for each of these proteins. In summary, these findings suggest that on LPS activation the magnitude of AhR and ARNT mRNA and protein increases in both splenocytes and purified primary splenic B cells. Moreover, because the increase in the relative magnitude of CYP1A1 protein in response to LPS occurred in the absence of exogenous AhR ligand, these results suggest that B-cell activation is sufficient to induce AhR nuclear translocation and binding to dioxin-responsive elements in the promoter region of AhR-responsive genes.