How the immune system reacts to foreign, non-self and endogenous so-calles danger signals is incompletely understood. Danger signals emerge i.e. as a consequence of aberrant overgrowth of tissue, which in turn is often associated with cellular stress and cell death. Tissue that exposes danger signals to the immune system is often referred to as altered self to discriminate it from self, which by definition does not elicit an immune response. The aim of my disseration was to investigate how altered self can activate the immune systen in insects.