Application of novel serine protease activity-based probes for cathepsin G detection in primary human antigen presenting cells after EBV and HIV infection

Cathepsins are crucial in antigen processing in the major histocompatibility complex class II (MHC II) pathway. Within the proteolytic machinery three classes of proteases, cystein-, aspartic-, and serine proteases, are present in the endocytic compartments. The combined action of these proteases generates antigenic peptides from antigens, which are loaded to MHC II molecules for CD4+ T cell presentation. We generated a novel high sensitive phosphonate-based serine protease activity-based probe to visualize cathepsin G (CatG) activity in low amounts of cell lysate. Application of this activity-based probe for CatG detection showed no differences in CatG activity in primary human antigen presenting cells (APC), when exposed with Epstein-Barr virus (EBV). However, CatG activity was increased in monocytes and macrophages after exposure with the human immunodeficiency virus (HIV), indicating a defense mechanism of these APC after viral infection. Here we demonstrate that our serine protease activity-based probe can be used to detect CatG activity in low numbers of primary cells from human peripheral blood.