A variable region subclass of heavy chains common to immunoglobulins G, A, and M and characterized by an unblocked amino-terminal residue

Immunoglobulin evolution: chemical study of clawed toad (Xenopus laevis) heavy and light chains

NH2 terminal amino acid sequence determinations of clawed toad (Xenopus laevis) immunoglobulins indicate that approximately 30% of the heavy chains and less than 5% of the light chains have unblocked NH2 termini. The major amino acid sequence of the X. laevis 7S immunoglobulin heavy chains is the same as that of the 19S immunoglobulin heavy chains. Thus in the synthesis of the heavy chains, the VH genes coding for unblocked heavy chains can associate with CH genes of both the 19S and 7S classes. This association is particularly important in amphibians because, in contrast to mammals and birds, the majority of amphibian antibody-producing cells synthesize both 19S and 7S immunoglobulins and do not participate in the 'genetic switch' characteristic of lymphocyte differentiation in higher organisms. In X. laevis, the major amino acid sequence at the first twenty-four positions of the unblocked heavy chains shows approximately 54% difference from the prototype amino acid sequence of the mammalian VHIII subgroup. Thus, the VHIII gene(s) must have started to appear after the evolutionary divergence of the common ancestor of mammals and birds from the amphibian line. The amino acid composition of the X. Laevis 7S immunoglobulin heavy chains differs from that of its 19S immunoglobulins as well as those of human IgG and IgA. These data support the concepts (a) that amphibian 7S and 19S immunoglobins belong to distinct classes and (b) that amphibian 7S immunoglobulin does not resemble mammalian IgG or IgA.

Variable-region subgroup and specificity of cold agglutinins

The variable-region subgroup determined by amino acid sequence analysis of heavy and light chains of two monoclonal cold agglutinins with the new anti-Gd specificity is reported. Both proteins belong to the VHIII subgroup of heavy chains; one light chain falls into the V kappaI subgroup, the other has a blocked N-terminus which so far has not been observed in human kappa chains. The comparison of anti-Gd with anti-I/-i or anti-Pr cold agglutinins indicates that anti-Gd differs from other cold agglutinins with respect to variable-region subgroup. The data extend previous findings on the restriction of certain antibodies to distinct variable-region subgroups.

Human and murine phosphorycholine-binding immunoglobulins: conserved subgroup and first hypervariable region of heavy chains

The NH2-terminal 36 residues of the heavy chain and the NH2-terminal 40 residues of the light chain from a human Waldenström's IgM with binding activity for phosphorylcholine (phosphocholine) are compared with the published sequences of five mouse IgA myeloma proteins with the same activity. An extensive structural similarity; i.e., 3 amino acid interchanges within framework residues, and one in the hypervariable region, is noted between the heavy chains of both species. The light chains, however, show a considerable diversity and, in contrast to the heavy chain, no correlation between the primary structure of the first hypervariable region and the binding specificity is apparent. The finding of a very similar heavy chain variable region in two different species that are separated by about 75 million years in evolution favors the concept of stable transmission of variable region genes throughout evolution.

The amino-terminal sequence of the VHIII subgroup of pooled porcine IgG

Pig gamma-chains contain a significant fraction of the unblocked VHIII variable region subgroup. The amino terminal sequence (30 residues) was found to be uniform and more than 90% homologous with the prototype sequence of the human VHIII subgroup. An additional VHIII phylogenetically associated residue, glutamic acid in position 2 was identified in these porcine heavy chains.

Chemical and genetic characterization of a monoclonal IgA(lambda) protein with both cryo- and pyro-precipitability

Studies of a monoclonal IgA (lambda) protein with both cryo- and pyro-precipitability show that it belongs to the IgA2 subclass and is positive for the A2m(2) allotypic marker. Like other cryoglobulins, this protein also has an unblocked light chain, and its heavy chain belongs to the VHI subgroup. The first 22 N-terminal amino acids of the lambda chain of this protein showed less than 65% homology with those of other human lambda chains but showed 86% identity with that of an amyloid fibril protein reported by others. The alpha chain of this protein appears to have more glutamic acid or glutamine, or both, and less isoleucine residues than other human alpha chains.

