Structure and function of the J chain

Detection of Rare Objects by Flow Cytometry: Imaging, Cell Sorting, and Deep Learning Approaches

Flow cytometry nowadays is among the main working instruments in modern biology paving the way for clinics to provide early, quick, and reliable diagnostics of many blood-related diseases. The major problem for clinical applications is the detection of rare pathogenic objects in patient blood. These objects can be circulating tumor cells, very rare during the early stages of cancer development, various microorganisms and parasites in the blood during acute blood infections. All of these rare diagnostic objects can be detected and identified very rapidly to save a patient's life. This review outlines the main techniques of visualization of rare objects in the blood flow, methods for extraction of such objects from the blood flow for further investigations and new approaches to identify the objects automatically with the modern deep learning methods.

Bioinformatics Analyses Determined the Distinct CNS and Peripheral Surrogate Biomarker Candidates Between Two Mouse Models for Progressive Multiple Sclerosis

Previously, we have established two distinct progressive multiple sclerosis (MS) models by induction of experimental autoimmune encephalomyelitis (EAE) with myelin oligodendrocyte glycoprotein (MOG) in two mouse strains. A.SW mice develop ataxia with antibody deposition, but no T cell infiltration, in the central nervous system (CNS), while SJL/J mice develop paralysis with CNS T cell infiltration. In this study, we determined biomarkers contributing to the homogeneity and heterogeneity of two models. Using the CNS and spleen microarray transcriptome and cytokine data, we conducted computational analyses. We identified up-regulation of immune-related genes, including immunoglobulins, in the CNS of both models. Pro-inflammatory cytokines, interferon (IFN)-γ and interleukin (IL)-17, were associated with the disease progression in SJL/J mice, while the expression of both cytokines was detected only at the EAE onset in A.SW mice. Principal component analysis (PCA) of CNS transcriptome data demonstrated that down-regulation of prolactin may reflect disease progression. Pattern matching analysis of spleen transcriptome with CNS PCA identified 333 splenic surrogate markers, including Stfa2l1, which reflected the changes in the CNS. Among them, we found that two genes (PER1/MIR6883 and FKBP5) and one gene (SLC16A1/MCT1) were also significantly up-regulated and down-regulated, respectively, in human MS peripheral blood, using data mining.

Immunoglobulin A in Bovine Milk: A Potential Functional Food?

Immunoglobulin A (IgA) is an anti-inflammatory antibody that plays a critical role in mucosal immunity. It is found in large quantities in human milk, but there are lower amounts in bovine milk. In humans, IgA plays a significant role in providing protection from environmental pathogens at mucosal surfaces and is a key component for the establishment and maintenance of intestinal homeostasis via innate and adaptive immune mechanisms. To date, many of the dairy-based functional foods are derived from bovine colostrum, targeting the benefits of IgG. IgA has a higher pathogenic binding capacity and greater stability against proteolytic degradation when ingested compared with IgG. This provides IgA-based products greater potential in the functional food market that has yet to be realized.

IgM and its receptors: structural and functional aspects

This review combines the data obtained before the beginning of the 1990s with results published during the last two decades. The predominant form of the IgM molecule is a closed ring composed of five 7S subunits and a J chain. The new model of spatial structure of the pentamer postulates nonplanar mushroom-shaped form of the molecule with the plane formed by a radially-directed Fab regions and central protruding portion consisting of Cµ4 domains. Up to the year 2000 the only known Fc-receptor for IgM was pIgR. Interaction of IgM with pIgR results in secretory IgM formation, whose functions are poorly studied. The receptor designated as Fcα/µR is able to bind IgM and IgA. It is expressed on lymphocytes, follicular dendritic cells, and macrophages. A receptor binding IgM only named FcµR has also been described. It is expressed on T- and B-lymphocytes. The discovery of new Fc-receptors for IgM requires revision of notions that interactions between humoral reactions involving IgM and the cells of the immune system are mediated exclusively by complement receptors. In the whole organism, apart from IgM induced by immunization, natural antibodies (NA) are present and comprise in adults a considerable part of the circulating IgM. NA are polyreactive, germ-line-encoded, and emerge during embryogenesis without apparent antigenic stimuli. They demonstrate a broad spectrum of antibacterial activity and serve as first line of defense against microbial and viral infections. NA may be regarded as a transitional molecular form from invariable receptors of innate immunity to highly diverse receptors of adaptive immunity. By means of interaction with autoantigens, NA participate in maintenance of immunological tolerance and in clearance of dying cells. At the same time, NA may act as a pathogenic factor in atherosclerotic lesion formation and in development of tissue damage due to ischemia/reperfusion.

The IgA/IgM receptor expressed on a murine B cell lymphoma is poly-Ig receptor

T560, a mouse B lymphoma that originated in gut-associated lymphoid tissue, expresses receptors that bind dimeric IgA and IgM in a mutually inhibitory manner but have little affinity for monomeric IgA. Evidence presented in this paper indicates that the receptor is poly-Ig receptor (pIgR) known in humans and domestic cattle to bind both IgA and IgM. The evidence includes the demonstration that binding of IgM is J chain dependent, and that pIg-precipitated receptor has an appropriate Mr of 116-120 kDa and can be detected on immunoblots with specific rabbit anti-mouse pIgR. Overlapping RT-PCR performed using template mRNA from T560 cells and oligonucleotide primer pairs designed from the published sequence of mouse liver pIgR indicate that T560 cells express mRNA virtually identical with that of the epithelial cell pIgR throughout its external, transmembrane, and intracytoplasmic coding regions. Studies using mutant IgAs suggest that the Calpha2 domain of dimeric IgA is not involved in high-affinity binding to the T560 pIgR. Inasmuch as this mouse B cell pIgR binds IgM better than IgA, it is similar to human pIgR and differs from rat, mouse, and rabbit epithelial cell pIgRs that bind IgA but not IgM. Possible explanations for this difference are discussed. All clones of T560 contain some cells that spontaneously secrete both IgG2a and IgA, but all of the IgA recoverable from the medium and from cell lysates is monomeric; it cannot be converted to secretory IgA by T560 cells.

