Immunofunctional properties of a yolk sac epithelial cell line expressing two proteins gp280 and gp330 of the intermicrovillar area of proximal tubule cells: inhibition of endocytosis by the specific antibodies

The apical domain of epithelial cells lining the proximal tubule and the yolk sac is characterized by the development of extensive microvilli which limit intermicrovillar spaces backed on their cytoplasmic aspect by a coat of clathrin. These membrane areas which give rise to endocytic vesicles are characterized by the expression on their outer aspect of two high molecular weight glycoproteins: gp330 and gp280. In this study we report on an epithelial cell line, BN/MSV, derived from a yolk sac carcinoma which expresses these two glycoproteins. By indirect immunofluorescence, gp330 and gp280 were detectable on the cell surface and after permeabilization in intracytoplasmic vesicles. At the ultrastructural level they were concentrated in clathrin-coated membrane areas and although gp280 could also be detected in non-coated areas. The two proteins were synthesized independently in the form of high molecular weight polymers by biosynthetically labeled BN/MSV cells. Both were released in the supernatant, but, in spite of previously reported similarities by peptide mapping, only gp330 coprecipitated with a 45 kDa protein comigrating with the alpha 2-macroglobulin receptor-associated protein (MRAP). Culture of the cells in the presence of antibodies to gp280 and to a lesser extent of antibodies to gp330 inhibited the internalization of [14C]sucrose and peroxidase. When followed intracellularly at the ultrastructural level, the compartments containing peroxidase in the presence of anti-gp280 or gp330 antibodies were morphologically distinct from those observed under control conditions: vesicles were of smaller size and irregular shape and accumulation in lysosomes was delayed.(ABSTRACT TRUNCATED AT 250 WORDS)

Heavy endosomes isolated from the rat renal cortex show attributes of intermicrovillar clefts

The endosomal pathway of the rat renal cortex was labeled by intravenous infusion of fluorescent dextran small enough to cross the glomerular ultrafiltration barrier and be taken up by luminal endocytosis. A fraction containing entrapped fluorescein was isolated from a cortical homogenate after differential centrifugation and Percoll density gradient centrifugation. This fraction has been dubbed heavy endosomes. To our surprise, small-particle flow cytometry techniques demonstrated that heavy endosomes are homogeneous for entrapped fluorescein dextran and the presence of H(+)-adenosinetriphosphatase activity. The abundance of heavy endosomes, combined with the findings that true endosomal populations are identifiable in other renal cortical fractions, led us to test whether heavy endosomes had the attributes of intermicrovillar clefts. First, we tested whether heavy endosomes vesiculate in vivo or in vitro. Vesicle-by-vesicle flow cytometry analysis of uptake of fluorescein dextran added to the homogenate demonstrated that virtually all the vesicles form in vitro (99 +/- 2%, n = 4). Second, the fraction contains markers associated with intermicrovillar clefts: clathrin light chains, actin, glycoprotein gp280, and gp330, the "Heymann antigen." The presence of the brush border enzyme markers gamma-glutamyl transpeptidase and leucine aminopeptidase in > 99% of the heavy endosomes confirms that the vesicles are of apical origin. The activity of the enzymes colocalized with entrapped markers but was tenfold less than in brush-border membrane vesicles. Heavy endosomes isolated from the rat renal cortex vesiculate in vitro and contain several intermicrovillar markers.