N-terminal amino acid sequence of a human delta-chain myeloma protein

The N-terminal amino acid sequence (26 residues) of a delta-chain of a human myeloma (Er I) is homologous with the prototype sequence of the human VHIII subgroup. This indicates that the delta-chain is using for its V region the same pool of V genes as the rest of the immunoglobulin classes. Implications of this finding are discussed.

Cross-reactivity patterns of IgM and IgG anti-lipopolysaccharide antibodies in individual mice

A sensitive method has been developed which permits comparative analysis of IgM and IgG antibody specificity against lipopolysaccharide (LPS) antigen. It is based on hemolysis of LPS-coated red blood cells and on its inhibition by homologous and heterologous LPS. By appropriate use of anti-immunoglobulin sera, indirect (facilitated) lysis due to IgG antibodies is obtained, whereas IgM gives direct lysis and is 2-mercaptoethanol-sensitive. IgG can be analyzed either by facilitation with a rabbit anti-mouse Ig or with anti-allotype sera. By use of anti-allotype sera in F1 hybrids, both parental antibody types can be studied separately. Antibodies of either class from individual mice may display different cross-reactivity patterns. Furthermore, for IgM and IgG within a given serum, both similarities and differences have been found. Some of the cross-reactivity patterns have been followed over one year. With few exceptions, individual patterns remained constant throughout this period.

Partial characterization of the shift from IgG to IgA synthesis in the clonal differentiation of human leukemic bone marrow-derived lymphocytes

An unusual B-cell proliferation was noted in an individual (Tun) which was characterized by the presence of two separate populations of chronic lymphocytic leukemia (CLL) cell staining on the surface and in the cytoplasm for either IgG(k) or IgA(k). Utilizing an idiotypic antiserum prepared from the associated serum monoclonal IgG(k) protein the idiotype was detected on the surface and in the cytoplasm of both the IgG- and IgA-bearing cell populations. These observations are consistent with a common clonal origin and a switch mechanism involving IgG and IgA synthesis. Sequential-labeling of Surface Ig and intracellular Ig with antisera conjugated to opposite fluorochromes documented the progressive maturation of the terminal differentiation of the IgA-bearing cell population at a level before morphologically distinct plasma cells. The distribution and pattern of surface and cytoplasmic IgG and IgA staining in individual cells suggest that the direction of switching is from IgG to IgA synthesis. The demonstration of shared idiotypic specificity between the IgG- and IgA-bearing populations is consistent with a transition in Ig heavy chain synthesis resulting from an alternation in the CH gene. It is concluded that certain CLL clones may manifest a switch from IgG to IgA synthesis at a level of B-cell differentiation which encompasses both the B lymphocyte and the Ig-synthesizing plasma cell.

Similar specificity of IgG1 and IgG2a antibodies in individual mice

In this study the previous finding of similar variable regions in individual IgG1 and IgG2a antibody populations is extended by the demonstration of similar fine specificity of IgG1 and IgG2a combining sites. Antibody populations from individual mice directed against oligo-D-alanine determinants were analyzed in their cross-reactivity towards 5 heterologous dipeptides. This was done by mixing antibody and hapten followed by determination of free antibodies in a kinetic red cells sensitization assay. The comparison of hyperimmune sera from 10 mice showed that genetically identical mice can differ significantly in their cross-reaction pattern. Within each serum the cross-reaction pattern was determined for IgG1 and IgG2a. With a few exceptions the same individual pattern was found in both IgG1 and IgG2a antibody populations. This was taken as evidence that the combining sites of IgG1 and IgG2a anti-oligo-D-alanine antibody populations in an individual mouse are similar.

