A homing receptor-IgG chimera as a probe for adhesive ligands of lymph node high endothelial venules

The binding of lymphocytes to high endothelial venules (HEV) within peripheral lymph nodes (pln) is thought to be mediated by a lectinlike adhesion molecule termed the pln homing receptor (pln HR). The cloning and sequencing of cDNAs encoding both murine and human pln HR revealed that these adhesion molecules contain protein motifs that are homologous to C-type or calcium dependent lectin domains as well as to epidermal growth factor (egf) and complement-regulatory protein domains. We have produced a novel, antibody-like form of the murine HR by joining the extracellular region of the receptor to a human IgG heavy chain. This antibody-like molecule is capable of recognizing carbohydrates, blocking the binding of lymphocytes to pln HEV, and serving as a histochemical reagent for the staining of pln HEV. This murine HR-IgG chimera should prove useful in analyzing the distribution of the HR ligand(s) in normal as well as in inflammatory states.     

Cell membrane IgD: demonstration of IgD on human lymphocytes by enzyme-catalyzed iodination and comparison with cell surface Ig of mouse, guinea pig, and rabbit.

A substantial fraction of human cord blood and peripheral blood lymphocytes have recently been shown to bear IgD. Although IgD has not been identified in mice, it has been suggested that it is also a major surface immunoglobulin of murine lymphocytes. Thus, lactoperoxidase-catalyzed iodination of surface immunoglobulin of mouse spleen and lymph node cells reveals the existence of an IgH chain differing from mu, gamma, and alpha-chain both antigenically and by mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This new H chain class has been previously proposed to be the mouse homologue of delta-chain. In this paper, we analyzed human, mouse, guinea pig, and rabbit lymphoid cell membrane Ig by lactoperoxidase-catalyzed iodination, extraction with non-ionic detergent precipitation with a variety of specific anti-Ig sera, and electrophoresis of dissolved reduced precipitates on sodium dodecyl sulfate-polyacrylamide gels. Our studies confirm the previous reports of a new mouse cell membrane H chain with a mobility more rapid than that of mu-chain. However, we fail to detect a molecule with this electrophoretic mobility on the surface of guinea pig or rabbit lymph node and spleen cells. Moreover, neither anti-kappa nor anti-delta antibody precipitates a molecule with an H chain of this mobility from labeled extracts of human cord blood or peripheral blood lymphocytes. Cell surface delta was identified on both human cord blood and peripheral blood lymphocytes, but it proved to have mobility similar to human and mouse mu-chain. This result indicates either that mouse delta-chain has an electrophoretic mobility on sodium dodecyl sulfate-polyacrylamide gels which differs appreciably from that of human membrane delta-chain or that the newly described mouse H chain is not the homologue of human delta-chain.     

Expression of an unidentified immunoglobulin isotype on rabbit Ig-bearing lymphocytes.

A non-IgM immunoglobulin molecule was found on most rabbit Ig-bearing lymphocytes isolated from mesenteric lymph nodes. Membrane bound immunoglobulin light chains and heavy chains were detected by immunofluorescence and by rosetting with antibody-coated erythrocytes on mesenteric lymph node cells stripped of IgM by anti-IgM allotype antibodies. The percentage of cells bearing these residual immunoglobulin molecules was similar to the percentage of cells bearing immunoglobulin before "stripping" with anti-IgM antibody. These residual immunoglobulin molecules were not IgA nor IgG and are believed to be the rabbit analogue of human IgD.     

Genetic and antigenic characterization of fragments of the pheasant immunoglobulin Y heavy chain constant region

Few studies have attempted to characterize the pheasant (Phasianus colchicus) immunoglobulin Y (IgY) heavy chain constant region. In the present study, fragments of the pheasant IgY heavy chain constant region were cloned, analyzed, and expressed. The cross-reactivity of IgY or immunoglobulin G (IgG)s with antigens from other vertebrate species was determined using dot-enzyme-linked immunosorbent assay and western blot analysis. Five peptides of the pheasant IgY heavy chain constant region were synthesized to determine its immunoregulatory activity in vitro. The IgY heavy chain constant region from pheasant showed the highest homology with that from chicken (71.2 %) and duck (49.1 %). Phylogenetic analysis for IgY showed that pheasant was closely related to chicken and duck than to any other analyzed vertebrate species. The rabbit anti-chicken IgG showed immunologic cross-reactivity with recombinant proteins of the pheasant IgY heavy chain constant region. Four peptides were able to induce significant up-regulation of interleukin (IL)-1β, IL-4, and interferon-γ in chicken peripheral blood lymphocytes, suggesting a new role of avian IgY in immune regulation.     

