Calcium-dependent protection from complement lysis in Naegleria fowleri amebae

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Pathogenic Naegleria fowleri amebae exhibit resistance to serum complement lysis.
• Mechanisms of resistance, such as surface glycoproteins and membrane attack complex (MAC) removal, are known, but specific mediators are undefined.

Purpose of the Study:

• To investigate the role of calcium ions (Ca2+) in initiating complement resistance in N. fowleri.
• To compare the effect of Ca2+ on complement resistance between pathogenic N. fowleri and non-pathogenic N. gruberi.

Main Methods:

• Chelation of extracellular and intracellular calcium using EGTA and BAPTA-AM, respectively.
• Treatment with ionomycin to assess the effect of increased intracellular calcium.
• Utilizing fura-2 labeling to monitor Ca2+ influx upon complement component C9 deposition and MAC formation.

Main Results:

• Chelation of Ca2+ significantly increased complement-mediated lysis of N. fowleri.
• Ca2+ chelation did not alter the complement sensitivity of N. gruberi.
• Ionomycin treatment enhanced N. fowleri survival against complement lysis, suggesting a threshold Ca2+ level is required for resistance.
• Differential Ca2+ influx was observed in N. fowleri compared to N. gruberi after MAC formation.

Conclusions:

• Calcium ions (Ca2+) play a significant role in mediating complement resistance in pathogenic Naegleria fowleri.
• Ca2+ does not appear to influence the complement sensitivity of non-pathogenic Naegleria gruberi.
• These findings highlight Ca2+ as a potential target for understanding and combating N. fowleri infections.