Reduced inhibition of Candida albicans adhesion by saliva from patients receiving oral cancer therapy

The effect of saliva on the adhesion of Candida albicans to epithelial cells was examined in vitro by using saliva from healthy controls and patients with oral squamous cell carcinoma. The adhesion of C. albicans to established epithelial tumor cells was reduced by 40% by salivary treatment of the C. albicans or epithelial cells. The inhibitory activity of saliva was almost completely abolished by anti-secretory immunoglobulin A antibody, concanavalin A, and mannose. Compared with saliva from healthy individuals, that from patients who had received chemoradiotherapy for oral carcinoma showed reduced suppression of C. albicans adhesion, which accompanied decreased salivary secretory immunoglobulin A and lactoferrin concentrations. A greater number of C. albicans cells adhered to buccal cells obtained from patients who had received chemoradiotherapy than to those from healthy individuals. Treatment of either epithelial cells or C. albicans with anticancer drugs induced an increase in adherence of epithelial cells and yeast cells. In contrast, concanavalin A- and mannose-pretreated C. albicans exhibited reduced adhesion to epithelial cells. No further decrease of C. albicans adhesion was observed when both epithelial cells and yeast phase C. albicans were treated with mannose. In conclusion, the inhibition of C. albicans adhesion by saliva depends largely on mannose residues on salivary glycoproteins and mannose is one of the binding ligands on both C. albicans and epithelial cells. In addition, anticancer therapy may induce oral C. albicans overgrowth by decreasing salivation and the concentrations of glycoproteins in saliva inhibiting C. albicans adhesion and by increasing the adhesive properties of both C. albicans and oral epithelial cells.

IgM hexamers?

There has been a universal tendency to regard IgM antibodies as pentameric molecules comprising five immunoglobulin monomeric subunits joined by a single J-chain protein. Is this the only form of secreted IgM, or are the possibilities more complex? In this article, Joseph Brewer and colleagues propose that the IgM polymers secreted in primary immune responses may be more heterogeneous than previously believed and that, as a consequence, the biological activity of IgM may have considerable flexibility.

Interaction between streptococcal protein Arp and different molecular forms of human immunoglobulin A

Protein Arp, the IgA-binding protein of the group A Streptococcus, has affinity for the Fc-part of IgA. The binding between protein Arp and several different molecular forms of human IgA was characterized. It was found that protein Arp bound with higher affinity to uncomplexed forms of IgA than to complexed forms (secretory IgA, alpha 1-antitrypsin-IgA and alpha 1-microglobulin-IgA). Thus, the affinity constant was 2.0-5.9 x 10(8) M-1 for the binding to monomeric, dimeric, trimeric, and quadrimeric IgA, and 4.5-5.0 x 10(7) M-1 for binding to the complexed forms. Among the uncomplexed IgA-molecules, the affinity constant was in the same range for J chain-containing forms (dimeric, trimeric and quadrimeric IgA) as for forms without J chain (monomeric and a particular quadrimeric IgA devoid of J chain). Western blotting demonstrated that protein Arp bound exclusively to the alpha-chain of all IgA-forms. Several lines of evidence pointed to a localization of the binding site to the C alpha 3-domain. First, protein Arp did not bind to three N-terminal alpha-chain fragments which lacked a region corresponding to the C alpha 3-domain, including that form a four-chain myeloma IgA, naturally occurring in plasma. Second, the binding to dimeric and tri/quadrimeric IgA was partially blocked by an added secretory component, which has been suggested to bind to the C alpha 2- and C alpha 3-domains of the alpha-chain. Finally, alpha 1-antitrypsin and alpha 1-microglobulin, in the weakly binding IgA-complexes, have been shown to be linked to the C alpha 3-domain via the penultimate amino acid residue of the alpha-chain peptide, supporting the hypothesis of a localization of the binding site of protein Arp to the C alpha 3-domain.

Aging-associated intrinsic defects in IgA production by murine Peyer's patch B cells stimulated by autoreactive Peyer's patch T cell hybridoma-derived B cell stimulatory factors (BSF)

Immune functions deteriorate with age, primarily as a result of alterations in the number and subpopulations of T cells of the immune system. In contrast, the B cell component of the immune system is generally affected by senescence only to a minor extent. In the present report, we stimulated murine Peyer's patch (PP) B cells by nonspecific multifunctional B cell stimulatory factors (BSF) secreted by one of several autoreactive (self-major histocompatibility complex (MHC)-class II antigen-responsive) T cell hybridoma clones derived from PP of syngeneic mature adult mice, and then determined in vitro whether aging-associated intrinsic defects could be demonstrated in the proliferation of, and the synthesis and secretion of mucosal IgA by, the BSF-activated B cells. This approach could be a useful new in vitro method for assessing the effect of senescence on B cell Ig production, especially that of IgA, in the gut-associated lymphoid tissue (GALT). Aged PP B cells stimulated by the autoreactive PP T cell-derived BSF proliferated more (P less than 0.05), contained larger amounts of IgA (nearly 10 times) and also secreted considerably more IgA (nearly 4.5 times) than did mature adult PP B cells. However, the ratio of intracellular dimeric (d) IgA to total IgA in the aged B cell lysates was significantly reduced (by approx. 44%) as was also the secreted dIgA (by approximately 50%). The augumentation of not only the proliferation, but also the synthesis and secretion of IgA in vitro along with reduced dIgA/total IgA ratios of BSF-stimulated aged PP B cells appears to be due to aging-related intrinsic defects. Alterations in intracellular regulatory mechanisms of B cells, mediated by B cell receptors for autoreactive T cell-derived BSF, could be largely responsible for the observed polyclonal B cell hyperreactivity, associated with senescence.

