Identification of C-Type Lectin Receptors/Ligand Interactions Necessary for the Induction of Protection Against Cryptococcus neoformans Infections

The Wormley laboratory centers on the induction of protective immune responses against the opportunistic pathogen, Cryptococcus neoformans. C. neoformans is an encapsulated fungal organism responsible for 15 percent of global AIDS-related deaths each year. Cryptococcus can evade recognition of its conserved pathogen associated molecular patterns (PAMPs) through the expression of its carbohydrate capsule complex, which serves as its predominant virulence factor. However, receptor/ligand interaction(s) required for the induction of protection against Cryptococcus have yet to be elucidated. Therefore, the overall goal of this dissertation is to identify C-type lectin receptor (CLR)/ligand interaction(s) required for mediating protective immune responses against cryptococcosis.

Previous studies utilizing an overexpressing Zinc finger 2 (ZNF2) mutant of Cryptococcus, PGDP-ZNF2 or LW10, resulted in the induction of protection against an otherwise lethal challenge with wild-type (WT) C. neoformans. By comparing the host immune response to experimental pulmonary infection with the clinical isolate of C. neoformans, H99, to the attenuated LW10 mutant, we can determine the required signaling response necessary for the induction of protective host responses.

In order to evaluate the role of CLRs in recognition of Cryptococcus, we first analyzed the role of CARD9, an adaptor molecule that signals downstream of CLRs. CARD9 KO mice were significantly more susceptible to fungal infections and permitted increased fungal growth compared to WT mice. We then evaluated the role of macrophages from CARD9 deficient mice were unable to control fungal burden compared to WT macrophages. We therefore concluded that CARD9-mediated signaling is required for macrophage fungicidal activity against cryptococcal infections.

We then further characterized the role of CLR members Dectin-3 and Mincle receptors that are associated with CARD9 signaling. The Dectin-3 receptor was dispensable to cryptococcal infections, whereby Dectin-3 KO mice had comparable mortality rates, fungal burden, leukocyte infiltration, phagocytic uptake and killing capabilities compared to WT mice. Thus, we definitively demonstrated that Dectin-3 receptor is not required for the recognition and protection against Cryptococcus neoformans..

Lastly, we sought to evaluate the role of Mincle (Macrophage inducible c-type lectin receptor) in recognition of Cryptococcus. We determined that Mincle can recognize various morphotypes of Cryptococcus with a greater affinity to the filamentous LW10 strain. We then determined the role of Mincle in recognition during acute pulmonary infection with H99 as well as with LW10. Mincle proved to be dispensable during acute pulmonary infection; however, Mincle receptor enhanced protection to cryptococcosis. Identifying the CLR/ligand interaction required for the induction of protective immune responses can be potentially utilized for immunotherapeutic treatment and/or vaccine candidates.