Alpha-fetoprotein (AFP) is a tumor-associated embryonic serum glycoprotein, existing in the circulation as a heterogeneous population of closely related molecular variants. The biological function(s) of AFP is not known, but the precisely regulated expression of AFP molecules during ontogenetic development and in certain diseases is consistent with an immunoregulatory function. / The present thesis examines the functional significance of murine AFP microheterogeneity. In the initial phase of this study, seven individual AFP isoforms were purified with a novel separation protocol developed on Mono Q anion-exchange columns linked to an FPLC system. All seven subspecies were further characterized by isoelectric focusing gels, immunoblot analysis, molecular weight determination, and sialic acid composition studies. When all seven variants were tested in several AFP sensitive immune assays, we determined that all the immunosuppressive activity of native AFP was localized to a single distinct molecular variant. This isoform, AFP-1, exhibited an isoelectric point of pH = 5.1, contained 1 mol of sialic acid/mol of protein, and represented approximately 6% of the total population of naturally occurring AFP isoforms isolated from the amniotic fluid at days 15-19 of murine gestation. Further studies indicated that sialic acid expression on the carbohydrate portion of the AFP molecules was unlikely to be involved in the suppressor function. / Since it has been reported that the polyunsaturated fatty acids arachidonic acid and docosahexaenoic acid complexed to AFP molecules may be necessary for the expression of AFP-mediated immunoregulatory activity, we also examined the potential contribution of these polyunsaturated fatty acids to the immunoregulative function of the active isoform. Gas liquid chromatographic analyses, delipidation procedures and fatty acid reassociation experiments indicated that these fatty acids are unlikely to contribute to AFP-mediated immunosuppressive activity. We also determined that MAF-derived AFP from different gestational time points including days 10.5, 12.5, 14.5, 16.5, and 18.5 exhibits immunosuppressive activity in vitro. All the above results are the first direct demonstration that individual molecular variants of murine AFP have distinct immunoregulatory properties. This should facilitate a better comprehension of the relationship of molecular structure to biological function of AFP molecules during fetal development.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.74568 |
| Date | January 1990 |
| Creators | Van Oers, Nicolai S. C. (Nicolai Stanislas Cyrille) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Microbiology and Immunology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001167912, proquestno: AAINN66489, Theses scanned by UMI/ProQuest. |
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