Oleander is the most potent immune stimulator on the planet as far as I am aware of (in European studies in 1986-87 it was shown to have six times the immune stimulating activity of the most potent patented immune stimulators at the time), so I would have to say that immune boosting is a very large part of its beneficial actions. It is also an outstanding immune stimulator and thus effective against autoimmune diseases that turn the body's immune system back on the body. In addition, the synergistic actions of the cardiac glycosides and other compounds it contains has specific actions against cancer cells to prevent them from multiplying and eliminate them by inducing and enhancing normal programmed cellular death via apoptosis and autophagy.
To get perhaps the best overall information about oleander this side of my ebook "Cancer's Natural Enemy", see the Oleander Series of articles at: