Activation of the alternative complement pathway by Trichomonas vaginalis

Area of Science:

• Immunology
• Parasitology
• Microbiology

Background:

• Trichomonas vaginalis is a parasite causing significant human infections.
• The host immune response, particularly serum-mediated lysis, plays a role in controlling T. vaginalis.
• The precise mechanisms of serum-mediated T. vaginalis lysis are not fully understood.

Purpose of the Study:

• To investigate the complement system's role in the lysis of Trichomonas vaginalis by normal human and guinea pig serum.
• To elucidate the specific complement pathways involved in parasite killing.

Main Methods:

• Serum lysis assays using normal and complement-deficient human and guinea pig sera.
• Heat inactivation and chelation (ethylenediaminetetraacetate, ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetic acid/Mg2+) to assess complement pathway involvement.
• Indirect immunofluorescence to detect complement component 3 (C3) deposition on the parasite surface.
• Properdin-depleted serum to specifically assess the alternative complement pathway.

Main Results:

• Normal human and guinea pig sera effectively lysed T. vaginalis.
• Serum deficient in C3 or C8 failed to lyse the parasite, indicating complement involvement.
• Heating serum or using ethylenediaminetetraacetate abolished lytic activity.
• Indirect immunofluorescence confirmed C3 fixation on the T. vaginalis surface.
• Properdin-depleted serum showed reduced lysis, implicating the alternative pathway.
• Guinea pig serum lacking C4 and classical pathway inhibition did not affect lysis, further supporting the alternative pathway's dominance.

Conclusions:

• The lysis of Trichomonas vaginalis by normal serum is mediated by the complement system.
• The alternative complement pathway is the primary mechanism responsible for serum-induced T. vaginalis killing.
• Complement component 3 (C3) deposition on the parasite surface is a key event in this lytic process.