The authors postulated this to be due to increased proteolysis resulting from the elevation of plasmin or other proteases derived from somatic cells, leading to the breakdown of casein and the influx of blood proteins that are relatively resistant to proteolysis (e.g., immunoglobulins, IgG, and bovine serum albumin) into milk via the paracellular pathways that proliferate during mastitis [36]. Here, PLG is linked to mastitis.