Preferential binding of lysozyme to elastic fibres in pulmonary emphysema

Lysozyme is increased in inflammatory reactions and is a component of the extracellular matrix, but its possible role in lung diseases such as emphysema and interstitial fibrosis has not been investigated.

To characterise differences in lysozyme content among normal, emphysematous, and fibrotic human lungs, tissue sections obtained from necropsy specimens were immunostained with rabbit polyclonal anti-human lysozyme antibody using the labelled streptavidin-biotin peroxidase method. The immunostained sections were evaluated semi-quantitatively (grading the degree of immunostaining on a scale of 0-4). To determine if degradation of the extracellular matrix affects lysozyme binding, hyaluronidase-treated normal lung tissues were incubated with egg white lysozyme, immunostained with the lysozyme antibody, which crossreacts with egg white lysozyme, and evaluated for degree of staining.

Lysozyme immunostaining was significantly increased in lungs with pulmonary emphysema compared with normal or fibrotic tissues (3.4 versus 1.6 and 1.9, respectively; p < 0.05) and was preferentially associated with interstitial elastic fibres. Hyaluronidase-treated lung tissues incubated with lysozyme showed increased immunostaining for this protein compared with untreated controls (1.9 versus 1.2; p < 0.05).

The results suggest that damage to elastic fibres and/or the surrounding extracellular matrix increases lysozyme binding. It is hypothesised that attachment of lysozyme to elastic fibres may interfere with their repair and possibly enhance the progression of pulmonary emphysema.