The Clonal Selection Theory, proposed by Frank Burnet in 1957, transformed our understanding of immunology by explaining how the immune system recognizes and responds to pathogens. The theory emphasizes antigen specificity, clonal expansion, immunological memory, self-nonself discrimination, and antibody diversity. It has informed vaccine development, monoclonal antibodies, cancer immunotherapy, and understanding of immune diseases.

The Iditarod Trail Sled Dog Race in Alaska is a long-distance race commemorating the 1925 serum run for diphtheria antigen, where sled dogs played pivotal roles. Balto, a Siberian Husky, is celebrated for leading the final leg, while Togo, Siberian Husky and part-wolf, covered the longest and most dangerous stretch. Despite Balto's initial recognition, Togo's contribution has gained appreciation over time. Both dogs are celebrated as heroes in sled dog racing, particularly in the context of the Iditarod.

In the late 1800s and early 1900s, intense debates in immunology centered on whether cell-mediated or humoral immunity was the primary defense against pathogens. German physician Paul Ehrlich spearheaded humoral immunity theories, while Russian immunologist Elie Metchnikoff championed cell-mediated immunity. Jules Bordet's research bridged the gap between the theories, leading to a comprehensive understanding of the immune system. These debates furthered the development of vaccines, such as the BCG vaccine for tuberculosis.