Renaissance poet and physician Girolamo Fracastoro (1478–1553) coined the neologism “syphilis” in the first poem that fictionalizes Columbus's voyage to the New World. Syphilis sive Morbus Gallicus (1530) captures, as this article shows, the bonds among poetic, philological, and medical discoveries as an unprecedented inquiry into the emerging discipline of immunology. A unique hinge between poetics and medicine as well as between ancient and modern languages, the poem takes the shape of a powerful philological intervention that is here called immunopoetics. An immunopoetic look at Syphilis not only underscores Fracastoro's crucial role in the history of immunitas, a juridical term that acquired, from the Renaissance on, an increasingly medical connotation and meaning. It also offers a new etymology for the word syphilis, which has hitherto remained obscure.