Heterogeneity of endosomal populations in the rat renal cortex: light endosomes

The endosomal pathway of the rat renal cortex was labeled by intravenous infusion of fluorescent dextran small enough to cross the glomerular ultrafiltration barrier and be taken up by luminal endocytosis in the proximal tubule. Using Percoll gradient centrifugation, we isolated and characterized a previously undetected renal cortical endosomal fraction slightly lighter than basolateral membranes. Assay of entrapped dextran on a vesicle-by-vesicle basis using small-particle flow cytometry techniques demonstrates homogeneity for entrapped dextran. Flow cytometry colocalization of entrapped markers with brush-border enzymes in > 99% of the vesicles and the absence of Na-K-adenosinetriphosphatase (ATPase) suggest both that these vesicles are of apical origin and that apical enzymes traffic into endosomal elements. Furthermore, two glycoproteins derived from intermicrovillar clefts are detectable in this fraction. Ultrastructurally the vesicles are heterogeneous, consisting of multivesicular bodies together with vesicles of diverse size and coating. Populations of vesicles can be cleanly separated from each other and basolateral membranes according to their surface charge by high-resolution free-flow electrophoresis. Multiparameter flow cytometry analysis demonstrates that a more abundant population of smaller vesicles has brisker H(+)-ATPase activity, whereas a less abundant population of larger vesicles has slower H(+)-ATPase activity. In contrast, brush-border membrane vesicles contained no entrapped markers and lacked H(+)-ATPase activity. Analysis of vesicles prepared after addition of dextran to the homogenate confirms that the vesicles form in vivo. Hence a heterogeneous renal cortical endosomal population is of apical origin.

Trafficking of apical proteins into clathrin-coated vesicles isolated from rat renal cortex

The endosomal pathway of the rat renal cortex was labeled by intravenous infusion of fluorescent dextran small enough to cross the glomerular ultrafiltration barrier and be taken up by luminal endocytosis in the proximal tubule. Clathrin-coated vesicles (CCV) were isolated from the rat renal cortex utilizing discontinuous sucrose density gradients and negative lectin selection. More than 99 +/- 1% (n = 4) of the isolated vesicles contain entrapped fluorescein dextran when analyzed by small-particle flow cytometry techniques. Similarly, flow cytometry analysis demonstrates brisk H(+)-adenosinetriphosphatase activity in virtually all the vesicles. Western blot analysis of the vesicle proteins with a polyclonal anticlathrin antibody stains bands consistent with clathrin and adaptins. When the isolated vesicles are decoated by exposure to 0.5 M tris(hydroxymethyl)aminomethane, the proteins released match the molecular weights of the proteins identified on Western blot analysis. Flow cytometry demonstration of brush border enzymes in > 99% of the vesicles and Western blot identification of maltase suggests both that these vesicles are of apical origin and that apical enzymes traffic into endosomal elements. Additionally, two glycoproteins detectable in this fraction on Western blot analysis and flow cytometry immunocytochemistry are derived from intermicrovillar clefts traffic into the endosomal pathway. Hence, apical proteins traffic into a population of CCV isolated from the rat renal cortex.

Immunological reactivity of angiotensin II receptor antagonists: possible implications for receptor binding sites

In the present study, we assessed the reactivity with seven anti-angiotensin II monoclonal antibodies of three nonpeptide and one peptide compounds described as selective antagonists of angiotensin II for AT1 (DuP 753, 2-n-butyl-4-chloro-5-(hydroxymethyl)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl] methyl] imidazole; EXP 3174, 2-n-butyl-4-chloro-5-(carboxylic acid)-1-[[2'-(1H-tetrazol-5-yl) biphenyl-4-yl] methyl] imidazole) and AT2 receptor sites (CGP42112A, nicotinyl-Tyr-(N alpha-benzyloxycarbonyl-Arg)Lys-His-Pro-Ile-OH; PD123177, 1-[(4-amino-3-methylphenyl) methyl]-5-(diphenyl-acetyl)-4,5,6,7-tetrahydro-1H-imidazol[4,5-c] pyridine 6-carboxylic acid), respectively. These studies were undertaken because the reactivity of the monoclonal antibodies with peptide analogs of angiotensin II and the three-dimensional structure of an angiotensin II-immunoglobulin Fab fragment complex strongly suggested that the conformations identified by the monoclonal antibodies were relevant to those involved in receptor binding as defined by biophysical models supported by structure activity studies. Surprisingly although three of the compounds were described as competitive inhibitors of angiotensin II, binding of the various monoclonal antibodies to either ovalbumin-coupled angiotensin II adsorbed to plastic wells or 125I-labeled angiotensin II in liquid phase was unaffected by any of the nonpeptide antagonists and CGP42112A up to 10(-4) M concentration. The antagonists also failed to bind to rabbit polyclonal anti-angiotensin II antibodies. Direct binding experiments in which solid phase-immobilized angiotensin II and DuP 753 conjugates were incubated with anti-angiotensin II or anti-DuP 753 monoclonal antibodies, did not show any cross-reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Major influence of cell differentiation status on characteristics of proteoglycans synthesized by cultured rabbit renal proximal tubule cells: role of insulin and dexamethasone