Studies on the relationships of IgA to human liver. IgA deposition in non-alcoholic liver diseases

An investigation was conducted to clarify the relationships of IgA to the human liver. Immunocytochemical studies were performed on biopsy specimens from patients with cirrhosis and chronic hepatitis without any apparent history of alcohol abuse. The results showed that 1) a large amount of IgA is associated with the sinusoidal surface of hepatocytes, endothelial cells and Kupffer cells, 2) this IgA contains J chain and can form a complex with secretory component, and 3) this mainly belongs to the IgA1 subclass, 4) IgA in vesicles within hepatocytes and Kupffer cells is always associated with acid phosphatase activity, and 5) IgA containing vesicles within ductular epithelial cells always lack such enzyme activity. We conclude that 1) the IgA bound to the surface of hepatocytes, sinus endothelial cells and Kupffer cells is polymeric IgA1 uncomplexed with SC, and 2) this IgA occasionally enters these cells, and may be degraded in the lysosomes. 3) Polymeric IgA combines with SC in the ductular epithelium and may be secreted into bile. These findings suggest that J chain-linked polymeric IgA bound to the surface of hepatocytes and Kupffer cells has a certain pathological significance in liver diseases and might be involved in the clearance of excess IgA from the circulation.

Secretory component and immunoglobulins in the intrahepatic biliary tree and peribiliary gland in normal livers and hepatolithiasis

Distribution of secretory component (SC), IgA, IgM and joining chain (J chain) in the intrahepatic biliary epithelium and peribiliary glandular epithelium were studied in normal livers and hepatolithiasis. In normal livers, SC was immunohistochemically demonstrated homogeneously in the cytoplasm of the biliary lining and peribiliary glandular epithelium. Immunoelectron-microscopically, SC was localized in the basolateral plasma membranes, nuclear membranes, rough endoplasmic reticulums, Golgi complexes and intracytoplasmic small vesicles, suggesting that the biliary lining and peribiliary glandular epithelium has an ability to synthesize SC. On the other hand, IgA and IgM were found heterogeneously in the biliary lining epithelium, and immunoelectron-microscopically they were only localized in the basolateral plasma membranes and vesicles. J chain was found in similar portions, suggesting that IgA and IgM in biliary lining and glandular epithelium were polymeric. It seems likely that polymeric IgA and IgM combine with SC on the biliary lining and glandular epithelial membranes, and subsequent endocytic transport and secretion of these complexes into the bile occur. In hepatolithiasis in which biliary living epithelia are hyperplastic and peribiliary glands proliferate markedly, such endocytic transport and secretion seemed to be increased. From these findings, it was suggested that the peribiliary glandular as well as biliary lining epithelium contributes to a local immunity in the biliary tree, especially in hepatolithiasis.

Strong association of bovine IgM with microvilli and their microfilament core from 13762 ascites tumor cells

Microfilament cores, obtained by extracting 13762 mammary ascites tumor cell microvilli with Triton X-100, contain a major glycoprotein migrating at an apparent molecular weight of 80 kDa by dodecyl sulfate-polyacrylamide gel electrophoresis. The 80-kDa component is a disulfide-linked multimer, as demonstrated by velocity sedimentation and agarose-acrylamide gel electrophoresis analyses under nonreducing conditions. This 80-kDa species is not metabolically labeled, as is a minor 80-kDa glycoprotein found in the cores, membranes, and an isolated transmembrane complex with actin. Antibodies prepared against the 80-kDa glycoprotein react strongly with bovine IgM and more weakly with rat IgM. These antibodies were used to demonstrate that the 80-kDa component is present in microvilli, microvillar microfilament cores, and microvillar membranes only if the microvilli are prepared in the presence of calf serum. The 80-kDa component, purified by velocity sedimentation in dodecyl sulfate, reacts with anti-rat IgM by immunoblot analyses. Moreover, immunoprecipitation of detergent extracts of microvilli with anti-rat IgM specifically sediments the 80-kDa component. The 80-kDa glycoprotein fractionates with the actin-containing transmembrane complex prepared by gel filtration of Triton-solubilized microvillar membranes. These results indicate that the disulfide-linked, multi-meric 80-kDa component is bovine IgM, which binds strongly to a cell-surface component of the microvilli, and is indirectly associated with the microfilament cores. Thus, the IgM provides a marker by which the transmembrane complexes to the microfilaments can be identified.

