Opsonization of encapsulated Cryptococcus neoformans by specific anticapsular antibody

Area of Science:

• Immunology
• Microbiology
• Mycology

Background:

• Cryptococcus neoformans is an opportunistic fungal pathogen causing cryptococcosis.
• The yeast's capsule is a major virulence factor, influencing host immune responses.
• Opsonization, a process enhancing phagocytosis, is crucial for clearing microbial infections.

Purpose of the Study:

• To investigate the opsonic activity of antisera against Cryptococcus neoformans.
• To characterize the nature and specificity of these opsonins.
• To elucidate the mechanism of phagocytosis for encapsulated C. neoformans.

Main Methods:

• Preparation of antisera in rabbits against whole encapsulated C. neoformans cells and purified cryptococcal polysaccharide.
• Assessing opsonic activity through phagocytosis assays.
• Inhibition studies using free polysaccharide and 2-deoxy-D-glucose.
• Antibody characterization via gel filtration and ion-exchange chromatography.

Main Results:

• Antisera demonstrated significant opsonic activity for encapsulated C. neoformans.
• Opsonic activity was inhibited by free polysaccharide and showed type specificity across four serotypes.
• Opsonins were identified as immunoglobulin G (IgG) antibodies.
• Phagocytosis of opsonized encapsulated yeast was inhibited by 2-deoxy-D-glucose, unlike non-encapsulated yeast opsonized with normal serum.

Conclusions:

• Anticapsular antibodies are potent opsonins for encapsulated Cryptococcus neoformans.
• These IgG opsonins are type-specific and their activity is mediated by polysaccharide interactions.
• The mechanism of phagocytosis for encapsulated yeast opsonized with anticapsular antibodies involves 2-deoxy-D-glucose-sensitive pathways.