LAUSR

The mitogen‐activated protein kinase p38 (MAPK) is implicated in the induction of immune responses by regulating the differentiation of T lymphocytes and production of cytokines. Our aim was to investigate p38MAPK phosphorylation in different stages of the natural history of hepatitis B virus (HBV) infection. Peripheral blood mononuclear cells (PBMCs) were isolated by Ficoll‐Hypaque density‐based centrifugation from 10 patients with HBeAg‐negative chronic hepatitis B [HBeAg(−) CHB;HBV‐DNA>2000IU/mL], eight patients with HBeAg‐negative chronic HBV infection [HBeAg(−) CI;undetectable HBV‐DNA] and 8 healthy controls (HCs). p38MAPK phosphorylation was assessed by phospho‐specific flow cytometry in PBMCs and cell subsets (CD3+,CD3−,CD56+,CD56−) after stimulation with cytokines (IL‐12+IL‐2 and IL‐12+IL‐18) or nonspecific stimuli [arsenite, phorbol 12‐myristate 13‐acetate (PMA) and ionomycin] at 0,30,60,120 and 240 minutes using p38 phospho‐specific conjugated antibodies. ΙFN‐γ was determined by ELISA in PBMCs culture supernatants after stimulation with rhIL‐2, rhIL‐12 and rhIL‐18, with and without pre‐treatment with the p38 MAPK inhibitor, SB203580. HBeAg(−) CI patients showed the highest expression of phosphor‐p38 MAPK in total PBMCs and subpopulations compared to HBeAg(−) CHB and HCs. A striking impairment in p38 phosphorylation was noted in CD56+ cells and in especially in NK cells (CD3‐CD56+). SB203580‐induced inhibition of p38MAPK phosphorylation was associated with suppression of IFN‐γ production in all groups. The universal lack of p38 MAPK activation in CD56+ and in particular in NK cells from HBeAg(−) CHB patients during viremia suggests a potential cell‐dependent implication of this pathway in the natural history of HBV infection.