Lack of vessel wall elastolysis in human invasive pulmonary aspergillosis

Abstract

In experimental studies, the apparent ability of Aspergillus fumigatus isolates to produce elastase in agar plates correlates with their ability to cause invasive pulmonary aspergillosis in mice pretreated with cortisone. Thus, elastase production may govern the pathogenicity of particular isolates. If this is so, then disruption of the elastic layers within blood vessel walls in invasive aspergillosis would be expected. To test this hypothesis, tissue blocks were prepared from nine patients with invasive pulmonary aspergillosis. Separate but immediately adjacent histological sections were stained by the Grocott and periodic acid-Schiff methods for fungal hyphae and by the elastic van Gieson technique for elastic tissue. Comparison of those segments of vessel walls infiltrated by hyphae with those not infiltrated by hyphae showed no overall loss of elastic tissue. Material from five of the cases was also stained with an unconventional combination of histochemical stains, allowing accurate identification of both fungal hyphae and elastic laminae in the same histological sections. The results showed no more disruption of elastic laminae than would be expected from simple physical displacement of elastic laminae. We conclude that if elastolysis contributes at all to invasion of vessel walls by aspergilli, then it seems to be very localized and/or transient.