Effect of cytokines and anti-adhesion molecule antibodies on the adhesion of lymphocytic cells to human syncytiotrophoblast

We have previously shown that lymphocytic cells bind to cultured syncytiotrophoblast and that this may be important in the lymphocyte-mediated infection of trophoblast with the human immunodeficiency virus (HIV). Leukocyte-trophoblast adhesion may also have implications for normal trophoblast function. The following experiments were designed to characterize the adhesion systems that mediate the attachment of lymphocytic cells to trophoblast. Adhesion was assayed by labelling lymphocytic MOLT-4, clone 8 cells with the fluorescent marker, calcein-AM, and then incubating them with primary cultures of human syncytiotrophoblast. Adhesion was stimulated by pretreatment of the trophoblast cultures with several cytokines either alone or together. These included tumor necrosis factor-α (TNF-α), granulocyte/macrophage-colony stimulating factor (GM-CSF), interleukin-1β (IL-1β) and interferon-γ (IFN-γ). Stimulation was time- and dose-dependent. In contrast, preincubation of trophoblast cultures with anti-TNF-α antibodies for 2 days reduced MOLT adhesion by almost 50%. Preincubation with other anti-cytokine antibodies had no significant effect on adhesion. In other experiments, adhesion was measured in the presence of antibodies to known adhesion molecules. Adhesion was reduced by 50% in the presence of antibodies to α₄ integrin or β₁ integrin. When present together, these antibodies reduced adhesion by almost 85%. Incubation in the presence of antibodies to the very late activation antigen-4 (VLA-4; α₄β₁ integrin) counter-receptors, VCAM-1 and CS-1, was without effect. Adhesion was also unaffected by antibodies to LFA-1, ICAM-1, ICAM-2, LFA-2, or LFA-3. These results suggest that adhesion is mediated by an adhesion system consisting of lymphocyte VLA-4 (α₄β₁) and an as yet unidentified counter receptor on trophoblast.