"Alpha chain disease" protein def: internal deletion of a human immunoglobulin A1 heavy chain

Sequence composition predicts immunoglobulin superfamily members that could share the intrinsically disordered properties of antibody CH1 domains

Antibodies are central to the growing sector of protein therapeutics, and increasingly they are being manipulated as fragments and combinations. An improved understanding of the properties of antibody domains in isolation would aid in their engineering. We have conducted an analysis of sequence and domain interactions for IgG antibodies and Fab fragments in the structural database. Of sequence-related properties studied, relative lysine to arginine content was found to be higher in CH1 and CL than in variable domains. As earlier work shows that lysine is favoured over arginine in more soluble proteins, this suggests that individual domains may not be optimised for greater solubility, giving scope for fragment engineering. Across other sequence-based features, CH1 is anomalous. A sequence-based scheme predicts CH1 to be folded, although it is known that CH1 folding is linked to IgG assembly and secretion. Calculations indicate that charge interactions in CH1 domains contribute less to folded state stability than in other Fab domains. Expanding to the immunoglobulin superfamily reveals that a subset of non-antibody domains shares sequence composition properties with CH1, leading us to suggest that some of these may also couple folding, assembly and secretion.

An unfolded CH1 domain controls the assembly and secretion of IgG antibodies

A prerequisite for antibody secretion and function is their assembly into a defined quaternary structure, composed of two heavy and two light chains for IgG. Unassembled heavy chains are actively retained in the endoplasmic reticulum (ER). Here, we show that the C(H)1 domain of the heavy chain is intrinsically disordered in vitro, which sets it apart from other antibody domains. It folds only upon interaction with the light-chain C(L) domain. Structure formation proceeds via a trapped intermediate and can be accelerated by the ER-specific peptidyl-prolyl isomerase cyclophilin B. The molecular chaperone BiP recognizes incompletely folded states of the C(H)1 domain and competes for binding to the C(L) domain. In vivo experiments demonstrate that requirements identified for folding the C(H)1 domain in vitro, including association with a folded C(L) domain and isomerization of a conserved proline residue, are essential for antibody assembly and secretion in the cell.

Alpha heavy chain disease alpha mRNA contain nucleotide sequences of unknown origins

Human alpha heavy chain disease is characterized by the production of abnormally short alpha IgH chains. In previously published cases it has been found that the malignant cells produce abnormal alpha mRNA, lacking VH and CH1 sequences and composed of a leader sequence peptide, sequences of variable length (69 to 84 bp) and of unknown origin, followed by normal CH2 and CH3 sequences. In this study we established the nucleotide sequence of alpha mRNA for six cases of alpha heavy chain disease. We observed that all six alpha mRNA lack the VH and CH1 sequences as do those previously described. They also contain in-frame inserts of unknown origin between the leader peptide and the normal CH2 and CH3 coding sequences. These inserts are of variable length (42 to 105 bp) and they are unrelated. These results suggest the existence of a common mechanism defect leading to deletions/insertions in alpha heavy chain disease rather than a specific interaction between alpha 1 IgH gene with a unique defined molecular species.

Gastrointestinal lymphoma

Primary GI lymphoma is a rare clinical entity. A primary nodal tumor should be ruled out. Symptoms may not be localizing and B symptoms are less common. A tissue diagnosis, preferably by transmural biopsy for small intestinal involvement, often reveals a high-grade morphology. The staging work-up should include a bone marrow examination, although formal staging laparatomy is not always required. Patients with Mushoff stage IE or IIE1 disease do better than those with extraregional nodal disease or distant metastatic involvement. Surgical resection with clear margins is required in order to maximize the changes for cure. Chemotherapy or radiotherapy may give a survival advantage when used as adjuvant treatment for selected stage IE and IIE disease. Chemotherapy should be used after surgical debulking in more advanced disease in order to minimize the chance for bleeding or performation. Future randomized, multi-institutional trials will give more direction as to the best modes of management.

Distribution of antigenic determinants on human IgA1

The distribution of antigenic determinants on human IgA was studied with fragments and mutants of IgA1. F(abc)2 and Fabc, lacking the CH3 domain, F(ab')2 and Fab', lacking the CH2 and CH3 domain, Fab that further lacks most of the hinge region, and Fc fragments were included in our investigations. Antibodies specific for the CH3 domain of IgA1 were found in antisera raised against an alpha 1-HCD protein and in anti-Fc alpha antisera. The antisera detected different antigenic determinants on CH3 as was shown by inhibition with sera from nonhuman primates. An anti-Fc5 mu antiserum detected a determinant on Fc common to IgA and IgM. The serum of an IgA-deficient individual reacted with a determinant on CH2 of four-chain molecules only. A subclass-specific anti-Fabc antiserum detected a determinant which needed interaction of CH2 and CH1 or the hinge region. Anti-Fab antisera reacted with class or subclass specific determinants on CH1. The isoallotype nA2m(2) is probably located on CH1. Its expression requires two alpha-chains stabilized in a conformation attributed to by CH2.

