For the purposes of the DAT:
Cytokines - a very broad category of proteins used in cell signaling. They aren't specific to just the immune system.
Interleukins - these are a specific group of cytokines that function in the immune system. Secreted primarily by helper T-cells to stimulate proliferation and differentiation of T-cells and B-cells. There are many different types of interleukins with more specific functions, but this knowledge is pretty detailed and likely beyond the scope of the DAT.
Interferons - secreted by cells invaded by viruses/pathogens that stimulate nearby cells to initiate defense mechanisms against the virus/pathogen.
Let me know if you need any further detail or explanation.