It has been proposed that a second SPE-like enzyme similarly acts to activate Spatzle, as loss of SPE does not completely reduce the activity of Toll signalling, however no second SPE has yet been identified. A number of serine proteases are yet to be characterized, including many with homology to SPE. The Toll pathway also interacts with renal filtration of microbiota-derived peptidoglycan, maintaining immune homeostasis. Mechanistically, nephrocytes endocytose Lys-type PGN from systemic circulation and route it to lysosomes for degradation. Without this, Toll signalling is constitutively activated, resulting in a severe drain on nutrient reserves and a significant stress on host physiology.