The Aspergillus fumigatus cspA Gene Encoding a Repeat-Rich Cell Wall Protein Is Important for Normal Conidial Cell Wall Architecture and Interaction with Host Cells

cspA (for cell surface protein A) encodes a repeat-rich glycophosphatidylinositol (GPI)-anchored cell wall protein (CWP) in the pathogenic fungusAspergillus fumigatus . The number of repeats incspA varies among isolates, and this trait is used for typing closely related strains ofA. fumigatus . We have previously shown that deletion ofcspA is associated with rapid conidial germination and reduced adhesion of dormant conidia. Here we show thatcspA can be extracted with hydrofluoric acid (HF) from the cell wall, suggesting that it is a GPI-anchored CWP. ThecspA -encoded CWP is unmasked during conidial germination and is surface expressed during hyphal growth. Deletion ofcspA results in weakening of the conidial cell wall, whereas its overexpression increases conidial resistance to cell wall-degrading enzymes and inhibits conidial germination. Double mutant analysis indicates thatcspA functionally interacts with the cell wall protein-encoding genesECM33 andGEL2 . Deletion ofcspA together withECM33 orGEL2 results in strongly reduced conidial adhesion, increased disorganization of the conidial cell wall, and exposure of the underlying layers of chitin and β-glucan. This is correlated with increasing susceptibility of the ΔcspA , ΔECM33 , and ΔcspA ΔECM33 mutants to conidial phagocytosis and killing by human macrophages and hyphal damage induced by neutrophils. However, these strains did not exhibit altered virulence in mice with infected lungs. Collectively, these results suggest a role forcspA in maintaining the strength and integrity of the cell wall.