Use of antibodies from single human B cells and C-type-lectin probes to map the dynamic cell surface of fungal pathogens

The cell surface of fungal pathogens encodes a suite of molecules that are recognised by pattern recognition receptors of the innate immune system resulting in the activation of immune defences. Differences in the cell wall composition of different fungi and or the same fungus organisms growing in different morphologies and in differing environments generates a moving target for immune recognition. Progress in our understanding the nature of the immune response is described using two types of novel tools. We used cloned human monoclonal antibodies from individual B cells from patients who recovered from a recent fungal infection and the lectin binding domains of a range of mannan-detecting C-type lectin receptors as probes to map dynamic changes in the cell wall. The human mAbs also showed significant potential as diagnostics and as immune compatible therapeutic reagents. We show that immune relevant epitopes revealed by Fc-lectin mapping can be diffuse or clustered, superficial or buried in the cell wall. The immune reactivity of different fungal cell surfaces was not necessarily related to the phylogenetic relationship between organisms, and mannan-detecting lectins discriminated between different types of mannans on the cell surface and between yeast, hypha and other morphologies of the same fungus. Finally the growth cycle of a fungus was shown to be accompanied by temporal masking or unmasking of particular mannan epitopes during batch culture. These experiments demonstrate that the fungal cell surface is ordered, complex and dynamically changing, making immune recognition a challenging process requiring the concerted action of multiple immune receptors operating singly and in combination.