A major characteristic of all fungi is the presence of a cell wall that surrounds the cell of these eukaryotic microorganisms and protects the fungus against external stresses. The central skeleton of the fungal cell wall of the human opportunistic pathogen Aspergillus fumigatus is composed of chitin and branched b1,3 glucans. In addition to this fibrillar skeleton, polysaccharides that are a 1,3 glucan, galactomannan and galactosaminogalactan play the role of cement for the wall structure. These polymers are also the major component of the extracellular matrix which glues together the hyphae of a colony in vitro and in vivo. Because of their extracellular location, these polysaccharides play also an essential role during the interactions with the fungal host. During my talk, I will discuss the immune response of the host towards the constitutive cell wall polysaccharides and show that they play an active role during infection.