Peripolesis in alveolar sarcoidosis

We observed that in bronchoalveolar lavages (BAL) of patients with active sarcoidosis (SARC) a mononuclear cell infiltrate is present that often contains clusters consisting of lymphocytes adhering to a macrophage. In order to investigate what kind of cellular interactions are involved in such a process, cell suspensions obtained from BAL of patients with SARC or extrinsic allergic alveolitis (EAA) were cultured for 1 to 2 days, during which time lapse cinematography was applied. We were able to show that such clusters consist of lymphocytes gathered around a macrophage. This is known as peripolesis. Peripolesis, as observed in our BAL, could last for some minutes or for some hours during which time a number of lymphocytes were moving around a single alveolar macrophage, without losing contact with the macrophage. Short interactions were mostly observed in EAA, whereas SARC was characterized by long periods of lymphocyte-macrophage cooperation. We also found a correlation between the time-dependent peripolesis t > 30 min/t < 30 min and the CD4/CD8 ratio. Although the precise mechanisms of peripolesis are not well understood, some interactions between lymphocytes and macrophages have now become more comprehensive.