Modulation of human rheumatoid factor-specific lymphocyte responses with a cross-reactive anti-idiotype bearing the internal image of antigen

Rabbit anti-idiotypic antibodies to human rheumatoid factor (RF) autoantibodies were isolated by affinity chromatography on rabbit anti-human IgG Fc Sepharose 4B. The anti-idiotypic antibodies bore the "internal image" of the antigen, human IgG. They reacted specifically with multiple human monoclonal and polyclonal IgM-RF, independent of any particular light or heavy chain amino acid sequence. The anti-idiotypes did not react with IgM or IgG proteins lacking RF activity. The present experiments determined the potential of the "internal image" antibodies to modulate in vitro lymphocyte functions. The addition of anti-idiotypic antibody to peripheral blood mononuclear cell cultures from patients with rheumatoid arthritis elicited lymphocyte proliferation, but not RF synthesis. The antibody did not induce the proliferation of lymphocytes from a normal individual. Moreover, the anti-idiotype specifically suppressed IgM-RF secretory responses when preincubated with B cells before co-culture with autologous pokeweed mitogen-activated T cells. The data show that the anti-idiotypic antibodies with the "internal image" of antigen are capable of interacting with B cell receptors in an antigen-restricted manner, and possess specific immunomodulatory properties.     

The binding of complement component C3 to antibody-antigen aggregates after activation of the alternative pathway in human serum.

Preformed immune aggregates, containing antigen and either IgG (immunoglobulin G) or F(ab')2 rabbit antibody, were incubated with normal human serum under conditions allowing activation of only the alternative pathway of complement. Both the IgG and F(ab')2 immune aggregates bound C3b, the activated form of the complement component C3, in a similar manner, 2-3% of the C3 available in the serum being bound to the aggregates as C3b, and the rest remaining in the fluid phase as inactive C3b or uncleaved C3. It was found that the C3b was probably covalently bound to the IgG in the aggregates, since C3b-IgG complexes could be demonstrated on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, after repeated washing with buffers containing high salt or boiling under denaturing conditions. Incubation of the C3b-antibody-antigen aggregates in buffers known to destroy ester linkages had little effect on the C3b-IgG complexes, which suggested that C3b and IgG might be linked by an amide bond. Two main types of C3b-IgG complexes were found that had apparent mol.wts. of 360000 and 580000, corresponding to either one to two C3b molecules respectively bound to one molecule of antibody. On reduction of the C3b-IgG complexes it was found that the beta-chain, but not the alpha'-chain, of C3b was released along with all the light chain of IgG but only about half or less of the heavy chain of IgG. These results indicate that, during activation of the alternative pathway of complement by immune aggregates containing IgG antibody, the alpha'-chain of C3b may become covalently bound at one or two sites in the Fd portion of the heavy chain of IgG.     

CD5+ B cells predominate in peripheral tissues of rabbit.

Restricted usage of VH genes is observed in rabbit B lymphocytes and in human and murine CD5 B lymphocytes. This observation raised the possibility that most rabbit B lymphocytes were CD5+. To investigate this we cloned the CD5 gene from a rabbit cosmid library, using a probe derived from human CD5 cDNA. The rabbit CD5 gene was transfected into a murine T cell line and then we used the transfectants to develop anti-rabbit CD5 mAb. By Western blot analysis, the mAb reacted with a 67-kDa protein in lysates prepared from mesenteric lymph node and spleen cells. We determined the frequency of CD5+ B lymphocytes in peripheral lymphoid tissues of adult rabbits by two-color immunofluorescence analysis using anti-CD5 mAb and anti-L chain antibodies. The analysis showed that essentially all peripheral B lymphocytes in adult rabbits express CD5. The observation that CD5 is expressed on nearly all rabbit B lymphocytes contrasts markedly to mouse and human, where only a small number of B lymphocytes express CD5. We propose that most peripheral B lymphocytes in rabbit, as in chicken, develop early in ontogeny and are maintained throughout life by a self-renewing process.     

Sequence studies on the heavy chain of rabbit immunoglobulin A of different alpha-locus allotypes.

The amino acid sequence was determined of part of the variable region of heavy chain from rabbit immunoglobulin A of allotypes a1 and a3. Two corrections of the primary sequence of Aa1 gamma-chains are reported; most of the structural correlates of the alpha-locus allotypes are confirmed. The amino acid sequence of the N-terminal 20 residues of alpha-negative molecules was also determined and found to be homologous to the human VhIII subgroup. These molecules are present in a much higher proportion in the alpha-chain pool than in the gamma-chain.     

