Figure 1. Hypothetical representation of the steps involved in recruitment, activation, and expansion of NK cells by HEp2- I B_(S32AS36A) cells. NFB knock-down HEp2 tumor cells, by producing large amounts of chemokines MCP-1 and RANTES, recruit NK cells. Due to a decrease in inhibitory signals—provided, for instance, by inhibitory MHC Class I antigens, IL-6 cytokine, and VEGF—NK cells remain viable and increase their functional activation at the site of pathology. Increased survival, in addition to augmented proliferation, results in significant expansion of the NK cells.