The Sugar Coated Killer Cryptococcus neoformans: New Insights into Its Polysaccharide Capsule

Abstract

Aims: To analyze the polysaccharide property of capsular portion belongs to the incidiosa yeast, Cryptococcus neoformans. Discussion:  Cryptococcus neoformans is an encapsulated fungal pathogen that is acquired by human and animal hosts through inhalation of environmental infectious propagules and can stay dormant or minimally parasitized in the lung alveoli. It is lethal to the immunocompromised individuals, especially HIV (+), which can have caused cryptococcal meningitis. Morphologically, it is a round or oval-shaped yeast cell. The size of the organism is ∼2.5 μm without the capsular polysaccharide. The capsule is found immediately outside the cell wall and can vary in size from 1 to 50 μm, depending on the cell type, environment, and growth conditions. Capsule architecture is characterized by a complex Biochemical network connected to the cell wall and extending to variable distances into the extracellular space. The capsular portion of C. neoformans is always considered as the primary virulence factor. From the Biochemical properties, it is primarily composed of polysaccharides, most notably glucuronoxylomannan (GXM) and to a lesser extent, galactoxylomannan (GalXM), and mannoproteins. This elastic and thick, hydrophilic capsule is essential for the fungus's ability to cause disease, as it protects the yeast from the host's immune system by hindering phagocytosis and by modulating the phagosome environment. Cryptococcus cells from clinical samples typically have a much thicker capsule than those from the environmental samples or from culture medium. Fortunately, as a surprising findings, this capsular polysaccharide can be used as a simple methods of detection through the cryptococcal antigen in diagnostic tests. Conclusion: In C. neoformans, the components of the capsular network constitute the main fungal virulence factor as well as a precious element for simple detection.