Susceptibility of congenitally athymic (nude) mice to sporotrichosis

Congenitally athymic (nu/nu) mice were found to be more susceptible to intravenous challenge with Sporothrix schenckii than their phenotypically normal (nu/+) littermates as measured by lethality and the number of viable yeast cells in the liver 7 days postinfection. Thymus reconstitution of nu/nu mice (nu/thy) conferred a significant degree of resistance to sporotrichosis. Immunization greatly enhanced the resistance of nu/thy and nu/+ mice, but unexpectedly increased the susceptibility of nu/nu mice. The susceptibility of nonimmunized nu/nu mice and the finding that thymus transplants augmented resistance to sporotrichosis suggest that T lymphocytes are critical to host defense.