An analysis of the organ and species immunospecificity of elastin

Characterization of elastin protein and mRNA from salmonid fish (Oncorhynchus kisutch)

1. Elastin was isolated from the bulbus arteriosus of a salmonid fish. Monoclonal and polyclonal antibodies, elicited against a CNBr digest of this protein, immunoprecipitated a polypeptide of Mr 43,000 from fish cell culture medium. 2. Cell-free translation of salmon poly A+ RNA produced a protein of approximately 43 kD that was immunoprecipitated with anti-elastin antibodies. The corresponding mRNA had an approximate Mr of 2 kb. 3. Despite similarities in amino acid composition, the differences in Mr between mammalian and salmon mRNA and protein suggest a divergence of fish and higher vertebrate elastins from an earlier ancestral gene.

Quantitation of elastin in human urine and rat pleural mesothelial cell matrix by a sensitive avidin-biotin ELISA for desmosine

A specific enzyme-linked immunosorbent assay (ELISA) was developed for the determination of desmosine, a cross-linked amino acid specific to fibrous elastin. Competition between solid phase-bound desmosine-protein conjugate and free desmosine for binding to monospecific anti-desmosine antiserum constituted the underlying principle of the assay. The conjugation of desmosine to different protein carriers was carried out with the 1-ethyl-3-(dimethylamino-propyl)carbodiimide (ECDI); rabbits were immunized with desmosine-bovine serum albumin and micro-titer plates were coated with desmosine-egg albumin. An avidin-biotin peroxidase system was used to reveal anti-desmosine antibodies bound to the desmosine-protein conjugate. As both conjugates revealed new non-specific common epitopes on the carrier proteins, prior absorption of the anti-desmosine antiserum on rabbit albumin polymerized with ECDI was required to remove the antibodies directed against these neo-antigens. The absorption procedure resulted in an increased specificity and sensitivity. Values ranging from 0.07 to 4 ng of desmosine/well could be detected and this sensitivity was greater than that obtained in previous immunoassays for desmosine. In order to assess the specificity of the test, samples containing aminoacids and urine hydrolysates were included in an assay. Some cross-reactivity was observed with the desmosine precursor lysinonorleucine and the desmosine isomer isodesmosine but, in contrast the very low cross-reactivity observed with collagen hydrolysate was similar to that exhibited by albumin hydrolysate. Analysis of urine samples from 118 normal male volunteers showed, firstly, that urinary creatinine measurement was a good indicator of the amount of urine which could be safely introduced in the assay without risk of non-specific interference by other organic compounds and, secondly, that the desmosine/creatinine ratio was a reliable index for an in vivo assessment of degraded elastin excretion. The assay also allowed quantitation of elastin fiber biosynthesis in the connective tissue matrix of cultured rat pleural mesothelial cells. This ELISA for demosine is a simple technique which should be useful for further in vivo or in vitro investigations of fibrous elastin tissue metabolism.

Distribution and organization of the elastic system fibres in healthy human gingiva. Ultrastructural and immunohistochemical study

The ultrastructural distribution and organization of the elastic system fibres, i.e. oxytalan, elaunin and elastic fibres, were studied by transmission electron microscopy and by an immunohistochemical method for the detection of elastin in healthy human gingiva. The morphological distribution of these fibres was characterized by the presence of oxytalan, elaunin and elastic fibres, respectively, in the upper, medium, and deep layers of gingival connective tissue. Anti-elastin antibody reacted with microfibrils and amorphous material of the elastic system fibres throughout the gingival connective tissue. These findings were interpreted as indicating that the microfibrils were associated with small amounts of elastin at their surface.

Newly determined carboxy terminal sequences in tropoelastin: immunologic identification in insoluble elastin

The carboxy terminal sequence of sheep, bovine and human tropoelastin (GFPGGACLGKA/SCGRKRK) has been inferred in earlier studies from sequencing of cloned complementary and genomic DNA. However, this putative carboxy terminal sequence was not found previously in peptides recovered from tryptic digests of tropoelastin. In order to determine whether the amino acid sequence described above is found in insoluble elastin, antibodies were raised against the chemically synthesized peptides with the appropriate sequences and the antibodies were shown to react with peptides derived from human, bovine, porcine, dog and hamster insoluble elastins. These results strongly suggest that the sequence (GFPGGACLGKA/SCGRKRK) at the carboxy terminus of tropoelastin is found in the elastins of many species.

Ultrastructural and biochemical modifications of rabbit arteries induced by immunization with soluble elastin peptides

Immunization of rabbits with soluble elastin peptides (kappa 1-elastin) in complete Freund's adjuvant resulted in morphological and biochemical modifications in aorta and in lung arterioles. The elastic fibers of both tissues appeared fragmented at the light microscopical and ultrastructural levels. The presence of IgG at the site of lysed elastic fibers could be evidenced by immunological techniques. In agreement with these findings, a significantly increased elastase-type protease activity could be demonstrated in aorta extracts from the immunized animals as compared to those obtained from control animals. The biosynthetic activities of aorta explants of rabbits immunized with kappa 1-elastin maintained in organ culture conditions were considerably reduced, as shown by the decrease of incorporation of [14C]lysine and [14C]glucosamine in aorta macromolecules. These results show that anti-elastin antibodies may well be involved in the pathological modifications of the arterial wall and especially in the triggering of the degradation of elastic lamellae.

Immunoreactive elastin in benign breast tissues. An immunoperoxidase study

Immunohistological localisation of elastin was achieved by means of the peroxidase-antiperoxidase method after preliminary trypsinisation of sections from 48 benign breast biopsies. The procedure allows retrospective examination of routinely formalin-fixed, paraffin-embedded breast tissue. In general the immunolocalisation of elastin showed a close microanatomical correlation with the fibres demonstrable in sections from the same blocks by standard elastic-fibre stains. Discrepancies between elastic-fibre stains and elastin immunoreactivity appear to relate to the enhanced avidity of the antibody for immature elastin. In this way sites of recent synthesis of elastin were demonstrated in the inner zone of the periductal elastica, sclerosing adenosis, and in the internal elastic lamina of breast arteries which displayed reduplication of the internal elastic lamina or intimal proliferation.

Immunological studies with human aortic elastin

Antibodies to human fetal aortic elastin were isolated from sheep immunized with alpha-elastin peptides. In preliminary tests of specificity using passive hemagglutination, partial cross-reactivity was demonstrated with alpha-elastin from other species. However, in a double antibody radio-immunoassay alpha-elastin peptides from other mammalian species failed to compete with 125I-labelled human alpha elastin. These results suggest the existence of at least two different antigenic sites on the elastin molecule. One, a high affinity site, demonstrates species specificity at low antigen/antibody concentrations. The other, a low affinity site, is common to mammalian elastins and is demonstrated at high antibody/antigen concentrations. In the radioimmunoassay the antibodies showed considerably less avidity for adult human alpha-elastin than for the fetal antigen. This implies that the species specific site is age-dependent and probably involves the cross-linking region of the elastin molecule. Using the sheep antiserum immunohistochemical staining of elastic tissue has been developed. This should prove to be a useful technique for studying polymeric elastin in intact tissue by light microscopy and at the ultrastructural level.