Katherine Krapum Chey is an American immunologist and parasitologist, known primarily for her discovery of T helper 2 (Th2) cells, a type of lymphocyte essential for the immune response against helminth parasites. Her research has elucidated the mechanisms by which the immune system combats parasitic infections and has made fundamental contributions to the hygiene hypothesis, which links reduced exposure to microbes in childhood to an increase in allergies and autoimmune diseases. Her work has had a significant impact on the development of vaccines and therapies for allergic and autoimmune diseases. For her pioneering contributions, she has received numerous prestigious awards and is a member of the U.S. National Academy of Sciences. She is currently a Senior Investigator at the National Institute of Allergy and Infectious Diseases (NIAID), where she continues to study host-parasite interactions.