Jules Jean Baptiste Vincent Bordet (/bɔːrˈdeɪ/ bor-DAY, French: [ʒyl ʒɑ̃ batist vɛ̃sɑ̃ bɔʁdɛ]; 13 June 1870 – 6 April 1961) was a Belgian immunologist and microbiologist.

He graduated as Doctor of Medicine from the Free University of Brussels in 1892 and began his work at the Pasteur Institute in Paris in 1894, in the laboratory of Elie Metchnikoff, who had just discovered phagocytosis of bacteria by white blood cells, an expression of cellular immunity.

In 1895 Bordet made his discovery that the bacteriolytic effect of acquired specific antibody is significantly enhanced in vivo by the presence of innate serum components which he termed alexine (but which are now known as complement).

Four years later, in 1899, he described a similar destructive process involving complement, "hemolysis", in which foreign red blood cells are ruptured or "lysed" following exposure to immune serum.

[3] In this lecture, Bordet also concluded that bacteriophages, the bacteria-killing "invisible viruses" discovered by Felix d'Herelle did not exist and that bacteria destroyed themselves using a process of autolysis.