Antigenic determinants common to human immunoglobulins G and M: importance of conformational antigens

Evaluation of monoclonal antibodies with specificity for human IgA, IgA subclasses and allotypes and secretory component. Results of an IUIS/WHO collaborative study

51 monoclonal antibodies (McAb) with putative specificity for human IgA, the IgA subclasses, Am allotypes or secretory component (SC) were evaluated for immunoreactivity and specificity by nine laboratories employing immunodiffusion, agglutination, immunohistological assays, immunoblotting and direct binding and competitive inhibition enzyme immunoassays. McAbs specific for IgA PAN (n = 24), IgA1 (n = 7), IgA2 (n = 3), IgA2m(2) (n = 2), non-IgA2m(2) (n = 4) and SC or secretory IgA (n = 5) were identified that were immunoreactive and specific in the assays employed. The McAbs identified as IgA- or SC-reactive were shown to be non-reactive to human IgG, IgM, IgD, IgE, kappa and lambda by direct binding and competitive inhibition immunoassays. Interestingly, no McAbs with restricted specificity for IgA2m(1) were identified. Some McAbs displayed higher affinity and/or better performance in one or several of the assay groups. The IgA- and SC-specific McAbs identified in this international collaborative study have potential as immunochemical reference reagents to identify and quantitate monomeric and polymeric IgA in human serum and secretions.

Antigenic determinants of heavy chain variable regions: immumological typing of the human immunoglobulin VHIII subgroup

An antigenic determinant of the VHIII variable region subgroup was defined by means of a heterologous specific antiserum using a hemagglutination inhibition procedure. The specificity of this antiserum was established in inhibition experiments with proteins either of known primary structure or belonging to a definite VH subgroup. A series of IgG, IgA, IgM and IgD monoclonal proteins was examined for the presence of this VHIII subgroup antigenic determinant. The data showed that 50% of the IgG, 62% of the IgA, 55% of the IgM and 41% of the IgD were VHIII-positive, and that certain "blocked" monoclonal immunoglobulins belonged to this subgroup. A preferential association of the VHIII antigenic determinant with the IgG1 and IgG3 subclasses was observed among IgG myeloma proteins while the preferential association was only observed with the IgG1 subclass when anti-Rh antibodies were studied. The VHIII subgroup exhibited nonallelic behavior.

Studies on fd fragments of human immunoglobulins. III. Immunogenic properties of gamma chains, myeloma fd gamma, and myeloma fd1 alpha

Earlier studies on antisera against Fab of pooled human IgG and IgA myeloma proteins disclosed the presence of class-specific Fd antibodies, the demonstration of which required interaction of heavy and light chains. To extend our knowledge about the antigenic structure of the Fd fragment of human immunoglobulins, antisera were prepared in rabbits against gamma chains of pooled IgG and of four IgG1 myeloma proteins, and Fd gamma fragment and a cyanogen bromide-produced CH1 preparation of an IgG1 myeloma protein, and an Fd' alpha fragment of an IgA1 myeloma protein. No antigenic determinants exclusively confined to the CH1 region of intact human IgG could be demonstrated with these antisera. The antigenic structure of CH1 intact immunoglobulins may thus only be defined by light-chain-dependent determinants.