Molecular tools for inactivating a yeast enzyme in vivo

As part of an effort to develop a new means of inducibly inactivating cellular proteins in vivo, three monoclonal antibodies which neutralize yeast alcohol dehydrogenase (ADH) activity were isolated and characterized with respect to criteria important for the inactivation strategy. The significance of these criteria is considered, and a general means of generating appropriate antibodies is suggested. All three antibodies described here were specific for ADH I; they did not recognize the closely related isozyme ADH II in a plate-binding assay and did not immunoprecipitate molecules other than ADH from a Saccharomyces cerevisiae extract. Neutralization occurred in a yeast extract and, for two antibodies, was blocked by high concentrations of the coenzyme NAD+. This finding suggests that the antibodies may block enzyme activity by stabilizing an inactive form of ADH lacking bound NAD+. These results provide a foundation for the use of these antibodies to inactivate ADH in vivo.

Molecular tools for inactivating a yeast enzyme in vivo

As part of an effort to develop a new means of inducibly inactivating cellular proteins in vivo, three monoclonal antibodies which neutralize yeast alcohol dehydrogenase (ADH) activity were isolated and characterized with respect to criteria important for the inactivation strategy. The significance of these criteria is considered, and a general means of generating appropriate antibodies is suggested. All three antibodies described here were specific for ADH I; they did not recognize the closely related isozyme ADH II in a plate-binding assay and did not immunoprecipitate molecules other than ADH from a Saccharomyces cerevisiae extract. Neutralization occurred in a yeast extract and, for two antibodies, was blocked by high concentrations of the coenzyme NAD+. This finding suggests that the antibodies may block enzyme activity by stabilizing an inactive form of ADH lacking bound NAD+. These results provide a foundation for the use of these antibodies to inactivate ADH in vivo.

Identification of secretory immunoglobulin A in human sweat and sweat glands

Secretory immunoglobulin A (sIgA) plays an important role in local immune defense mechanisms. Although skin is always exposed to external antigens, the role of local immune defenses involving sIgA in the skin has not been adequately studied. In order to evaluate the presence of sIgA in sweat, we have measured the concentration of sIgA in human sweat by enzyme immunoassay and have localized the components of sIgA in the sweat glands of human axillary skin. The concentration of sIgA in sweat was found to be 10 times higher in men than in women (13.0 +/- 0.9 micrograms/ml versus 1.6 +/- 0.9 micrograms/ml). Secretory component (SC) was localized immunohistochemically in protein synthetic organelles, such as the perinuclear spaces and Golgi complex, in cytoplasmic vesicles, and along the external surface membranes of mucous cells on the terminal segment of eccrine sweat glands. IgA and J chain were present in plasma cells in the protein synthetic organelles. The luminal aspects of eccrine sweat ducts also strongly express SC, as well as IgA and J chain. Neither SC, IgA, or J chain were identified in epithelial cells of apocrine sweat glands. These findings are consistent with the theory that J chain complexed with dimeric IgA is synthesized in plasma cells and is transported by SC-mediated endocytosis transfer across mucous cells of eccrine sweat glands and thus into sweat.

The control of membrane and secreted heavy chain biosynthesis varies in different immunoglobulin isotypes produced by a monoclonal B cell lymphoma

The control of production of the membrane (m) vs secreted (s) forms of immunoglobulin heavy chains was investigated in a panel of cell lines expressing different heavy chain classes but identical light chains (lambda) and variable regions. These cell lines could be induced towards Ig secretion by mitogen treatment. During this process a shift from m to s heavy chain production takes place. Here we show that, similarly to IgA- and IgE-producing B cells, in IgG2a-producing I.29 cells the gamma m-gamma s shift was accompanied by a shift in the corresponding mRNAs, with a decrease of gamma m mRNA and an increase of the gamma s mRNA in LPS-stimulated cells. By contrast, the micron mRNA was increased in LPS-stimulated IgM-producing cells, albeit these cells synthesized reduced amounts of micron polypeptides. The utilization of the translational level in the early steps of B lymphocyte maturation thus distinguishes the mode of regulation of mu chains from those of the other isotypes. In addition, in B cells a post-translational event blocks the secretion of IgM but not of IgG or IgE.

Precursor B cells transformed by Epstein-Barr virus undergo sterile plasma-cell differentiation: J-chain expression without immunoglobulin

Human bone marrow cells were depleted of B lymphocytes to enrich for precursor B cells that could be transformed with Epstein-Barr virus. Transformed immunoglobulin-negative precursors either maintained their immunoglobulin genes in the germ-line configuration or had undergone DJ or abortive VDJ rearrangements (V, D, and J represent variable, diversity, and joining gene segments). All cell lines and their derivative clones, even those with no detectable immunoglobulin gene rearrangements, generated subpopulations of cells that produced high levels of joining (J) chain when analyzed by immunoprecipitation after biosynthetic labeling and by blot hybridization of cytoplasmic RNA. Morphologic and immunofluorescence analyses revealed that J-chain production was confined to clonal progeny that had exited the cell cycle to undergo plasma-cell differentiation. Analysis of cell surface antigens revealed expression of several B-cell maturational markers, including complement receptor type 2 (CR2) and plasma cell antigen 1 (PCA-1). Epstein-Barr virus can thus transform B-cell progenitors, allowing them to proliferate and undergo terminal B-cell differentiation coupled with J-chain expression. These events appear to occur independently of the immunoglobulin gene status of the transformed cells.

Binding of immunoglobulins to the major progesterone-induced proteins secreted by the sheep uterus

We examined the binding of immunoglobulins to the uterine milk proteins, the major progesterone-induced proteins secreted by uterine endometrium of pregnant ewes. Binding was ascertained by measuring binding of 125 I-immunoglobulin to uterine milk proteins that were Western or dot-blotted to nitrocellulose or were coupled to Sepharose. The magnitude of binding was greatest for sheep IgM, intermediate for sheep secretory IgA, low for human secretory and serum IgA, and barely detectable for sheep IgG. Binding of IgA and IgM to uterine milk proteins was time and concentration dependent, saturable, inhibited by high ionic strength buffers, and lost due to enzymatic destruction of the Fc portion of the immunoglobulin molecule. In conclusion, the uterine milk proteins preferentially bind IgA and IgM in a species-dependent manner. Such binding may be related to the role of these proteins in the uterus and may make the uterine milk proteins a useful tool for studying or purifying sheep immunoglobulins.