Monoclonal IgM cryoglobulinemia associated with gamma-3 heavy chain disease: immunochemical and biochemical studies

A patient (Mia) with a monoclonal IgM(kappa) cryoglobulin (cryo IgM) developed additional heavy chain disease proteins of the gamma3 subclass 8 years later. Biochemical studies of the cryo IgM indicated that the heavy chain was VHI, but the NH2-terminal amino acid sequence of the light chain did not permit a definite assignment of its Vkappa subgroup. Two major fragments of the gamma3 chain were distinguishable by electrophoresis in sodium dodecyl sulfate polyacrylamide gel. The smaller component (designated Mia F) had a molecular weight of approximately 30 000 and the larger component (designated Mia S) 35 000. Both fragments had G3m(21) and G3m(27) allotypic determinants. These data and the NH2-terminal amino acid sequence of the gamma chain fragments suggested that Mia S consists of the major part of the gamma3 hinge region plus the CH2 and CH3 domains of the gamma3 chain, whereas Mia F may be derived from the former as a result of postsynthetic cleavage. The partial amino acid sequence of the Mia S fragment is homologous to the hinge region amino acid sequence of human gamma3 chains reported in the literature, with only one amino acid difference out of the 11 residues compared. This difference may represent an allotypic difference within the gamma3 subclass. Alternatively, the production of Mia S may have resulted from the accidental derepression of a "silent" constant region gene not expressed in normal individuals.

Immunobiology and pathogenesis of alpha chain disease

alpha chain disease, the most frequent of the heavy chain diseases, is a proliferative disorder of B lymphoid cells involving primarily the small intestine and mesenteric nodes. The characteristic immunoglobulin, whose detection by immunochemical techniques may present some difficulties, consists of incomplete alpha chains devoid of light chains. The deleted portion of the alpha chain is located in the Fd segment and involves both the variable and first constant domains. In both of two proteins for which structural data are available, normal sequence resumes at the beginning of the hinge region. The absence of L chains is due to a failure of synthesis. alpha chain disease appears to proceed in two stages. The early stage is characterized by a possibly non-malignant diffuse and extensive plasma cell infiltration which may be reversible after administration of antibiotics. The later stage is characterized by overt neoplasia (immunoblastic lymphoma). The socio-geographic distribution of the digestive form of alpha chain disease shows a clear predilection for underpriviliged populations living in areas with a high degree of infestation by intestinal pathogens which play presumably a crucial role in the pathogenesis of the disease.

Mu heavy-chain disease--a defect in immunoglobulin assembly. Structural studies of the kappa chain

Mu-chain protein GLI is a pentameric molecule with an amino-terminal deletion comprising 130 residues. The half-cysteine residue (position 140) which forms the H-L disulfide bridge in normal IgM is present. Instead of being joined to the L chain, it presumably exists as an additional inter-H-H disulfide bridge. The kappa Bence Jones protein is of normal size and present in two forms: as monomers and dimers. The carboxy-terminal half-cysteine of the monomer is bound to cysteine. Possible reasons for failure of assembly between mu and L chains are briefly discussed.

Alpha-chain disease and related small-intestinal lymphoma: a memorandum

Primary intestinal lymphomas are remarkably frequent in the Mediterranean region and South-West Asia. They are usually found in young persons from the lower socio-economic strata of the population. These conditions sometimes present a premalignant phase characterized by plasmacytic infiltration of the small intestine. It has been reported that early treatment of cases with antibiotics is followed by complete remission, suggesting that some environmental factors may be responsible for the disease. Some patients have an abnormal alpha-chain protein in their serum. This Memorandum reviews the present knowledge of the clinical, immunological, epidemiological, and therapeutic aspects of this condition.

Alpha chain disease: immunoglobulin abnormalities, pathogenesis and current concepts

The laboratory findings upon which the diagnosis of alpha chain disease relies and the main results of immunochemical, structural and biosynthetic studies of the pathological immunoglobulin are reviewed briefly. The pathogenesis of the disease is discussed in view of its possibly non-malignant nature at the early stage and of its peculiar geographic distribution, suggesting the triggering role of an intestinal micro-organism.

Differential susceptibility of human IgA immunoglobulins to streptococcal IgA protease

IgA protease, a proteolytic enzyme found in human saliva and colonic fluid, hydrolyzes human serum IgA immunoglobulins to yield Fab(alpha) and Fc(alpha) fragments. The enzyme is produced by organisms in the normal human microflora and can be purified from culture filtrates of the common human oral organism Streptococcus sanguis (American Type Culture Collection no. 10556). IgA protease is inactive against all other protein substrates examined including the other classes of human immunoglobulins. The role of this enzyme in affecting the function of the secretory IgA immune system is unknown. To further characterize and explain this unusual substrate specificity, the susceptibility of 31 human IgA myeloma proteins of both subclasses was investigated. 16 IgA1 and 15 IgA2 myeloma paraproteins were treated with enzyme and the extent of proteolysis was determined by cellulose actate electrophoresis, immunoelectrophoresis, polyacrylamide gel electrophoresis, and column chromatography. All IgA1 proteins were enzymatically cleaved to Fab(alpha) and Fc(alpha) fragments, but all IgA2 proteins were resistant, yielding no fragments after prolonged enzymatic treatment. N-terminal amino acid sequence analysis of the purified Fc(alpha) fragment of a single IgA1 paraprotein was as follows: Thr-Pro-Ser-Pro-?-Thr-Pro-Pro-Thr-Pro-Ser-Pro-Ser. Comparison of this sequence to that reported for the IgA1 heavy chain shows that the enzyme-susceptible peptide bond is a Pro-Thr in the IgA1 hinge region. The most likely explanation of the resistance of the IgA2 subclass to IgA protease is a deletion in the heavy chain which commences with the critical threonine of the susceptible Pro-Thr bond.