Fungal complement factor H receptor and virulence

In the century of transplantation and chemotherapeutic immunosuppression, Candida represents the major cause of opportunistic fungal infection in immunocompromised hosts. For immune defence against Candida the innate immunity (in particular polymorphonuclear leukocytes and complement), plays a more important role than the acquired immune response, which explains the more severe clinical picture when defects in the phagocytic system occur. Complement facilitates chemotaxis of phagocytes and opsonisation of the invader and is tightly controlled by several regulators, among these factor H and FHL-1 (the latter representing an alternatively spliced aminoterminal truncated version of Factor H). Although an impaired immune status of the host is likely the most important factor leading to disease, virulence factors of the fungus also play a role. These comprise molecules by which Candida can adhere to and invade the host and cell surface structures enabling the yeast to escape or undermine host defence and in particular the complement system. This dual way to subvert host defence can in particular be accomplished by surface molecules which function both as adhesion molecules and complement regulators, such as bound factor H and FHL-1. It is thus no surprise that several pathogenic micro-organisms evade their destruction by binding factor H and FHL-1. We recently discovered the binding of factor H and FHL-1 on the surface of C. albicans. Two different receptors are likely involved on C. albicans; the closely related yeast, C. dubliniensis is also able to bind factor H. We want to identify the factor H-receptors on C. albicans and C. dubliniensis, and their corresponding genes, by probing C. albicans expression libraries with purified factor H, followed by PCR methods to identify the corresponding receptor gene in C. dubliniensis and simultaneously by biochemical isolation using immune affinity chromatography with factor H adsorbed to sepharose beads. The relevance of these receptors for immune evasion by Candida will be assessed by knocking the respective genes out and by testing the deletion mutants for factor H / FHL-1 binding and for resistance to complement-mediated phagocytosis and for other fungal virulence properties, e.g. the ability to secrete aspartic proteases and adhesion to host cells, using the arsenal of assays established in the applicant`s laboratory. Finally, the deletion mutants will be evaluated in mice. Characterising these receptors may represent the first step in designing blocking agents to overcome fungal evasion - a milestone in antimycotic therapy.

In the century of transplantation and chemotherapeutic immunosuppression, Candida represents the major cause of opportunistic fungal infection in immunocompromised hosts. For immune defence against Candida the innate immunity (in particular polymorphonuclear leukocytes and complement), plays a more important role than the acquired immune response, which explains the more severe clinical picture when defects in the phagocytic system occur. Complement facilitates chemotaxis of phagocytes and opsonisation of the invader and is tightly controlled by several regulators, among these factor H and FHL-1 (the latter representing an alternatively spliced aminoterminal truncated version of Factor H). Although an impaired immune status of the host is likely the most important factor leading to disease, virulence factors of the fungus also play a role. These comprise molecules by which Candida can adhere to and invade the host and cell surface structures enabling the yeast to escape or undermine host defence and in particular the complement system. This dual way to subvert host defence can in particular be accomplished by surface molecules which function both as adhesion molecules and complement regulators, such as bound factor H and FHL-1. It is thus no surprise that several pathogenic micro-organisms evade their destruction by binding factor H and FHL-1. We recently discovered the binding of factor H and FHL-1 on the surface of C. albicans. Two different receptors are likely involved on C. albicans; the closely related yeast, C. dubliniensis is also able to bind factor H. We want to identify the factor H-receptors on C. albicans and C. dubliniensis, and their corresponding genes, by probing C. albicans expression libraries with purified factor H, followed by PCR methods to identify the corresponding receptor gene in C. dubliniensis and simultaneously by biochemical isolation using immune affinity chromatography with factor H adsorbed to sepharose beads. The relevance of these receptors for immune evasion by Candida will be assessed by knocking the respective genes out and by testing the deletion mutants for factor H / FHL-1 binding and for resistance to complement-mediated phagocytosis and for other fungal virulence properties, e.g. the ability to secrete aspartic proteases and adhesion to host cells, using the arsenal of assays established in the applicant`s laboratory. Finally, the deletion mutants will be evaluated in mice. Characterising these receptors may represent the first step in designing blocking agents to overcome fungal evasion - a milestone in antimycotic therapy.