Further evidence for the procidin function of C3

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Human polymorphonuclear leucocytes (PMNs) are crucial immune cells involved in combating fungal infections like Candida.
• The role of serum factors and complement system components in PMN-mediated fungal killing is complex and requires further elucidation.

Purpose of the Study:

• To investigate the specific roles of serum components and complement C3 in human PMN phagocytosis and killing of Candida.
• To determine the mechanisms by which C3 influences PMN candidacidal activity.

Main Methods:

• Utilized heat-inactivated serum to assess its effect on PMN phagocytosis, oxygen consumption, and Candida killing.
• Investigated the requirement of C3 for PMN-mediated superoxide anion generation and iodination.
• Studied the impact of purified C3 addition to C3-deficient serum on phagocytic killing.
• Examined the effects of trypan blue and heparin on PMN ingestion and Candida killing.

Main Results:

• Heat-inactivated serum supported Candida ingestion by PMNs but did not enhance oxygen consumption or killing.
• Complement component C3 was found to be essential for activating PMN candidacidal mechanisms, including superoxide anion generation and iodination.
• Restoration of phagocytic killing was observed upon adding purified C3 to C3-deficient serum.
• Trypan blue, an antagonist of C3 receptors, and heparin, which affects C3 conversion, both inhibited efficient Candida killing by PMNs.

Conclusions:

• Phagocytic killing of Candida by human PMNs is not solely dependent on yeast ingestion.
• Effective killing requires the interaction of humoral factors (termed procidins) with specific receptors on PMNs that initiate microbicidal mechanisms.
• Complement C3 activation products play a critical role in stimulating PMN phagocytic killing by engaging their corresponding receptors.