T11TS immunotherapy augments microglial and lymphocyte protective immune responses against Cryptococcus neoformans in the brain

Cryptococcus neoformans, the encapsulated yeast acquired through inhalation, remains localized in lungs, but harbours the CNS in immunocompromised individuals. Several treatment regimes have failed combating this disease totally, but long-term usage of drugs leads to organ damage. As T11-target structure (T11TS) has documented profound immune potentiation, we aimed to investigate the role of microglia, pivotal immune cells of brain in ameliorating cryptococcosis, with T11TS immunotherapy. Murine model with C neoformans infection was prepared by intraperitoneal injection and the brains of rats examined 7 days post-infections for histopathology by PAS and Alcian blue staining corroborated with organ fungal burden evidencing restorative T11TS action on Cryptococcal meningitis. Immunotherapy with three doses of T11TS, a CD2 ligand, in C neoformans infected rats, upregulates toll-like receptors 2, -4 and -9 of microglia, indicating increased phagocytosis of the fungus. Flowcytometric analysis revealed increased numbers of T11TS treated brain infiltrating CD4⁺ and CD8⁺ T-lymphocytes along with increased MHC I and MHC II on microglia, activating the infiltrating lymphocytes aiding the killing mechanism. Present study also indicated that T11TS increased production of Th1 inflammatory cytokines conducive to fungal elimination while the inhibitory Th2 cytokines were dampened. This preclinical study is first of its kind to show that T11TS effected profound immune stimulation of microglial activity of C neoformans infected rats eradicating residual fungal burden from the brain and can be a useful therapeutic strategy in fighting against this deadly disease.

Unraveling the novel structure and biosynthetic pathway of O-linked glycans in the Golgi apparatus of the human pathogenic yeast Cryptococcus neoformans

Cryptococcus neoformans is an encapsulated basidiomycete causing cryptococcosis in immunocompromised humans. The cell surface mannoproteins of C. neoformans were reported to stimulate the host T-cell response and to be involved in fungal pathogenicity; however, their O-glycan structure is uncharacterized. In this study, we performed a detailed structural analysis of the O-glycans attached to cryptococcal mannoproteins using HPLC combined with exoglycosidase treatment and showed that the major C. neoformans O-glycans were short manno-oligosaccharides that were connected mostly by α1,2-linkages but connected by an α1,6-linkage at the third mannose residue. Comparison of the O-glycan profiles from wild-type and uxs1Δ mutant strains strongly supports the presence of minor O-glycans carrying a xylose residue. Further analyses of C. neoformans mutant strains identified three mannosyltransferase genes involved in O-glycan extensions in the Golgi. C. neoformans KTR3, the only homolog of the Saccharomyces cerevisiae KRE2/MNT1 family genes, was shown to encode an α1,2-mannosyltransferase responsible for the addition of the second mannose residue via an α1,2-linkage to the major O-glycans. C. neoformans HOC1 and HOC3, homologs of the Saccharomyces cerevisiae OCH1 family genes, were shown to encode α1,6-mannosyltransferases that can transfer the third mannose residue, via an α1,6-linkage, to minor O-glycans containing xylose and to major O-glycans without xylose, respectively. Moreover, the C. neoformans ktr3Δ mutant strain, which displayed increased sensitivity to SDS, high salt, and high temperature, showed attenuated virulence in a mouse model of cryptococcosis, suggesting that the extended structure of O-glycans is required for cell integrity and full pathogenicity of C. neoformans.