Recent studies of the interaction of rabbit dimeric IgA with its polymeric immunoglobulin receptor

Rabbit secretory components (SC) constitute a highly heterogeneous population of glycoprotein molecules that are present in secretions as free or bound forms to polymeric immunoglobulins (Ig). Two SC families are known, one of high molecular weight (approximately equal to 80 Kd) composed of five (perhaps six) domains related to Ig variable domains, and one of low molecular weight (approximately equal to 55 Kd). An account of our most recent experimental data is reviewed in this article. We have shown: 1) that both the high and low Mr SC families possess the same relative avidity for binding to dimeric IgA of the g-subclass; 2) that the first NH2-terminal domain of SC derived from the high and low Mr polypeptides is necessary and sufficient for efficient non-covalent binding to dimeric IgA of the g-subclass; 3) that the low Mr SC polypeptide derives from the high Mr SC by the internal deletion of the entire second and third domains, suggesting that these domains are not involved in the binding reaction with polymeric Ig; 4) that the heterogeneity of rabbit secretory components is, in large part, due to the expression of several polymorphic forms (allotypes) susceptible to be recognized by specific alloantisera; the biochemical characterization of the three known SC allotypes (t61, t62 and t63) reveals that t62 and t63 are structurally very similar to each other and markedly divergent from the t61 homologue; 5) that by using non-cross-reactive alloantisera, the major immunodominant allotopes are confined within the COOH-terminal domains 3, 4 and 5 of SC; 6) that the location of the residues involved in the attachment of the carbohydrate unit within domain 1 varies according to the allotype: t61 is N-linked glycosylated at position 70, whereas about 75% of t62 molecules are devoid of sugars; the remaining 25% of t62 molecules are glycosylated at residue position 90; these oligosaccharide chain units are linked to asparagine residues in the acceptor site consensus sequence, Asn-X-Thr/Ser; 7) that the presence of the carbohydrate unit in domain 1 is not required for efficient binding of this domain to polymeric Ig: indeed, after enzymatic deglycosylation, domain 1 exhibits a relative binding avidity which is indistinguishable from that of the native glycosylated domain 1.

Epstein-Barr virus-transformed human precursor B cell lines: altered growth phenotype of lines with germ-line or rearranged but nonexpressed heavy chain genes

A series of lymphoblastoid cell lines (LCLs) have been established by in vitro infection of fetal bone marrow and fetal liver cells with Epstein-Barr virus (EBV). While most lines showed the usual mature B cell phenotype, a small proportion were cytoplasmic and surface immunoglobulin (Ig) heavy and light chain negative. Analysis of gene rearrangements indicated that the Ig- lines were either germ-line or nonproductively rearranged when probed for JH and were in germ-line configuration for C chi; no mu or chi mRNA could be detected in such cells. Precursor B cell lines were indistinguishable from their normal Ig+ counterparts in their expression of a wide variety of cell surface markers including "activation" antigens usually associated with the lymphoblastoid state; even the single LCL showing germ-line heavy and light chain genes expressed B lineage-specific cell surface antigens. However, the Ig- lines were distinct from their Ig+ counterparts in three important respects: (a) they grew much more slowly and achieved lower saturation densities, (b) they showed unusually high proportions (8-16%) of cells in EBV-productive cycle, and (c) they contained unusually high proportions (up to 40%) of cells expressing free joining (J) chain. These results suggest that precursor B cells differ in their response to the growth-transforming effects of EBV such that the virus-cell interaction in precursor B cell lines is inherently less stable than in conventional LCL. In particular there may be a greater movement of cells out of cycle and along the B cell maturation pathway. It is possible that such movement leads in individual cells either to virus replication or to a "sterile" plasmacytoid differentiation with J chain expression in the absence of Ig synthesis.

Nucleolus-associated J chains in myeloma cells: clinical significance

Bone marrow aspirates from 20 patients with multiple myeloma (MM), 4 with smoldering multiple myeloma (S-MM), 1 with idiopathic Bence Jones proteinuria (I-BJP), and 6 with primary macroglobulinemia (PMG) were examined for nucleolus-associated J chain. The incidence of nucleolar J chain-positive (J+) cells among nucleolated cells producing M-component was measured. This incidence (94.0-100%) in terminal MM was significantly higher than that (0-58.0%) in non-terminal MM. Judging from a low incidence in the remission phase, chemotherapy might cause a selective elimination of less differentiated myeloma cells with J+ nucleoli and might have some effect on J chain synthesis. The incidence of nucleolar J+ cells was very low in S-MM. The IgM cells in PMG, where J chain is present in a disulfide-linked form, had no or few J+ nucleoli. No correlation between the incidence of nucleolar J+ cells among nucleolated plasma cells and the percentage of nucleolated cells or that of J+ cells was found. Large J+ nucleoli seemed to be another morphological feature indicating anaplastic myeloma cells. A high incidence of nucleolar J+ cells may be one of the indicators for progressive disease.