Fc gamma-receptor-bearing, non-B lymphocytes in human peripheral blood: cytophilic immunoglobulin binds almost exclusively to large granular lymphocytes

Cytophilic IgG (CYT-Ig) has previously been reported to bind to both the "TG" (E+, Fc gamma R+) and "L" (E-, Fc gamma R+) subsets of non-B lymphocytes in human peripheral blood. Present investigations show that IgG-binding cells, as detected by a sensitive antiglobulin rosetting reaction, are contained almost entirely within the large granular lymphocyte (LGL) subpopulation, and that fewer than 5% of other non-B lymphocytes acquire IgG from serum. Cell membrane-bound IgG sterically blocks the reaction of LGL with sheep red blood cells and therefore influences the proportions of these cells characterized as TG (E+) or L (E-) lymphocytes. Although the majority of TG lymphocytes are LGL, a further subpopulation of E+, Fc gamma R+ cells are detectable under particular test conditions. Unlike LGL, these lymphocytes do not react with rabbit IgG-coated ox RBC (EAG) in saline, but will form EAG rosettes when the reaction is enhanced in the presence of Ficoll. These Fc gamma R+ cells are mostly of typical small-lymphocyte morphology and do not bind detectable amounts of CYT-Ig, nor do they express the monoclonal antibody-defined VEP 13 determinant associated with Fc gamma R on LGL.     

Production and Characterization of Monoclonal Antibodies Against Myelin-Associated Glycoprotein

Monoclonal antibodies against myelin-associated glycoprotein were generated by fusing mouse myeloma cells with spleen lymphocytes from BALB/c mice immunized with human myelin-associated glycoprotein purified from CNS myelin. Three groups of antibodies were identified: IgG antibodies recognizing the polypeptide moiety and IgG and IgM antibodies recognizing the carbohydrate moiety of the intact molecule. Properties of these antibodies were examined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and the immunostaining technique using human CNS and peripheral nerve myelin, and ganglioside fractions isolated from human brain and peripheral nerve, and with immunohistochemical staining of human peripheral nerves. Part of human peripheral blood mononuclear cells was stained with the antibodies against the carbohydrate moiety, but not with IgG antibodies recognizing the polypeptide moiety. Natural killer activity was partially reduced after treatment of human peripheral blood lymphocytes with an IgM antibody and complement in vitro. The possibility that anti-myelin-associated glycoprotein antibodies might play a role in the pathogenesis of demyelinating diseases through modification of natural killer activity is discussed.     

Proof of a disulfide bridge accessible to disulfide exchange between the heavy chains of IgG

The paper deals with the direct experimental proof that human immunoglobulin G1 (IgG1) contains a reactive disulfide bond that can be opened by 3,3'-dithiobis(6-nitrobenzoate) (DTNB) within 24 h by a SH-catalysed disulfide exchange reaction. These results were obtained with the purified IgG1 myeloma protein and confirm earlier indirect evidence based on correlation analysis of DTNB reactivity and quantitative IgG1 determination. The reactive disulfide bond is most likely the one between Cys235 of the heavy chains in the "hinge"-region, activated for the disulfide exchange by the protonated amino groups of Lys231 as turned out by analysis of IgG1. As with the whole molecule, one mol of reactive disulfide was found per mol of the Fc-fragment. 0.8 mol of labile S-S bonds was detected per mol of F(ab)2. After separation of the excess of reagent, the sedimentation pattern still corresponded with the dimer. The unaltered antigenic properties as well as the crystallizability speak against any severe conformational changes. Therefrom it was concluded that in approximately 80% of the F(ab)2 molecules one of the two inter heavy chain-bridges was opened. With the isolated F(ab)-fragment a reaction with DTNB was ascertained to an extent of 20%, which is probably due to an altered stability of the heavy-light chain-SS-bridge. However, no influence on the sedimentation pattern was observed. The intrachainar disulfide bonds of neither the heavy nor the light chain reacted with DTNB to a measurable extent.     

