Expression of bcl-2 and Epstein-Barr virus LMP1 in lymphocytic interstitial pneumonia

Abstract

Background - Epstein-Barr virus (EBV) genome has been demonstrated in lung tissues of patients with lymphocytic interstitial pneumonia (LIP) but its role in the pathogenesis of this condition is unclear. In vitro studies have shown that EBV can immortalise and transform cells by upregulation of the cellular proto-oncogene, B cell leukaemia-2 (bcl-2), via the viral latent membrane protein, LMP1. The purpose of this study was to determine whether bcl-2 expression is upregulated in the lungs of patients with LIP and whether EBV LMP1 has a role in this bcl-2 expression. Methods - Immunohistochemical analysis using alkaline phosphatase antialkaline phosphatase (APAAP) was performed on formalin fixed, paraffin embedded lung tissues from 13 patients with LIP using anti-LMP1 and anti-bcl-2 monoclonal antibodies. Lung tissues from nine patients with idiopathic pulmonary fibrosis (IPF) and nine necropsy cases without pulmonary disease served as controls. LMP1 positivity was estimated as the number of LMP1 positive cells per unit area of lung tissue. Immunostaining for bcl-2 expression was assessed by a pictorial-based semiquantitative grading system. Results - Positive immunostaining for LMP1 was localised to airway epithelial cells of lung tissue. Ten out of 13 (77%) patients with LIP were positive for LMP1 compared with three of nine cases (33%) in each control group. LMP1 positivity of LIP cases was significantly greater than that of non-LIP cases: LIP versus IPF (mean difference, 95% confidence interval (CI)) 2.39 (1.54 to 3.24); LIP versus necropsy controls 2.62 (1.77 to 3.47). bcl-2 immunostaining was localised to lymphocytes within the alveolar septa and lymphoid aggregates of patients with LIP. The cumulative score for bcl-2 immunostaining was significantly higher in the lungs of patients with LIP than in those of patients with IPF and necropsy controls: LIP versus IPF and LIP versus necropsy controls (mean difference, 95% CI) 7.55 (7.18 to 7.92). Conclusions - These immunohistochemical studies have shown the presence of EBV LMP1 protein in airway epithelial cells and overexpression of the cellular bcl-2 protein in lymphoid cells of lung tissue in patients with LIP. These geographically distinct staining patterns of immunostaining suggest that the involvement of EBV LMP1 in the upregulation of cellular bcl-2 is more complex in LIP than was thought from previous in vitro observations. The respective roles of EBV LMP1 and bcl-2 in the pathogenesis of LIP require further studies.