A cyclical appearance of antibody-producing cells after a single injection of serum protein antigen

After a single intravenous injection of rabbits with aggregated HuIgG, IgM- and IgG-plaque-forming cells (PFC) in both the spleens and peripheral blood of rabbits peaked 5, 13, and 21 days after injection, while almost no PFC could be detected on days 8 and 16. The available data suggest that the secondary peaks of PFC (days 13 and 21) resulted from stimulation of memory cells by persisting antigen that was localized in the germinal centers in the spleen. No such persistence of antigen occurred in the lymph nodes, and these lymphoid tissues did not exhibit secondary peaks of PFC. The identical kinetic patterns for IgM- and IgG-PFC indicate that the major portion of IgG-PFC did not result from IgM-secreting cells switching to IgG synthesis and secretion. The present data suggest that the antibody produced and present at the site of interaction between committed cells and antigen is responsible for the regulation of antibody synthesis to persisting antigens. Possible cellular events involved in both the regulation and an apparent synchronous appearance of antibody producing cells in the spleens of rabbits were presented.

Complete amino acid sequence of the Mu heavy chain of a human IgM immunoglobulin

The amino acid sequence of the micro, chain of a human IgM immunoglobulin, including the location of all disulfide bridges and oligosaccharides, has been determined. The homology of the constant regions of immunoglobulin micro, gamma, alpha, and epsilon heavy chains reveals evolutionary relationships and suggests that two genes code for each heavy chain.

Phylogenetically associated residues within the VH3 subgroup of several mammalian species. Evidence for a "pauci-gene" basis for antibody diversity

Immunoglobulin heavy chains from IgG pools of several mammalian species have been subjected to Edman degradation on an automated protein sequencer. The percentage of unblocked vs. blocked heavy chains was estimated from the yield of the invariant valine in the second position. Further analysis of these unblocked polypeptides unequivocally placed them in the V(HIII) subgroup on the basis of homology with known human heavy chain sequences. The mammals studied could be divided into three distinct categories on the basis of the distribution of the V(HIII) subgroup. In several species the V(HIII) subgroup could not be detected while, in others, virtually all of the heavy chains belonged to this subgroup. Several species had intermediate amounts with the level of the V(HIII) subgroup restricted to between 19 and 29% of the total pool. Within experimental error, all members of a given order had a similar V(HIII) subgroup distribution. Further amino acid sequence studies illustrated a high degree of structural homogeneity in the heavy chains of IgG isolated from pooled sera of a number of mammalian species. The very close amino acid sequence homologies of the amino terminal 24 residues of the various pools corroborated conclusions previously obtained using several myeloma proteins from some of these same species. In particular, certain phylogenetically associated residues were identifiable at characteristic positions in the pools in confirmation of their identification in the myeloma proteins. The simplest assumptions would suggest that these findings are more compatible with a pauci-gene than a multi-gene basis for the generation of antibody diversity.

Monoclonal production of both IgM and IgG1 antihapten antibody

The anti-DNP antibodies produced by primary and secondary splenic foci were analyzed for heavy chain class by a radioimmunoassay, using iodinated, purified goat antimouse micro-chain antibody and goat antimouse gamma1 chain antibody. The frequency of primary and secondary foci producing both IgM and IgG1 anti-DNP antibody (16% and 14%, respectively) was considerably higher than that which would be predicted by a random distribution. It would thus appear that IgM and IgG1 antibody can be made by the clonal progeny of a single precursor cell.

Localization of antibody-combining sites within the variable portions of heavy and light chains

The Fab'-fragment of a mouse IgA-myeloma (protein-315) was split by pepsin to yield a smaller fragment that retained the anti-2,4-dinitrophenyl activity of the intact protein. This fragment, which we call Fv, has a molecular weight of about 30,000 (half that of Fab'), and is composed of two polypeptide chains (molecular weight 14,000) held together by noncovalent bonds. The N-terminal sequence of Fv suggests that it is composed of the N-terminal half of Fab', and consists of the variable portions of the heavy and light chains. Since Fv has about one binding site with the same association constant as Fab', this experiment provides direct evidence that the antibody site in this protein is contained entirely in the variable portion, and is independent of the constant portion, of the molecule.

