Surface configuration of mesothelial cells in effusions. A comparative light microscopic and scanning electron microscopic study.

Surface configuration of mesothelial cells identified by light microscopy (LM) has been studied by scanning electron microscopy (SEM). It has been shown that mesothelial cells may have a variable SEM appearance. The surfaces of a small proportion of mesothelial cells are covered by regular microvilli (MV) and show openings of the pinocytotic vesicles. The surfaces of the majority of these cells are covered by vesicles or blebs. An intermediate population of mesothelial cells, i.e., cells displaying side-by-side blebs and MV, has also been observed. The latter cells no longer display pinocytotic vesicles. Occasional mesothelial cells have smooth surfaces. It has been shown by LM and transmission electron microscopy that cells with blebs are viable and capable of mitotic activity. It is concluded that mesothelial cells, detached from their epithelial setting, lose microvilli and pinocytotic vesicles and acquire surface blebs. The possible relationship between mesothelial cells and macrophages based on surface features has been discussed.