Immunomodulation by pulmonary surfactant.

Canine pulmonary surfactant is recognized to modulate both T and B cell response in vitro. Because both responses involve cell proliferation, it has been suggested that surfactant interferes with the proliferation of lymphocytes. We herein report studies using human surfactant collected from amniotic fluid (HAFS). HAFS inhibited the proliferative response of human lymphocytes to antigen (PPD) and to allogeneic lymphocytes. Inhibition was linear within the dose range examined. Inhibition of the response to phytohemagglutinin was only evident when suboptimal doses of phytohemagglutinin were used. The effect of HAFS on the lysis of K562 human myeloid target cells by natural killer (NK) cells was also studied. Lysis in this system does not require proliferation. HAFS inhibited NK cell-induced lysis by 70% (250 micrograms HAFS per milliliter) to 95% (500 micrograms HAFS per milliliter). Inhibition was evident whether the cells were incubated with HAFS for 4 hours or for 18 hours. The NK suppressor activity was contained in the lipid fraction of HAFS, whereas the protein fraction revealed little activity. The washout experiments demonstrated that the action of HAFS was on NK cells and not on target cells. The immunomodulatory properties of surfactant affect NK cell activity and the proliferative response. Surfactant may protect the lungs from inappropriate immune reactions. Abnormalities of the lipid fraction of surfactant should be considered in studies of the mechanism of pulmonary diseases characterized by local pulmonary immune responses.