The biosynthesis of HLA-A, -B, and -C antigens was examined in the two lymphoblastoid cell lines DAUDI and RAJI. In RAJI cells the HLA-A, -B, and -C antigen heavy chains become core-glycosylated in the endoplasmic reticulum as evidenced by their sensitivity to endo-H digestion and tunicamycin treatment. Beta2-Microglobulin is present in excess in the endoplasmic reticulum of the RAJI cells and associates with the heavy chain at the time of synthesis of the heavy chain. Pulse-chase experiments demonstrated that the RAJI HLA-A, -B, and -C antigen heavy chains become terminally glycosylated since their changed characteristics included resistance to endo-H digestion, sensitivity to neuraminidase treatment, and incorporation fucose. DAUDI HLA-A, -B, and -C antigen heavy chains are synthesized normally and become core-glycosylated but not terminally glycosylated. Other glycosylated cell surface proteins, like the HLA-DR antigens, display normal glycosylation in DAUDI cells. Therefore it is unlikely that the absence of terminally glycosylated HLA-A, -B, and -C antigen heavy chains is the result of a general defect in the biosynthetic machinery of DAUDI cells. However, DAUDI cells lack the ability to synthesize beta2-microglobulin, the common subunit of all HLA-A, -B, and -C antigens. Therefore, it seems reasonable to conclude that beta2-microglobulin is of importance for intracellular transport of newly synthesized HLA-A, -B, and -C antigens.

Anti-idiotypic antibodies have been raised against antibodies to retinol-binding protein (RBP) and to insulin. After absorption the anti-idiotypic antibodies recognized the antigen-combining sites of the antibodies used as the immunogen but of no other antibodies. Some of the anti-idiotypic antibodies raised against antibodies to RBP bound specificanly to rat intestine epithelial cells, which have a physiological cell-surface receptor for RBP. The RBP receptor mediates the uptake of retinol from RBP to the cells. This uptake was abolished in a concentration-dependent manner by the anti-idiotypic antibodies, which obviously competed with RBP for binding to the receptor.Anti-idiotypic antibodies against antibodies to insulin inhibited the binding of "25I-labeled insulin to isolated rat epididymal fat cells, whereas anti-idiotypic antibodies raised against antibodies to RBP had no effect. Furthermore, on interacting with young rat thymocytes, anti-idiotypic antibodies against antibodies to insulin stimulated the uptake by the cells of aaminoisobutyric acid, thereby mimicking the effect of insulin.These results suggest that in some cases anti-idiotypic antibodies may be useful tools in elucidating structure-function relationships for cell-membrane receptors. The immune system recognizes foreign substances by generation of antibodies that display an almost endless variety of combining sites. Thus, even a small, chemically well-defined molecule may, on immunization, give rise to stimulation of about 100 antibody-forming clones. Each clone produces a specific antibody with a unique amino acid sequence in the variable region (1). Due to the enormous variability in the antibody population, it seemed possible that among all the different antibodies that are elicited as a result of the immunization with, e.g., a hormone, a few antibodies might recognize that hormone in a fashion that mimics the way a physiological receptor recognizes the hormone. If so, the combining sites of such receptor-like antibodies might display structural features in common with the hormone-binding part of the receptor. Consequently, a few of a second set of antibodies raised against the combining sites, the idiotopes, of the "receptor-like" antibodies may, in their variable portions, be similar to those structures of the hormone that bind to the physiological receptor. Among such second sets of antibodies, anti-idiotypic antibodies, some would presumably interact with the hormone receptor in a hormone-like fashion.To test the above reasoning we have raised anti-idiotypic antibodies against antibodies to retinol-binding protein (RBP) and to insulin. Since cell-surface receptors for RBP (2) and insulin (for a review, see ref. 3) exist, the possible binding of the anti-idiotypic antibodies to these receptors has been explored. This communication presents data that demonstrate that such anti-idiotypic antibodies may become useful tools in elucidating the structure and function of cell-surface receptors.The costs of publication of this article...

The major human and murine histocompatibility antigens are tetrameric molecules with an apparent molecular weight of about 130,000. They are composed of two types of polypeptide chains. The two light chains, previously identified as 6B2-microglobulins, are bound to the two heavy, alloantigenic HL-A or H-2 polypeptide chains by noncovalent interactions only. The heavy chains are held together by disulfide bridge(s) located in the part of the molecule that is attached to the cell membrane.By limited proteolysis of the histocompatibility antigens evidence was obtained suggesting that the heavy chain may consist of three compact domains connected by more extended stretches of polypeptide chain. Each domain appeared to contain a single disulfide bridge encompassing about 60 to 70 amino-acid residues.Staphylococcus aureus protein A is known to bind exclusively to the Fc region of immunoglobulin G. It was, however, observed that protein A interacts in a similar way with the H-2 antigen heavy chain. This observation, together with the homology of the primary structure of ,62-microglobulin to immunoglobulin G, the tetrameric structure of the alloantigens, the organization of the heavy polypeptide chain into compact domains, and the presence of a single, immunoglobulin-like disulfide loop in each domain, establishes a close similarity in structure between histocompatibility antigens and immunoglobulins. The similarity in structural features suggests a common evolutionary origin of the two types of molecules.

The turnover of beta 2-microglobulin, the common subunit of the HLA antigens, has been examined in normal subjects and in some patients with kidney disorders, multiple myeloma and rheumatoid arthritis. All patients displayed elevated serum levels of beta 2-microglobulin. The plasma disappearance curve of 125I-beta 2-microglobulin demonstrated that the protein has a rapid turnover (t 1/2 = 2.1 h; range 1.1-2.8 h) in normal persons and in patients with a normal glomerular filtration rate. In patients with kidney disorders the impaired renal filtration prolonged the turnover time and led to elevated serum levels of beta 2-microglobulin. Simultaneous measurements of 125I-beta 2-microglobulin in serum and urine allowed estimations of the beta 2-microglobulin net reabsorption in the renal tubuli. Two patients with renal disease reabsorbed 84% and 89%, respectively, of the beta 2-microglobulin filtered in the glomeruli. In normal persons the net reabsorption is close to 100%. In patients with normal kidney function increased serum levels of beta 2-microglobulin seem to be due to an increased synthetic rate of the protein as the elimination rate is normal. HLA antigen heavy chains in serum are present in smaller amounts than beta 2-microglobulin. The present data, therefore, suggest an imbalanced synthesis of the two chains.

The turnover of /12-microglobulin, the common subunit of the HLA antigens, has been examined in normal subjects and in some patients with kidney disorders. multiple myeloma and rheumatoid arthritis. All patients displayed elevated serum levels of /1:-microglobulin. The plasma disappearance curve of '2sI-fl?microglobulin demonstrated that the protein has a rapid turnover (t!=2.1 h; range 1.1-2.8 h) in normal persons and in patients with a normal glomerular filtration rate. In patients with kidney disorders the impaired renal filtration prolonged the turnover time and led to elevated serum levels of /lz-microglobulin.Simultaneous measurements of '~sl-~~-microglobulin in serum and urine allowed estimations of the microglob globulin net reabsorption in the renal tubuli. Two patients with renal disease reabsorbed 84% and 89:<, respectively. of the j,-microglobulin filtered in the glomeruli. In normal persons the net reabsorption is close to 100%.In patients with normal kidney function increased serum levels of j32microglobulin Seem to be due to an increased synthetic rate of the protein as the elimination rate is normal. HLA antigen heavy chains in serum are present in smaller amounts than /$-microglobulin. The present data, therefore, suggest an imbalanced synthesis of the two chains.