Immunoglobulin J chain gene from the mouse

During a primary immune response, murine B lymphocytes are induced to express the gene for the immunoglobulin J chain. As a first step in determining the mechanism of induction, genomic DNA clones encoding the murine J chain were obtained from cell lines representative of B lymphocytes before and after J chain expression. Analysis of the coding regions showed that the J chain gene has a different structure from the other immunoglobulin genes. It consists of four exons organized in a simple 7.3-kilobase transcription unit that does not require DNA rearrangement or alternative processing for expression. These structural properties indicate that transcription of the J chain gene is initiated by changes in chromatin conformation, probably involving a J chain-specific DNA-binding factor. Analysis of the 5' flanking sequences of the J chain gene, on the other hand, showed that the promoter region contains two conserved elements that have been implicated in the lymphocyte-specific expression of the light chain genes. The sharing of these elements suggests that, once the J chain gene is activated, its transcription is regulated by mechanisms similar to those controlling the light chain genes.

Secretory component as the mucosal transport receptor: separation of physicochemically analogous human IgA fractions with different receptor-binding capacities

This paper describes the separation and characterization of several IgA fractions from the same human monoclonal source, based on their ability to bind secretory component (SC). The study was undertaken to elucidate features of the immunoglobulin-binding site for SC, and to examine the dependence of mucosal transport on IgA-SC interaction. Enrichment or depletion of SC-binding activity was accomplished on an affinity adsorbant made with SC from human colostral whey. The affinity-purified human IgA fractions contained IgA polymers and were 77% active in rebinding to the adsorbant; this activity was diminished significantly by direct radioiodination. The non-adherent IgA fractions contained both polymer and monomer, and were only 8% active in rebinding to the adsorbant. When the polymer and monomer components were separated from each other, the non-adherent polymer was found to resemble the affinity-purified fraction by all criteria examined including J-chain content, except that the SC-binding capacity was greater than five-fold lower. These findings have two implications for the SC-binding site on human IgA: first, the presence of J-chain is insufficient to bestow IgA with SC-binding activity; second, a critical tyrosine participates in maintaining the SC-binding region, possibly on the IgA heavy chain. The relationship between SC binding and mucosal transport was tested in the rat hepatobiliary model. All radiolabeled human IgA fractions were captured rapidly from blood by the rat liver, but only the SC-binding fractions underwent substantial intact transport to bile (greater than 70% of the injected dose). Even though a nominal proportion of the SC-non-adherent IgA appeared in bile (4-15% of the dose), most IgA in these fractions was rapidly degraded within the liver. Thus, only a small amount of monomeric and polymeric IgA can use alternative receptors to get to bile by diversion from the degradative pathway. Polymeric IgA can undergo efficient transport across the cell, strictly conditional on a high binding capacity for SC. This demonstrates that membrane SC is the receptor conferring specificity on the mucosal-transport pathway.

Truncated mu (mu') chains in murine IgM. Evidence that mu' chains lack variable regions

Secreted IgM was shown to contain truncated mu (mu') chains with an apparent molecular mass of approximately 55 kD. The estimated percentage of IgM heavy (H) chains in the mu' form ranged from less than or equal to 1% in the case of one tumor IgM protein (104E) to greater than or equal to 30% in normal serum IgM. Serum mu' chains lacked antigenic determinants characteristic of immunoglobulin variable regions and showed a restricted isoelectric focusing pattern compared with that of conventional mu chains. Intracellular mu' chains were readily detected in bone marrow cells but not in spleen or lymph node cells; mu' chains were also detected in IgM-producing tumor cells and in a hybridoma cell line that deleted its productive mu allele. These results predict irregularities in IgM structure and recall an old controversy concerning the valence of IgM molecules.

Secretory component: the polymeric immunoglobulin receptor. What's in it for the gastroenterologist and hepatologist?

The primary function of the SC-pIg system is to secrete pIgs into various external secretions. The cellular mechanism responsible for this transport is schematically depicted in Figure 5. Polymeric immunoglobulin A, which is synthesized by plasma cells that are part of the mucosa-associated lymphoid tissue, gains access to the SC on the abluminal surface of epithelial cells by diffusion from sites of synthesis in mucosae or enters the blood circulation and is cleared, largely by hepatic transport, into bile. The pIgA binds to SC on the abluminal surface of the epithelial cells (and probably hepatocytes) initially by noncovalent interactions that are saturable, reversible, and specific for pIgA and IgM. Subsequently, covalent interaction between SC and its ligand occurs to a variable degree in different species. The SC-IgA complex is endocytosed by the epithelial cell or hepatocyte and is transported across the cell into the external secretions by a microtubule-dependent vesicular transport mechanism. At some point during the transport, the complex is rendered soluble by proteolytic cleavage of the membrane-associated SC molecule to release the soluble sIgA into the gland lumen or the canaliculus. In the intestinal lumen, SC helps protect the sIgA molecule from proteolytic degradation. The sIgA may play a major role in the mucosal defense against pathogenic organisms or harmful antigens. The SC-pIg system differs from many of the other known receptor-ligand interactions in several important ways. First, the synthesis or expression of the receptor (SC), or both, are not regulated by the concentration of the ligand. Second, SC probably is not dissociated from its ligand or recycled to the cell surface as it is secreted in complex with its ligand (pIg) into the external secretions. Third, the interaction of pIgs with their receptor does not function to regulate an intracellular process, but results in transcellular transport of the ligand, which acts in the external environment. Fourth, after initial noncovalent, reversible binding between the receptor and its ligand, the interaction becomes covalent by the formation of disulfide linkages between SC and the pIg. Finally, SC is initially inserted into the abluminal domain of epithelial cells as an integral membrane protein and subsequently is proteolytically cleaved to a soluble molecule which is secreted by the cell. Thus, in contrast to many cell-surface receptor-ligand interactions in which the ligand is ultimately degraded and the receptor is conserved, the SC-pIgA interaction results in partial proteolytic degradation of the receptor and conservation of the ligand.(ABSTRACT TRUNCATED AT 400 WORDS)

