Anti-cathepsin D chicken IgY antibodies: Characterisation, cross-species reactivity and application in immunogold labelling of human splenic neutrophils and fibroblasts

Hyperexpression, alteration of trafficking and secretion of cathepsin D has been linked with tumour invasion and inflammation, To study these phenomena in a variety of cells large quantities of anti-cathepsin D antibodies and the appropriate immunogen are required. As the human immunogen for studies on human tissue is less easily accessed, antibodies to both human and porcine cathepsin D were raised in chickens, as high levels of antibody may be recovered from egg yolks, and the potential cross-reactivity of the anti-porcine cathepsin D IgY antibody was assessed, This preparation cross-reacted strongly with human cathepsin D, comparing favourably with the reactivity of the chicken antibody to the human immunogen. The necessity for isolating human immunogen can thus be circumvented, The cross-species-reacting chicken IgY was successfully used to localise cathepsin D in immunogold labelling of human tissues. To our knowledge, IgY antibodies have not previously been used by other researchers for this purpose, Application of the cross-reacting antibody to human splenic neutrophils (PMNs) has confirmed the presence of cathepsin D in some granules. Double labelling has shown these to be novel subpopulations of azurophil granules. Cathepsin D may, therefore, be relevant in the invasive and inflammatory activities of PMNs and a target for therapeutic strategies.