Assembly, secretion, and vacuolar delivery of a hybrid immunoglobulin in plants

Secretory immunoglobulin (Ig) A is a decameric Ig composed of four alpha-heavy chains, four light chains, a joining (J) chain, and a secretory component (SC). The heavy and light chains form two tetrameric Ig molecules that are joined by the J chain and associate with the SC. Expression of a secretory monoclonal antibody in tobacco (Nicotiana tabacum) has been described: this molecule (secretory IgA/G [SIgA/G]) was modified by having a hybrid heavy chain sequence consisting of IgG gamma-chain domains linked to constant region domains of an IgA alpha-chain. In tobacco, about 70% of the protein assembles to its final, decameric structure. We show here that SIgA/G assembly and secretion are slow, with only approximately 10% of the newly synthesized molecules being secreted after 24 h and the bulk probably remaining in the endoplasmic reticulum. In addition, a proportion of SIgA/G is delivered to the vacuole as at least partially assembled molecules by a process that is blocked by the membrane traffic inhibitor brefeldin A. Neither the SC nor the J chain are responsible for vacuolar delivery, because IgA/G tetramers have the same fate. The parent IgG tetrameric molecule, containing wild-type gamma-heavy chains, is instead secreted rapidly and efficiently. This strongly suggests that intracellular retention and vacuolar delivery of IgA/G is due to the alpha-domains present in the hybrid alpha/gamma-heavy chains and indicates that the plant secretory system may partially deliver to the vacuole recombinant proteins expected to be secreted.     

Analysis of a cDNA sequence encoding the immunoglobulin heavy chain of the Antarctic teleost Trematomus bernacchii

A spleen cDNA library was constructed from the Antarctic teleost Trematomus bernacchii and immunoscreened with rabbit IgG specific for T. bernacchii Ig heavy chain. Eleven cDNA clones, varying in size and encoding the entire heavy chain or parts of it, were isolated. Here the complete nucleotide and deduced amino acid sequences of clone 2C2 encoding the secretory IgH chain form are reported. Comparison of the amino acid sequence of the entire constant region of the T. bernacchii Ig heavy chain with those from other teleosts and two holostean fish showed percent identity ranging 53.6-60.6%, with the highest values found for Salmoniformes. The multiple sequence alignment revealed the presence of two remarkable insertions: one at the VH-CH1 boundary and a second one, not found in any other IgM heavy chain, localised at the CH2-CH3 boundary. The latter occurred in the region proposed to act as a 'hinge', and resulted in a CH2-CH3 hinge peptide longer than any other IgM hinge. Differences were also found in the number and position of putative N-glycosylation sites of the compared sequences. It is suggested that the unusual features found in the T. bernacchii Ig heavy chain might contribute to the flexibility of the Ig molecule and help understand more about the adaptation of Ig molecules to the polar sea environment.     

MHC class I-related neonatal Fc receptor for IgG is functionally expressed in monocytes, intestinal macrophages, and dendritic cells

The neonatal Fc receptor (FcRn) for IgG, an MHC class I-related molecule, functions to transport IgG across polarized epithelial cells and protect IgG from degradation. However, little is known about whether FcRn is functionally expressed in immune cells. We show here that FcRn mRNA was identifiable in human monocytes, macrophages, and dendritic cells. FcRn heavy chain was detectable as a 45-kDa protein in monocytic U937 and THP-1 cells and in purified human intestinal macrophages, peripheral blood monocytes, and dendritic cells by Western blot analysis. FcRn colocalized in vivo with macrosialin (CD68) and Ncl-Macro, two macrophage markers, in the lamina propria of human small intestine. The heavy chain of FcRn was associated with the beta(2)-microglobulin (beta(2)m) light chain in U937 and THP-1 cells. FcRn bound human IgG at pH 6.0, but not at pH 7.5. This binding could be inhibited by human IgG Fc, but not Fab. FcRn could be detected on the cell surface of activated, but not resting, THP-1 cells. Furthermore, FcRn was uniformly present intracellularly in all blood monocytes and intestinal macrophages. FcRn was detectable on the cell surface of a significant fraction of monocytes at lower levels and on a small subset of tissue macrophages that expressed high levels of FcRn on the cell surface. These data show that FcRn is functionally expressed and its cellular distribution is regulated in monocytes, macrophages, and dendritic cells, suggesting that it may confer novel IgG binding functions upon these cell types relative to typical Fc gamma Rs: Fc gamma RI, Fc gamma RII, and Fc gamma RIII.     

Purine nucleoside phosphorylase in lymphocytes of various mammalian species

Synopsis The distribution of purine nucleoside phosphorylase has been assessed by light and electron microscopy in peripheral lymphocytes of man, the rabbit, rat, mouse, guinea-pig, pig and dog. The enzyme activity was detected in the cytosol of the majority of lymphocytes in all species. The amount of reaction product was high in the rabbit, man, guinea-pig and dog, moderate in the rat and very low in the pig and mouse. Other blood cell types are reactive as well, although there is a variation between species. A possible relationship of purine nucleoside phosphorylase with particular subpopulations of lymphocytes is suggested.     

