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In page Polly Matzinger:

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The Self/Non-self Model proposed by Macfarlane Burnet and Frank Fenner in 1949 faced challenges in the late 1980s as immunologists recognized that T cells depend on antigen-presenting cells showcasing materials and sending co-stimulatory signals. Driven by the writings of Thomas Kuhn on paradigm shifts in science, Charles Janeway made a 1989 proposal that the innate immune system was the real gatekeeper of immune system responses. He also theorized that the innate immune system used ancient pattern-recognition receptors to make these decisions, recognizing a pathogen by its unchanging characteristics.[citation needed]