The "D. melanogaster" immune system can be divided into two responses: humoral and cell-mediated. The former is a systemic response mediated in large part through the "Toll" and "Imd" pathways, which are parallel systems for detecting microbes. Other pathways including the stress response pathways JAK-STAT and P38, nutritional signalling via FOXO, and JNK cell death signalling are all involved in key physiological responses to infection. "D. melanogaster" has a fat body, which is analogous to the human liver. The fat body is the primary secretory organ and produces key immune molecules upon infection, such as serine proteases and antimicrobial peptides (AMPs). AMPs are secreted into the hemolymph and bind infectious bacteria and fungi, killing them by forming pores in their cell walls or inhibiting intracellular processes. The cellular immune response instead refers to the direct activity of blood cells (hemocytes) in "Drosophila", which are analogous to mammalian monocytes/macrophages. Hemocytes also possess a significant role in mediating humoral immune responses such as the melanization reaction.