Role of the lectin pathway of complement in C. albicans and P. aeruginosa infections

Role of the lectin pathway (LP) of complement in fighting two opportunistic pathogens, Candida albicans and Pseudomonas aeruginosa was assessed through a combination of in vitro assays supported by in vivo infection experiments using a unique mouse strain of total LP functional deficiency (MASP-2 -/- mouse). A highly significant difference in survival between MASP-2 -/- mice and MASP-2 +/+ littermates was observed following C. albicans infection with a lethal i.v. dose (1.4x106CFU/mouse), showing that MASP-2 -/- were significantly compromised. Challenging mice with a sub-lethal dose (4x105 CFU/mouse) revealed a significantly higher fungal load in kidneys, livers, lungs and spleens of MASP-2 -/- mice. IL-10 mRNA expression levels were only significantly upregulated in infected MASP-2 -/- mice, while mRNA expression of the protective cytokines IL-17 and INF-γ were only upregulated in MASP-2 +/+ mice. Challenging of MASP-2 -/- mice and MASP-2 +/+ controls with an intranasal dose (1x106 CFU/mouse) of P. aeruginosa revealed no significant difference in survival rates. The bacterial load with P. aeruginosa and mRNA expression profiles for TNF-α, IL-6, IL-10, MIP-2, IL-1β and INF-γ were similar in lungs of both mouse strains. The absence of the LP in MASP-2 -/- mice appears to make no difference in the susceptibility to P. aeruginosa infection as the alternative pathway seems to provide sufficient protection. The cDNA sequence of porcine MASP-2 was established to express an enzymatically inactive mutant form of porcine MASP-2 (pMASP-2A) in a mammalian cell line (CHOK1 cells). pMASP-2A was produced in large scale and used as an antigen to isolate recombinant inhibitory phage display antibodies. These antibodies will be analysed in porcine models of ischaemia/reperfusion (I/R) injury to assess the therapeutic potential of LP inhibition in limiting I/R injury and reduce morbidity and mortality in a clinically relevant experimental animal model of human disease.