The mechanisms by which hookworm larvae infect almost one-fourth of the world's population and then develop in their human host are poorly understood. The proposed research will contribute to an understanding of these processes at the molecular level. After host entry, larvae of the genus Ancylostoma can exercise one of two developmental options that allows them to either (1) continue tissue invasion and development or (2) interrupt their development and undergo a facultative growth arrest in the host tissues (hypobiosis). Arrested hypobiotic larvae are resistant to conventional anthelminthics and thus thwart traditional attempts at mass population chemotherapy when they enter the intestinal tract months after the initial infection. Moreover, larvae that arrest in a lactating mother can mobilize into breast milk to cause neonatal infection. New solutions to chemoprophylaxis or immunoprophylaxis are urgently needed; their design is dependent on elucidating the biochemical mechanisms that allow larvae to either invade tissue or arrest. To elucidate the basis for host invasion and development we will isolate the major hydrolases, an 49 kDa hyaluronidase that serves to degrade hyaluronic acid bridges connecting epidermal keratinocytes, and to facilitate dermal migration and a 68 kDa metalloprotease that also facilitates migration and appears to undergo post-translational processing during development. We will develop both antibody probes to these enzymes as well as nucleic acid probes wither by PCR or on the basis of N-terminal amino acid data. These probes will serve as reagents to identify cDNA clones from an expression library and to further explore our hypothesis that larval activation and development correlate biochemically with post-translational processing and phosphorylation. To elucidate the basis for arrest we will characterize protein kinase activities from infective larvae that serve as central components of signal transduction pathways and mediate developmental decisions. One of these a cAMP-dependent protein kinase, appears to mediate phosphorylation of a 68 kDa protein. A heterologous antibody to C. elegans cAMP-dependent protein kinase recognizes the hookworm protein on immunoblots and will be used as a reagent for screening a cDNA library. The pharmacologic manipulation of parasite-derived protein kinases may offer a new approach to chemotherapy by taking larvae out of arrest.