IFN-γ secreted by Th1 cells induces the upregulation of MHC II on the NK cell surface, allowing the NK cell to present endogenous viral antigens directly to naive CD4+ T cells

The NK cell's CD94:NKG2A heterodimer binds to HLA-E on a healthy cell, which sends a potent phosphorylation signal through ITAM motifs to activate the NK cell's lytic machinery

An NK cell identifies a tumor cell coated in IgG antibodies and binds to them using its CD16 (FcγRIII) receptor, initiating antibody-dependent cellular cytotoxicity (ADCC) 

A virally infected cell downregulates MHC I expression to evade CD8+ T cells; the absence of MHC I prevents the engagement of NK cell KIR (killer-cell Immunoglobulin-like receptors), removing inhibitory brakes and triggering degranulation

An NK cell recognizes MICA/B proteins on a stressed cell surface via its NKG2D receptor, which overrides inhibitory signals from MHC I molecules, leading to the release of perforins