J-chain expression in human cells producing IgG subclasses

Previous studies have demonstrated that J chain is expressed not only in cells that produce polymeric immunoglobulins, but also in those engaged in synthesis of monomers including IgG and IgD. The presence of J chain in these cells suggested that its role may not be restricted to the formation of polymers. For the present study, fluorochrome-labeled polyclonal anti-J-chain and monoclonal antibodies to IgG subclasses were used to determine the distribution of J chain in IgG plasma cells from normal human tissues and from pokeweed mitogen (PWM)-stimulated human peripheral blood lymphocytes. The results indicate that J chain is not equally distributed among cells producing different IgG subclasses. The percentages of PWM-stimulated cells containing J chain were: 22 +/- 5 (SE) for IgG1, 49 +/- 6 for IgG2, 17 +/- 7 for IgG3, and 64 +/- 11 for IgG4. Examination of sections of various human lymphoid tissues revealed that the frequency of IgG cells that coexpressed J chain was lower than that observed in the PWM system and displayed variable distribution among IgG subclasses. The frequency of J-chain expression in IgG-producing cells may be related to the degree of cellular maturation and may differ according to the origin of cells.

Dermatitis herpetiformis: biochemical properties of the granular deposits of IgA in papillary dermis. Characterization of SDS-soluble IgA-like material and potentially antigen-binding IgA fragments released by pepsin

Granular deposits of IgA in radioactively labeled thin slices of papillary dermis from 4-mm punch biopsies of clinically normal skin from patients with dermatitis herpetiformis were solubilized with sodium dodecyl sulfate (SDS) or peptic digestion at pH 4.5. Solubilized IgA-like material was isolated by immunoprecipitation and analyzed by electrophoresis in one and two dimensions in polyacrylamide gels containing SDS followed by autoradiography. SDS extracts contained IgA-like components corresponding to monomers, dimers, as well as higher polymers of IgA. A fraction of the SDS-soluble material behaved like IgA upon immunoprecipitation but could not be deaggregated to alpha- and light chains by reduction and alkylation, suggesting that it was present as irreversible aggregates with itself or with other proteins. Peptic digestion at pH 4.5 released fragments which were precipitated by antibodies to human alpha-chains and had molecular weights similar to the proteolytic fragments corresponding to F(ab)2 and Fab formed by peptic digestion of human monomeric IgA under the same conditions.

IgA nephropathy--accumulated experience and current concepts

Primary IgA nephropathy is the most common form of glomerulonephritis in Australia. The condition presents in a variety of ways, but commonly with synpharyngitic hematuria, most often in young men in the third and fourth decades. The course of the disease is indolent but there is progression to renal failure in up to one quarter of cases. Renal biopsy morphology is variable but the essential immunofluorescence finding is diffuse mesangial IgA staining of greater intensity but often in association with other immunoglobulins. C3 is usually also present. Mesangial cellularity is increased in some two-thirds of cases, one third being of a minor focal or variable extent and one-third diffuse. Focal segmental lesions, hyaline nodules and vascular changes are frequent. Crescents are also often present. The etiology of the disease is uncertain but has been linked with HLA antigens, elevated serum IgA levels, IgA polymers, immune complexes and impaired T cell function. Secondary forms of mesangial IgA deposition occur with mucosal defects, hyperglobulinemia or impaired hepatobiliary clearance, and these may offer some insight into the immunopathogenesis of the primary disease.

Human J chain gene. Structure and expression in B lymphoid cells

As part of an ongoing investigation of the regulation of gene expression in B cell development, we have obtained a genomic DNA clone encoding the human J chain protein. The nucleotide sequence of exons encoding the mature protein defines a 137 amino acid primary sequence similar to that previously determined at the protein level. Probes from the gene have been used to analyze J chain expression in human cell lines corresponding to pre-B and B lymphocytes. J chain RNA was detected in two of six human pre-B cell lines and in 8 of 10 B cell lines expressing various Ig isotypes. The expression of the J chain gene is, thus, not tightly linked to IgM or IgA secretion. Our data do not, however, support the recent suggestion (7) that synthesis of J chain precedes that of mu chain in B lymphocyte differentiation. Because of the presence of nine candidate polyadenylation signals (AATAAA or AATTAAA) downstream of the C-terminal coding block of the J chain gene, the 3' end of the gene could not be determined from sequence data alone. To define the 3' end, J chain RNA from a human B lymphocyte line was used to protect an end-labelled DNA fragment from S1 nuclease digestion. The sequence 40 basepairs 5' of the functional polyadenylation site identified by these S1 experiments is homologous the same region of a previously reported mouse J chain complementary DNA clone.

