Surfactant-like particles mediate tissue-specific functions in epithelial cells

Lipid-rich, unilamellar membranes appear to be relatively common structures lining the apical or 'exposed' surface of epithelial cells. They have now been described in the intestinal tract from the esophagus to the rectum and have been isolated from tissues, such as the stomach, the small bowel, the colon, and the bladder. The presence of a lining layer in the lungs has been known for some time, and its functions, structure, and metabolism have been extensively studied, as can be gleaned from the multitude of reports presented at this symposium. The 'other' surfactants, however, have attracted far less attention and have been investigated in detail in only a few reports. This paucity of information, when compared to the pulmonary system, is most likely due to the fact that a generalized function (sufficiency state) or disease (deficiency state) has not yet been recognized for either the intestinal or urinary forms of surfactant. It seems reasonable to assume that the role of the SLP will vary, at least in part, with the organ or tissue with which it is associated, although the widespread nature of the membrane assumes that some functions (e.g. protective) will be shared. Thus, pulmonary surfactant's primary function in the lung may be to reduce surface tension and prevent lung collapse; but it also plays a significant part in the lung's defenses against bacterial and/or chemical invasion. It is hoped that future studies will shed some light on the function of the various SLPs and lead to a better appreciation for their role in both maintaining a healthy environment and contributing to the proper functioning of their host tissues.