Design and application of a polyclonal peptide antiserum for the universal detection of leptin protein.

An epitope-specific polyclonal antiserum was produced in rabbits immunized against a synthetic 15 amino acid peptide (QRVTGLDFIPGLHPV) derived from the coding sequence reported for the porcine leptin gene (GenBank Accession No. U59894). This peptide contains a core sequence comprised of eight amino acids (GLDFIPGL) that is totally conserved in all leptin proteins studied to date. Purified recombinant human, mouse, rat, pig, and chicken leptin proteins were separated by polyacrylamide gel electrophoresis (SDS-PAGE) and electro-blotted onto PVDF membranes. Western blots were developed employing the leptin-specific peptide antiserum with an alkaline-phosphatase-conjugated anti-rabbit IgG second antibody chromogenic system. The peptide antiserum was found to be highly specific for leptin which exhibited an estimated molecular weight of about 16 kDa for all species analyzed. The sensitivity of the Western blot assay was not sufficient to permit the direct detection of leptin in chicken serum or plasma. However, with this assay we were able to detect native leptin protein in an enriched fraction prepared from chicken plasma using a combination of gel filtration and ion exchange column chromatography. Slot blots indicated a potential application of the immunostaining technique for quantitative analysis of leptin protein. Finally, the peptide antiserum was successfully employed to localize leptin protein by immunohistochemical staining of thin sections prepared from adipose (chicken and pig) and liver (chicken) tissue samples. This study is the first to report a polyclonal peptide antiserum that apparently recognizes intact leptin protein, both native and recombinant, regardless of the species of origin.