Monoclonal antibody mediated capsular reactions (Quellung) in Cryptococcus neoformans

Capsular reactions ('Quellung') visible by light microscopy were observed when capsule-binding monoclonal antibody (mAb) was added to Cryptococcus neoformans yeast cells. Capsular reactions were observed with capsule-binding IgM, IgG1, IgG2a, IgG2b, IgG3 and IgA mAbs. Scanning electron microscopy revealed that mAb binding produced a structural change in the fibrillar network of the capsule. The occurrence of capsular reactions with mAbs indicate that this phenomenon can be produced by the binding of antibody to a single epitope.