PRF1 and neoplasm: In the presence of a tumor or virus, the Fab domains of IgG antibodies bind specifically to antigens expressed on the surface of the tumor or virus-infected target cells, while the Fc domain of IgG antibodies bind to NK cell CD16 Fc receptors, triggering the release of gamma interferon (IFN-γ), perforin, tumor necrosis factor alpha (TNF-α), granzyme B, interleukin-1 (IL-1), and granulocyte-macrophage colony-stimulating factor (GM-CSF) (6).