Interestingly, long-term exposure to leptin, similar to the situation in obese individuals in whom elevated serum leptin levels are seen, significantly impairs integral parts of NK cell immune functions and decreases cell proliferation while short-time stimulation with leptin increases IFN-γ (interferon γ) secretion, CD69 activation marker expression, and cytotoxic lysis of tumor cells [43]. Here, LEP is linked to neoplasm.