Immunochemical studies in four cases of alpha chain disease

Studies of a number of properties of the pathological gammaA-proteins in the first four cases of the recently recognized alpha-chain disease demonstrate that, as in gamma-heavy-chain disease, the abnormal protein is devoid of light chains and represents a portion of the alpha-heavy chain related to the Fc-fragment. In two patients, serum electrophoresis showed a broad abnormal band, whereas in the two others the pathological protein was not noticeable on the electrophoretic pattern. The diagnosis of alpha-chain disease can be established without purification of the protein by immuno-electrophoresis and gel diffusion experiments using selected antisera to gammaA and a reference alpha-chain disease protein. All four proteins belonged to the alpha1-subclass, displayed electrophoretic heterogeneity, and showed a strong tendency to polymerize. The polymers occurred in vivo and were held together both by disulfide bonds and by strong noncovalent forces. Two of the three purified proteins had a very high carbohydrate content. The abnormal protein was always found in concentrated urines in variable but generally low amounts. It was not detected in parotid saliva but was present in significant amounts in jejunal fluid of all four patients. The alpha-chain disease protein was shown to be associated with the secretory piece in external secretions of two patients. The clinicopathological features were strikingly similar in the four patients. All patients were affected with a neoplastic and mostly plasmacytic proliferation involving primarily the whole length of the small intestine and the mesenteric nodes and all exhibited a severe malabsorption syndrome. While Israeli authors have emphasized the frequency of this type of abdominal lymphoma in young Arabs and non-Ashkenazi Jews, two of our patients were Kabyles, one a Syrian Arab, and one an Eurasian. Cellular studies showed that the pathological protein was synthesized by the proliferating cells in the lymphoid tissue of the digestive tract and in the mesenteric nodes, and that there was no detectable light-chain synthesis at the intracellular level.

Alpha-chain disease: a new immunoglobulin abnormality

A new type of pathological immunoglobulin was found in the serum, urine, and saliva of a young Arab patient with abdominal lymphoma and diffuse lymphoplasmacytic infiltration of the small intestine. This protein is devoid of light chains and is closely related to the alpha polypeptide chains of the gamma(A1) (Le) subclass of immunoglobulin A. It is characterized by electrophoretic heterogeneity, tendency toward polymerization, and a high carbohydrate content. No intracellular synthesis of light chain was detected.

Papain digestion fragments of human IgM globulins

Papain digestion of two Waldenström IgM globulins produced a high amount of small peptides and resulted in the formation of two end products, the Fabmicro and Fcmicro fragments. The Fcmicro fragment is characterized by a fast electrophoretic mobility, a high content in carbohydrate, and a high molecular weight. It was demonstrated that this fragment is made of heavy chain pieces belonging to several disulfide-linked monomeric subunits, presumably representing the carboxy-terminal end of the micro-chains. Fc fragments from the two macroglobulins could not be distinguished immunologically. An appreciable proportion of IgM molecules apparently underwent degradation without the formation of a stable Fc fragment. An Fc-like fragment, analogous to the reduced Fc fragment, was obtained at early stages of papain digestion of the IgM subunits. The Fabmicro fragment, with slow and individually distinct electrophoretic mobility, bears many physicochemical and immunological similarities to the Fabgamma fragment. It consists of one light chain and one Fd piece, both of which were isolated. The interaction of these two constituents was demonstrated by gel diffusion studies. Fab fragments of both IgM globulins were resolved into two subpopulations with different electric charges. In addition to these fragments, intermediary split products were observed at early stages of the degradation process, together with a high yield of small peptides mainly derived from the papain-sensitive region of the heavy chains. Immunologic data strongly suggested that this segment of micro-chains is situated between the Fd piece and the portion included in the Fc fragment. Several experiments indicated the importance of conformational antigenic specificity in both Fab and Fc regions of the IgM globulins.

Antibodies to native and denatured deoxyribonucleic acid in systemic lupus erythematosus

The relative reactivities with native and denatured DNA of 35 lupus sera were investigated by quantitative complement fixation and precipitin studies and showed great variations. The use of purified native DNA demonstrated that, in at least 22 of these 35 sera, the anti-DNA antibodies reacted with the native form, independently of denatured contaminants. Systemic lupus sera were shown to contain three main types of DNA antibodies: those reacting only with denatured DNA, those reacting to the same extent with both forms of DNA, and those reacting preferentially with native DNA. In some instances, the latter antibodies fix complement and precipitate only with native DNA but are inhibited by the denatured form. This finding points to the importance of conformation in the antigenic structure of DNA. The simultaneous occurrence of different varieties of DNA antibodies was demonstrated in several sera. Evidence was obtained that some of these human antibodies to DNA can belong to the IgM class. Thus, DNA antibodies from systemic lupus patients differ in many respects from most of the experimentally produced antibodies capable of reacting with DNA.