The mechanism of activation of rabbit plasminogen by urokinase.

The data presented in this paper show that when rabbit plasminogen is activated to plasmin by urokinase at least two peptide bonds are cleaved in the process. Urokinase first cleaves an internal peptide bond in plasminogen, leading to two-chain disulfide-linked plasmin molecule. The plasmin heavy chain of molecular weight 66,000 to 69,000 possesses an NH2-terminal amino acid sequence identical with the original plasminogen (molecular weight 88,000 to 92,000). The plasmin light chain of molecular weight 24,000 to 26,000 is known to be derived from the COOH-terminal portion of plasminogen. The plasmin generated during the activation of plasminogen is capable, by a feedback process, of cleaving a peptide of molecular weight 6,000 to 8,000 from the NH2 terminus of the heavy chain, producing a proteolytically modified heavy chain of molecular weight 58,000 to 62,000. Plasmin also can cleave this same peptide from the original plasminogen, yielding an altered plasminogen of molecular weight 82,000 to 86,000. This plasmin-altered plasminogen and the plasmin heavy chain derived from it by urokinase activation process NH2-terminal amino acid sequences which are identical with each other and with the plasminolytic product of the original plasmin heavy chain. These studies support a mechanism of activation of plasminogen by urokinase which involves loss of a peptide located on the NH2 terminus of plasminogen. However, these same results show that this NH2-terminal peptide need not be released from rabbit plasminogen prior to the cleavage of the internal peptide bond which leads to the two-chain plasmin molecule. Furthermore, these studies show that urokinase cannot remove this peptide from either the original rabbit plasminogen molecule or from the heavy chain of the initial plasmin formed.     

Mitogenic effect on human lymphocytes of insolubilized anti-immunoglobulins. I. Specificity of the stimulating agent

The mitogenic response of peripheral blood lymphocytes to various anti-immunoglobulin reagents has been studied by measuring incorporation of a radioactive thymidine into macromolecules. Coupling of anti-F(ab')2 or anti-light chain antibodies to Sepharose beads leads to a 5-fold increase in their mitogenic capacity with 50-fold less antibodies per culture. Pepsin-digested F(ab')2 fragments had a mitogenic capacity similar to intact antibody molecules. Anti-F(ab')2 antibodies purified by immunoabsorbent columns were found to be more effective as mitogen than unpurified antibody fractions. Antibodies to kappa- or lambda-light chains were found to be mitogenic, whereas antibodies specific to various heavy chain classes failed to induce a significant response. Isolated light chains were much more effective in inhibiting the reaction than isolated mu-chains. It is concluded that insolubilized anti-light chain antibodies are mitogenic to human peripheral blood lymphocytes.     

Reactions of normal human and rabbit immunoglobulins with heart valve fibroblasts]

It was demonstrated using the indirect immunofluorescent technique that normal human and rabbit sera, and IgG isolated from them intensively reacted with fibroblasts of human and bovine heart valves. The results obtained with Fab and Fc fragments of IgG sugges that this reaction is due to the Fc region of the IgG molecule and related to the presence of the Fc receptor on fibroblasts of heart valves.     

Development of purification processes for fully human bispecific antibodies based upon modification of protein A binding avidity

There is strong interest in the design of bispecific monoclonal antibodies (bsAbs) that can simultaneously bind 2 distinct targets or epitopes to achieve novel mechanisms of action and efficacy. Multiple bispecific formats have been proposed and are currently under development. Regeneron's bispecific technology is based upon a standard fully human IgG antibody in order to minimize immunogenicity and improve the pharmacokinetic profile. A single common light chain and 2 distinct heavy chains combine to form the bispecific molecule. One of the heavy chains contains a chimeric Fc sequence form (called Fc*) that ablates binding to Protein A via the constant region. As a result of co-expression of the 2 heavy chains and the common light chain, 3 products are created, 2 of which are homodimeric for the heavy chains and one that is the desired heterodimeric bispecific product. The Fc* sequence allows selective purification of the FcFc* bispecific product on commercially available affinity columns, due to intermediate binding affinity for Protein A compared to the high avidity FcFc heavy chain homodimer, or the weakly binding Fc*Fc* homodimer. This platform requires the use of Protein A chromatography in both a capture and polishing modality. Several challenges, including variable region Protein A binding, resin selection, selective elution optimization, and impacts upon subsequent non-affinity downstream unit operations, were addressed to create a robust and selective manufacturing process.