Inhibition of cluster formation and lymphocyte proliferation by anti-fibronectin antiserum

Dendritic cells (DC) confer concanavalin A responsiveness to accessory cell-depleted canine lymphocytes. DC-lymphocyte cluster formation is followed by blast transformation and proliferation of lymphocytes. We investigated whether fibronectin, which is known to be involved in cell:cell interactions, might also be involved in the interaction between canine DC and lymphocytes. The addition of rabbit anti-dog fibronectin antiserum to concanavalin A-stimulated peripheral blood mononuclear cells decreased cluster formation and reduced 3H-thymidine incorporation by 57-70%. Similarly, when cell fractions, enriched for DC, were pretreated with anti-fibronectin antiserum before being added back to accessory cell-depleted lymphocytes, cluster formation was reduced and lymphocyte proliferation after concanavalin A stimulation decreased by 18-46% as measured by 3H-thymidine uptake. Ferritin-conjugated anti-fibronectin antibody was bound to the surface of DC, primarily at the dendritic processes. We conclude that fibronectin, located on the surface of canine DC, participates in the accessory cell function of these cells.