(A) TAP1 mRNA levels in primary B cells from two different donors are strikingly reduced after incubation with either B95.8 supernatant (labeled B95.8) or VFS (labeled VFS) in comparison with cells incubated with culture medium only (labeled RPMI). (B) The TAP1 mRNA level is not reduced with cell culture supernatant derived from the EBV-negative, IL-10–negative cell line DG7524 in comparison with reduced levels detected after treatment with B95.8 supernatant. (C) Cell culture medium (RPMI with 10% fetal calf serum) with appropriate dilutions of recombinant vIL-10 and hIL-10 from transiently transfected Cos7 cells causes the same reduction of TAP1 steady-state mRNA levels in primary B lymphocytes as does treatment with B95.8 shown in (A). B lymphocytes from two different donors were analyzed in parallel. (D) TAP1 mRNA steady-state level is reduced in tonsillar B cells after incubation with commerially available recombinant human IL-10 in a dose-dependent manner.