Binding of Cryptococcus neoformans to heterologously expressed human complement receptors

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Monoclonal antibodies (MAb) previously suggested complement receptors (CR) are crucial for binding serum-opsonized Cryptococcus neoformans to macrophages.
• Previous findings implied either synergistic CR interactions or non-specific MAb effects in C. neoformans binding.

Purpose of the Study:

• To investigate the independent roles of complement receptors 1, 3, and 4 in binding C. neoformans.
• To utilize transfected Chinese hamster ovary (CHO) cells to dissect individual receptor contributions.

Main Methods:

• Chinese hamster ovary (CHO) cells were stably transfected with human complement receptors 1 (CR1), CR3, or CR4.
• Transfected CHO cells were challenged with serum-opsonized C. neoformans to assess binding avidity and internalization.
• Selective opsonization with C3b and iC3b fragments was used to determine preferential binding to specific receptors.

Main Results:

• CHO cells expressing CR1, CR3, or CR4 independently bound C. neoformans.
• Binding avidity was highest for CR3, followed by CR1, then CR4.
• A significant percentage of C. neoformans (18.5–27.3%) were internalized by cells expressing each receptor.
• CR1 preferentially bound C3b-opsonized targets, while CR3 preferentially bound iC3b-opsonized targets.

Conclusions:

• CR1, CR3, and CR4 are independently capable of binding C. neoformans opsonized with complement C3 fragments.
• Transfected cell lines are effective tools for identifying individual receptor roles in microbial pathogen binding.
• This study clarifies the distinct roles of CR1, CR3, and CR4 in C. neoformans recognition.