Noncovalent interaction between immunoglobulin (Ig) polypeptide chains. II. Absence of hybrid molecule formation between Ig Classes.
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Biomedical subjects
Publications and source records attributed to H M Grey.
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The gammaA2 globulins have attracted considerable interest because of the absence of the disulfide bonds linking the heavy and light chains characteristic of all other human immune globulins. Recently a genetic marker (Am(2)) has been found which delineates two genetic variants of gammaA2 globulins that are controlled by allelic genes. These differ markedly in incidence in different populations with a marked preponderance in Caucasians of the type possessing the Am(2) marker. A study of 22 gammaA2 myeloma proteins primarily from Caucasians showed that 20 were Am(2)(+), and 2 were Am(2)(-). All of the positive type dissociated in the presence of acid or urea into heavy and light chain dimers without reduction of disulfide bonds, as expected from the earlier studies. However, the two Am(2)(-) proteins failed to dissociate in the presence of acid, urea, guanidine, or detergent. It was only after partial reduction and alkylation that these molecules split into heavy and light chains. Thus the unique absence of disulfide bonds linking the heavy and light chains is a property of only one genetic variant and not of all gammaA2 proteins.
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The gammaA2-subgroup of gammaA-globulins, previously delineated by antigenic studies, was found to differ strikingly from other immunoglobulins in the manner in which the polypeptide chains are bound together. The heavy and light chains were not linked to each other by disulfide bonds. Instead the light chains were disulfide linked to one another, and were present in the gammaA2-molecule as disulfide bridged L-L dimers. Antisera specific for gammaA2-proteins indicated the occurrence of two different antigenic types in all normal sera as well as saliva and colostrum. Both of these showed the unique interchain disulfide linkage. Quantitative analyses indicated higher levels of gammaA2-proteins in external secretions.
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Seven human gammaG-myeloma proteins which were also cryoglobulins were studied with respect to their reactivity with gammaG-globulins as well as with regard to their antigenic classification within the gammaG-heavy chain subclasses. Five of the seven cryoglobulins studied were positive in at least two of the three tests used to assay for anti-gamma-globulin activity. One protein was only weakly positive in one test system and another was negative in all test systems. The structures which were recognized by the cryoglobulins were localized to the Fc-fragment. Only primate gammaG-globulins contained these antigenic determinants and in some cases the cryoglobulin appeared to show specificity for one human heavy chain subclass over the others. Antigenic analysis revealed that four of the five cryoglobulins with definite antibody activity belonged to the gammaG3-subclass, the fifth belonged to the gammaG1-subclass. The two cryoglobulins which reacted only weakly or failed to combine with gammaG-globulins were both of the gammaG1-subclass. These findings taken together with the localization of the combining site to the Fab-fragment suggests that many of these cryoglobulins may represent antibodies to gammaG-globulin, and that the cryoprecipitate in these cases represents antigen-antibody complexes of such a nature that they precipitate only in the cold.
The rates of catabolism of human gammaG-immunoglobulins of subclasses gammaG(1), gammaG(2), gammaG(3), and gammaG(4) were studied by determining the rates of elimination from the circulation of pairs of (131)I-and (125)I-labeled gammaG-myeloma proteins in 57 patients suffering from cancer other than multiple myeloma. On the average, gammaG(1)-, gammaG(2)-, and gammaG(4)-myeloma proteins were catabolized at a rate similar to that of normal gammaG-immunoglobulin, whereas gammaG(3)-myeloma proteins were catabolized more rapidly than normal gammaG-immunoglobulin. The average half-lives for the myeloma proteins were 12.3 days for normal gammaG, 11.6 days for gammaG(1), 12.4 days for gammaG(2), 8.2 days for gammaG(3), and 11.3 days for gammaG(4). However, significant differences in catabolic rates were observed when individual myeloma proteins of a single subclass were compared. These individual variations were present within all four heavy chain subclasses. The extent of differences ranged from 10 to 47%. The catabolic rate of normal gammaG was in an intermediate range when compared with myeloma proteins of relatively long and short half-lives. The rate of catabolism of an individual myeloma protein did not correlate with its light chain type, Gm factor, carbohydrate content, or electrophoretic mobility. These findings indicate that the structure(s) related to the catabolism of gammaG-immunoglobulins are complex and differ from one immunoglobulin molecule to another.
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