Structure and biological activities of acapsular Cryptococcus neoformans 602 complemented with the CAP64 gene

Area of Science:

• Mycology
• Immunology
• Infectious Diseases

Background:

• The extracellular polysaccharide capsule is a key virulence factor in Cryptococcus neoformans.
• Strain 602, an acapsular clinical isolate, has been extensively used in virulence studies.
• Previous comparisons of strain 602 used genetically unrelated strains due to lack of a wild-type equivalent.

Purpose of the Study:

• To create an encapsulated version of the acapsular strain 602.
• To investigate the role of the capsule in the virulence and biological activities of strain 602.
• To determine the serotype origin of strain 602.

Main Methods:

• Transformation of acapsular strain 602 with the CAP64 gene from a serotype D strain.
• Serological tests and chemical analysis to characterize the capsule of the re-encapsulated strain.
• Infection studies in mice and assessment of immune responses (complement activation, cytokine production).

Main Results:

• An encapsulated strain, TYCC38-602, was created, revealing strain 602's serotype A origin.
• Restoring the capsule re-established virulence, enabling fatal infections in mice, while acapsular strain 602 remained avirulent.
• The capsule masked immune evasion mechanisms, including suppressed tumor necrosis factor alpha and nitric oxide synthase induction in macrophages.

Conclusions:

• The lack of a capsule in strain 602 explains its avirulence and altered biological activities.
• The capsule is essential for Cryptococcus neoformans virulence and immune evasion.
• The CAP64 gene product does not determine capsule serotype specificity.