Immunosuppression by surface-active material: lack of species specificity.

Surface-active material isolated from the lungs of both dogs and rats was tested for its ability to suppress the in vitro proliferative responses of dog, mouse, or human lymphocytes to a variety of immunologic stimuli. Both dog and rat surface-active material exerted a dose-dependent suppressive effect on the proliferative responses of each species of lymphocyte, regardless of the nature of the immune stimulus (mitogen, antigen, or alloantigen). The data indicated that surface-active material acts by directly inhibiting the responding lymphocyte and not by activating suppessor cells. The immunosuppression could not be attributed to lymphocyte cytotoxicity. Although the mechanism of this immunosuppressive action of surface-active material remains undefined, the present data clearly indicate that such activity is not species specific.