The upregulation of LCK expression and suppression of IgM secretion are dependent on AHR activation within the first 24 h post B-cell activation. B cells were activated by coculture with CD40 ligand expressing L cells plus cytokines (IL-2, IL-6, and IL-10) on day 0. Following activation, B cells were treated with VH (0.02% DMSO), or TCDD (1 and 10 nM) on day 0, 1, 2, or 3 and cultured for a total of 7 days. (A) Percent LCK positive B cells measured by flow cytometry on day 7. (B) IgM concentration in supernatants as quantified by ELISA; (C) the number of IgM secreting cells as quantified by ELISPOT on day 7. Significant differences from VH control are indicated by *p<.05, **p<.01 by 1-way ANOVA following by Fisher’s LSD post hoc test. Results are presented as the normalized percentage compared with the VH group. “N” indicates the number of donors used in the study.