Nanobodies (also called single website antibodies, sdABs) are isolated recombinant VHHs that retain the full antigen-binding capacity of the original HCAb. monoclonal antibodies can be used as probes for MET detection or as bullets to target MET-expressing tumor cells, therefore pointing to their use in analysis and therapy. angiogenesis [47,80]. Two additional mAbs (DN-30 and DL-21) that behave as Closantel partial agonists and bind to different epitopes of the receptor were able to activate only motility and safety from apoptosis [47,81,82]. All the antibodies were able to result in receptor phosphorylation, which was found to be purely dependent on mAb bivalence; in fact, the monovalent Fab was ineffective, and activation was recovered by the addition of a secondary anti-mouse Ig antibody . Only the full agonist mAbs were found to be able to induce and sustain the manifestation of urokinase-type plasminogen activator (uPA) receptor for long Closantel term periods of time . By binding uPA in the cell surface, this Closantel receptor focalizes there a proteolytic machinery, which can recruit and activate metalloproteases with potent extracellular matrix-degrading action. This activity takes on a key part in invasive growth, a distinguished feature of the HGF/MET axis, which combines proliferation and migration and is particularly important in tubulogenesis. Using the two classes of agonist mAbs, the dissection of the two groups of biological responses, previously analyzed in canine epithelial cells, was confirmed also for Kaposi sarcoma cells . In this case, the partial agonism of the mAbs correlated with a reduced and short ERK-1/2 activation, compared with that achieved by full agonist mAbs, while in the case of additional transducers or adaptorsPI 3kinase, JNK and Gab-1no variations were recognized. Therefore the PI 3 kinaseCAkt pathway is also fully triggered by partial agonist mAbs, which can elicit motogenicity and safety by apoptosis. The epitopes identified by the mAbs DO-24 and DN-30 have been localized outside the HGF binding site, since they do not compete with the natural ligand. In particular, the DN-30 mAb binds in the IPT-4 region, while the DO-24 mAb binds round the PSI-IPT-1. While both mAbs induce receptor activation, because of their bivalence, only DO-24 is definitely a full agonist advertising all MET-mediated biological responses. It follows that simple MET dimerization is not enough for full receptor activation, for which further requirements need to be met, which may be linked to the particular epitope identified by the antibody. It is worth noting the epitope identified by DO-24 overlaps with the primary binding site of the Internal B protein, which activates the MET receptor and promotes the bacterial invasion of the sponsor cells, as recognized Epha5 by cross-inhibition experiments  and co-crystallization of the MET ectodomain with Internalin B . The DN-30 mAb is definitely a partial MET agonist, but also behaves as an antagonist, and has been further developed like a monovalent antibody for anti-cancer therapy (observe Antagonist MET mAbs section). The different contrasting activities of the bivalent form may be linked to the amount of mAbs used in the different experimental settings; indeed, the agonistic activity is generally more pronounced at low doses, and disappears at higher doses . The fact the same mAbs can behave as partial agonist and antagonist was observed also for Trastuzumab . The agonist mAbs were able to guard cardiomyoblasts from apoptosis induced by oxidative stress or by hypoxia induced by cobalt chloride treatment [81,82]. They also counteracted apoptosis, as analyzed by different guidelines such as DNA fragmentation, cell shrinkage, annexin V positivity, mitochondrial translocation of bax, caspase activation, and nuclear element. Safety from apoptosis was dependent on an active MET, since it could be inhibited by treatment of cardiomyoblasts with MET-specific si-RNA or from the MET tyrosine kinase inhibitor PHA-665752. MET agonist antibodies proved to be effective in inhibiting autophagy as well, a less regarded as mechanism of cell damage in heart diseases. Indeed, it is acknowledged that basal levels of autophagy are required for cardiac homoeostasis, since cardiomyocytes are long-living cells and autophagy allows the removal of damaged molecules and organelles . However, autophagy can act as a double-edged sword in the cardiovascular system and indeed an autophagic flux, with the involvement of the Beclin p62, LC3, was induced in response to ischemia/reperfusion injury, which therefore resulted in detriment to the cells [82,88,89]. The safety from autophagy afforded from the agonist mAbs, as well as from the natural ligand, was mTOR dependent, since it was prevented by the specific mTOR inhibitor Temsirolimus . MET agonist mAbs were also able to result in Closantel motility of cardiomyocytes, as.