ONTOGENY, IMMUNOCYTOCHEMICAL LOCALIZATION, AND BIOCHEMICAL-PROPERTIESOF THE PREGNANCY-ASSOCIATED UTERINE ELASTASE CATHEPSIN-G PROTEASE INHIBITOR, ANTILEUKOPROTEINASE (ALP) - MONOSPECIFIC ANTIBODIES TO A SYNTHETIC PEPTIDE RECOGNIZE NATIVE ALP

Expression of the mRNA encoding the elastase/cathepsin-G protease inhi bitor, antileukoproteinase (ALP), is highest in pig uterus during mid- and late pregnancy, suggesting a stage of pregnancy-dependent role fo r ALP in feto-maternal interactions. To elucidate a function for ALP i n these events, immunogenic probes were developed to localize sites of ALP expression in the environment of the developing fetus. Monospecif ic antibodies raised against a 16-mer synthetic peptide corresponding to residues 21-36 (ALP 16P) of the deduced amino acid sequence of pig uterine ALP were generated by active immunization of sheep. ALP 16P co njugated to keyhole limpet hemocyanin elicited high titer antibodies t hat were specific to ALP. The antipeptide antibodies were used to char acterize pig uterine ALP from allantoic fluids. Uterine ALP has an app roximate mol wt of 14,000 and a pI of 8.2 and exhibits elastase inhibi tor activity. Amino-terminal amino acid sequencing of uterine ALP indi cated the sequence AENALKGGACPPRKIVQC, which has 44% identity with the corresponding region in human bronchial ALP. RIA for ALP, developed u sing ALP 16P as standard and iodinated tracer, demonstrated the presen ce of immunoreactive ALP in early, mid-, and late pregnant endometrium and myometrium, placenta, allantoic fluids, fetal cord blood, and fet al liver. ALP was undetectable in the maternal circulation. The ALP le vels in endometrium, allantoic fluids, and fetal cord blood changed wi th the stage of pregnancy; however, ALP content in placenta, myometriu m, and fetal liver, although different among tissues, remained invaria nt during gestation. By immunocytochemical analyses, ALP was localized in the glandular epithelium of the uterus, in placenta, and in fetal liver, consistent with the presence of immunoreactive ALP as measured by RIA. The localization of uterine ALP in placenta and its correspond ing transport to fetal circulation provide strong evidence to support a physiological function for the protease inhibitor in the biological mechanisms controlling fetal development in utero.