Isolation from human plasma of a protein fraction with thymic hormone-like activity

Immuno-enhancing activity of the amino-terminal domain of human prealbumin: isolation, characterization and synthesis

A decapeptide isolated from highly purified preparations of human prealbumin was able to restore azathioprine (Az) sensitivity, a property of a sub-class of T-lymphocytes, to the spleen rosette-forming cells (RFC) of adult thymectomized (ATx) mice in vitro. The peptide was sequenced by the Edman method and shown to correspond to the ten amino-terminal residues of prealbumin, Gly-Pro-Thr-Gly-Thr-Gly-Glu-Ser-Lys-Cys. Synthesis of this peptide by solid phase methodology confirmed its activity both in vitro and in vivo. Synthesis of a number of structural analogues indicated that the amino-terminal deca, undeca and dodecapeptides of prealbumin as well as some of their derivatives were also able to restore Az sensitivity to RFC in vitro and in vivo. The Cys10 residue and the Glu7 residues both contributed significantly to potency in vitro. Removal of up to three amino acids from the N-terminus of the decapeptide led to a progressive loss of activity. The data indicates that the ability of human prealbumin to restore the Az sensitivity to the RFC of adult Tx mice is intrinsic to the protein and resides in the amino-terminal domain of the molecule.

The effects of homogeneous human prealbumin on in vitro and in vivo immune responses in the mouse

A highly purified preparation of human prealbumin was shown to potentiate the sensitivity of rosette spleen forming cells of adult thymectomized mice to azathioprine in vitro and in vivo and to induce the appearance of the Thy 1, 2 antigen in vitro on spleen cells of adult thymectomized mice. Prealbumin also enhanced IgM antibody synthesis to sheep red blood cells (SRBC) in vitro in 12 week old mice and in vivo in aged (45 - 58 week old) and nude (nu/nu) mice. In vivo administration, to mice that had been pre-treated with hydrocortisone, resulted in a decrease in the specific activity of thymocyte terminal deoxynucleotidyl transferase. The data indicate that the prealbumin molecule possesses immunopotentiating properties in a number of in vitro and in vivo immunocompromised murine models and that the immuno-enhancing properties of the partially purified preparation previously described were in fact due to the prealbumin component and not to other contaminating proteins.

Induction of T-cell maturation by a cloned line of thymic epithelium (TEPI)

A cloned cell line of thymic origin has been characterized as epithelial in nature. A description of the procedures for derivation and cloning of the cell line includes use of epidermal growth factor. The thymic epithelial (TEPI) cell line is Ia antigen positive, forms desmosomes, and produces an extracellular fibronectin matrix. The supernatant from confluent monolayers of TEPI was tested for its ability to promote thymocyte functional activity. TEPI supernatant (TEPI SN) was demonstrated to greatly enhance the response of peanut agglutinin-positive thymocytes to alloantigen, as measured by cell-mediated lympholysis. Furthermore, preincubation of peanut agglutinin-positive thymocytes with TEPI SN prior to allostimulation resulted in marked enhancement, thus distinguishing it from interleukin 2. Finally, TEPI SN was demonstrated to induce interleukin 2 production by peanut agglutinin-positive thymocytes in the presence of concanavalin A. This activity was demonstrated not to be due to interleukin 1, which is absent in TEPI SN. Preliminary biochemical analysis indicates that the biological activity is associated with a Mr 50,000 entity. The data suggest that TEPI produces a soluble factor capable of inducing function of an immature thymocyte subpopulation into an IL 2 producer.

Human prealbumin fraction: effects on cell-mediated immunity and tumor rejection

The effect of human prealbumin fraction as allogeneic cell-mediated immunity in primary sensitization cultures of murine spleen cells was studied by 3H-thymidine uptake and specific 51Cr release assays. Prealbumin caused a dose-dependent augmentation of these responses. Human serum albumin, bovine serum albumin, and calf-thymosin fraction 5 had little effect. Prealbumin was active when added on day 0 or 1 but not thereafter. Prealbumin added to effector cells from immunized mice did not change their lytic activity. Prealbumin, but not human serum albumin or thymosin fraction 5, augmented secondary cell-mediated immunity in culture after primary immunization in mice. A slow growing mammary tumor line, which originated as a spontaneous mammary tumor in a DBA/2 HaDD breeder mouse, initially grows in 100% of DBA/2J mice but is then rejected in 10-20% of them. When prealbumin (59 microgram/day) was given subcutaneously for 2 weeks to DBA/2J mice and the tumor implanted 2 weeks later. 78% of the mice rejected the tumor and were then resistant to a rechallenge.