Expression of an X-linked gene family (XLR) in late-stage B cells and its alteration by the xid mutation

One of the most extensively studied X-linked immunodeficiency disorder is the xid mutation of the mouse strain CBA/N. This mutation may involve a maturational defect as xid animals are unable to raise antibodies to soluble polysaccharide antigens, a function normally attributed to late-stage B cells. Moreover, studies using monoclonal antibodies have defined a B-cell surface antigen (BLA-2 or 14G8) that is expressed on most or all immature B lymphocytes, but not on a subpopulation of mature splenic B lymphocytes; this late-stage, 14G8 antigen-negative splenic B-cell subpopulation is apparently absent from mice bearing the xid defect. In the accompanying paper we describe the isolation of a cDNA clone recognizing a family of genes on the X chromosome, at least some of whose members are closely linked to the xid trait. We report here that this gene family, XLR, is transcribed in certain B- and T-cell lineage tumours, but not in macrophage tumours, or liver or kidney cells. We show that it is transcribed principally in late-stage, 14G8-negative B-cell tumours and plasmacytomas, but not in immature B-cell or pre-B-cell tumours. We are able to detect transcription in all of 12 plasmacytomas (secretory B-cell tumours) derived from mice with normal X chromosomes, but not in three plasmacytomas carrying the xid mutation. These data, combined with the restriction fragment length polymorphism analysis linking the XLR gene family to the xid mutation, suggests that the xid defect occurs within a member of this gene family.

Mechanism of neutralization of influenza virus by secretory IgA is different from that of monomeric IgA or IgG

We have found that bile is a useful source of secretory IgA (scIgA) which can specifically neutralize influenza virus infectivity. Using purified scIgA, we compared the mechanism of neutralization with that mediated by IgA monomers (prepared from scIgA by differential reduction) and IgG. At 4 degrees C, scIgA prevented the attachment of neutralized virus, while neither monomeric IgA nor IgG had any affect on this process or on the subsequent stages of infection by which virion RNA accumulates in nuclei. At 25 and 37 degrees C, scIgA permitted the attachment of approximately half the neutralized virus, but the virus was not internalized. Clearly, the neutralization depends on the character of the antibody used. scIgA may act by steric hindrance (with attachment or penetration, depending on temperature), whereas IgA and IgG neutralize infectivity at a stage subsequent to accumulation of the virus genome in the nucleus.

Ontogeny of J chain expression in pig lymphocytes

The ontogeny of lymphocytes expressing J chain in the cytoplasm (J+) was studied in pig foetuses by the immunofluorescent technique. Peripheral blood lymphocytes were the first J+ cells in prenatal life. The spleen and lymph nodes contained J+ cells in the last days of gestation. J+ cells were found in the lamina propria of the gut and some glands of conventional but not of germ-free piglets. J chain was not detected on or in cell membranes at any developmental stage.

An immunocytochemical study on secretory mechanism of IgA in human pancreas

To analyze the secretory mechanism of immunoglobulins into pancreatic secretion, pancreatic juice IgA was measured by single radial immunodiffusion and characterized immunochemically, and immunoglobulins, J chain and secretory component (SC) were localized immunocytochemically in pancreatic tissues by the peroxidase-labeled antibody method. The concentration of IgA was 0.0225 mg/ml with a range of 0.010 to 0.049. IgA associated with SC was demonstrated immunochemically in three cases. IgA, SC and J chain were demonstrated immunocytochemically in the pancreatic duct epithelium with the features characteristic of endocytic, SC-mediated transfer of IgA. The results of the present study suggested that transfer of IgA linked by J chain and SC across ductal epithelial cells, but not acinar cells occurred in human pancreas.

The pleated sheet: an unusual negative-staining method for transmission electron microscopy of biological macromolecules

A novel method for preparing negatively stained specimens is described which appears to improve the routine resolution of biological structure in direct images obtained by transmission electron microscopy. In the new method, which we term the pleated sheet technique, macromolecules are adsorbed to a carbon film by the Valentine procedure (R. Valentine, B. Shapiro, and E. Stadtman (1968) Biochemistry, 7, 2143-2152), and the film then carefully pleated while in contact with a 1% uranyl formate solution to trap stain within the folds of pleats. A grid is placed on the compressed film, and film plus grid retrieved with a Saran Wrap drum. Subsequent dehydration produces a filmed grid containing negatively stained macromolecules within the folds of pleated regions and positively stained macromolecules in single sheet regions. The effect of sandwiching sample and stain between carbon layers is to produce exceedingly uniform negative staining so that stain contours more accurately and more reproducibly reflect true molecular contours. Electron micrographs of IgG and IgA molecules prepared by these methods are exhibited that permit unambiguous comparison of structure imaged in the electron microscope against known structures solved by single-crystal X-ray diffraction. Correlation is excellent; the smallest resolvable element in micrographs is an immunoglobulin domain, whose molecular weight is 12 000.

Changes in J chain and mu chain RNA expression as a function of B cell differentiation

The time course of differentiative events in the pentamer IgM response was examined by following the expression of J chain and mu chain RNA and their protein products in mitogen-stimulated lymphocytes. The analyses showed that the shift to mus RNA synthesis begins shortly after stimulation and precedes proliferation of the cells and any increase in mu RNA levels. In contrast, expression of J chain RNA and the amplification of J chain and mus message are late events that coincide with a phase of rapid proliferation and with the secretion of pentamer IgM antibody. The kinetics of J and mu chain RNA expression observed in normal lymphocytes were supported by analyses of lymphoid cell lines. B lymphomas were found to display the RNA pattern characteristic of early-activated lymphocytes, i.e., a partial shift to mus RNA production and no J chain RNA, whereas IgM-secreting lines resembled late-activated lymphocytes in their expression of high levels of both mus and J chain mRNA. Moreover, the kinetics of J and mus chain RNA expression correlates with the sequential action of B cell lymphokines in the induction of the pentamer IgM response. This correlation suggests that the successive differentiative changes are triggered by successive membrane stimuli.