The complete amino acid sequence of a mouse kappa light chain

The complete amino acid sequence of the kappa-chain of the mouse myeloma protein MOPC 21 was established. The protein was reduced and alkylated with iodo[2-(14)C]acetic acid, and 21 tryptic peptides were isolated, mainly by paper electrophoresis and paper chromatography. Three large tryptic peptides (of 35, 36 and 42 residues), which were difficult to isolate in this manner, were obtained pure and in excellent yields by a combination of Sephadex G-50 gel filtration in 1% (w/v) NH(4)HCO(3) and chromatography on a DEAE-cellulose column in ammonium acetate buffer, pH8.1. Peptides overlapping the tryptic peptides were isolated from a chymotryptic digest. The chain is 214 residues long. Microheterogeneity of two peptides was observed and is believed to be due to deamidation. It was not excluded that such deamidation could occur in serum from which the protein was isolated. The sequence is compared with the sequences of two other mouse kappa-chains, and with the human kappa-chain basic sequences.

The disulphide bridges of a mouse immunoglobulin G1 protein

[(35)S]Cystine-labelled immunoglobulin MOPC21 (IgG1) was prepared from myeloma cells in tissue culture. Carrier myeloma protein was added and the protein was digested with pepsin. The digest was fractionated on Sephadex G-50 into two fractions, further digested with trypsin and again fractionated on Sephadex. Disulphide-bridge peptides were purified by electrophoresis and chromatography and identified by radioautography. A peptide of 96 residues was isolated, which contains both the heavy-light interchain disulphide bridge and all the inter-heavy-chain disulphide bridges. Other peptides were isolated, accounting for all the intrachain disulphide bridges (which could be placed by homology with proteins of other species), except for the variable section of the light chain. Sequences describing this missing disulphide bridge were obtained from totally reduced and alkylated light chains. Peptides related to the interchain disulphide-bridge peptide were isolated from partially reduced and alkylated myeloma protein and from totally reduced heavy chain. The interchain disulphide-bridge peptide was placed at the C-terminal position of the F(ab')(2) fragment, prepared by digestion of the protein with pepsin at pH4.0. Sequences from the heavy-chain intrachain disulphide bridges of MOPC 21 immunoglobulin are compared with homologous sequences from mouse myeloma proteins of other subclasses and proteins of other species.

N-terminal amino-acid sequence of African lungfish immunoglobulin light chains

The sequence of the N-terminal ten amino acids of the unblocked light chains derived from the low molecular weight immunoglobulin of a dipnoid fish, the African lungfish (Protopterus aethiopicus), has been determined. A degree of sequence heterogeneity as extensive as that displayed by pooled mammalian light chains was encountered. The major N-terminal sequence of the amino acids of light chains from lungfish immunoglobins can be made homologous with that of various Elasmobranchean, Chondrostean, Avian, and Mammalian species if an internal deletion of two base triplets in the gene coding for light chains from lungfish immunoglobulins is assumed. The existence of a deletion and/or insertion mechanism may have profound biological significance, since it would be ideal for the introduction of variability into immunoglobulin chains without sacrificing certain integral features of the antibody molecule.

Variation and homology in the mu and gamma heavy chains of human immunoglobulins

Sequence analysis of an 1gM immunoglobulin shows that the variable regions of hunman micro and gamma1 heavy chainis may have twice as much homology as their constant regions and that evolutionary divergence of micro and gamma1 heavy chain genes occurred not long after the separation of heavy and light chain genes.

Primary immunodeficiencies

Increased understanding of the nature and variety of immunodeficiency states in man is rapidly accumulating both from studies of human patients and from experimental work on the immune response in animals. Progress is evident in the development of diagnostic tests for deficiencies in both humoral and cellular mechanisms of immunity, and in the introduction of new forms of therapy-for example, the grafting of lymphoid cells. Studies of immunodeficiency provide the most direct evidence concerning the nature of the immune response in man, and hence are of wide general interest. In this paper, current knowledge and concepts are summarized, a logical classification is presented, and recommendations are made for the investigation and treatment of these disorders.