To analyze the influence of epithelial cell differentiation and the effects of hormones on the characteristics of cell-associated and secreted proteoglycans (PGs), we studied their distribution, synthesis, and biochemical features in a model of renal proximal tubule cells in primary culture in which cell differentiation could be controlled by medium composition. In cells cultured in serum-free, hormonally defined medium supplemented with insulin and dexamethasone that exhibited a high degree of morphological and functional proximal differentiation (Ronco et al., 1990), cell-associated PGs were similar to those extracted in vivo by their size estimated by Sepharose CL-6B chromatography (Kav = 0.27, vs. 0.26), composition (heparan-sulfate), and localization in a continuous basal layer of extra-cellular matrix (ECM). In contrast, major quantitative and qualitative anomalies of cell-associated PGs were observed in poorly differentiated cells grown in 1% fetal calf serum-supplemented medium (FCS). PGs alterations included: (1) reduced and irregular expression of PGs at the cell basal pole, (2) a 2.8-fold decrease in [35S]-sulfate incorporation into cell-associated PGs, (3) a 3.1-fold increase in trypsin-releasable PGs, and (4) the emergence of a high MW PG composed exclusively of chondroitin-sulfate (CS) (Kav = 0.09 on Sepharose CL-6B) as well as of putative free CS-glycosaminoglycan (GAG) chains (Kav = 0.49 on Sepharose CL-6B). The same alterations were identified in the basal defined medium devoid of hormones but were partially or totally abolished by addition of insulin and dexamethasone, respectively. At variance with cell-associated PGs, production and biochemical features of secreted PGs were not influenced by cell differentiation status and medium composition.

Dramatic changes of sulfated proteoglycans composition in a tumorigenic SV-40-transformed renal proximal-tubule cell line

To characterize the sulfated proteoglycans (PGs) alterations associated with malignant transformation of epithelial cells in vitro, the localization, charge, size, and composition of cell-associated and secreted sulfated PGs have been compared in rabbit renal proximal-tubule cells in primary culture (Ronco et al., 1990) and in a derived SV-40 transformed cell line (RC.SV1) exhibiting a proximal phenotype and high tumor-inducing ability (Vandewalle et al., 1989). Both normal and transformed cells incorporated PGs into a thick basement membrane layer as shown by ruthenium red staining and immunodetection with a monoclonal antibody raised against the core protein of the bovine basement membrane heparan sulfate-PG (HS-PG). In primary cultures of normal cells, cell-associated PGs were almost identical to those extracted from renal tubule fractions in vivo by their size (Kav = 0.27 vs. 0.26 on Sepharose CL-6B) and composition characterized by the exclusive presence of heparan sulfate glycosaminoglycan (HS-GAG) chains. In addition, the cells secreted a HS-PG with similar biochemical characteristics (Kav = 0.29; 100% HS-GAG chains). The SV-40-transformed RC.SV1 cells also synthesized and secreted a unique PG with the same charge and Kav values and apparently the same core protein (35 kDa) as in nontransformed cells, but three major differences were observed: (i) an increased proportion of PG-associated [35S]sulfate radioactivity released into the culture medium (36 vs. 21%), (ii) the emergence of free GAG chains unincorporated into PGs and detected only in the cell-associated fraction, and (iii) a dramatic change in the composition of GAG chains in which chondroitin sulfate replaced heparan-sulfate. The latter finding is in keeping with the known chondroitin sulfate increase and heparan-sulfate decrease in epithelial tumors. The alterations of PGs observed in this study may play a role in the acquisition and/or maintenance of the malignant phenotype.

Three-dimensional structure of an angiotensin II-Fab complex at 3 A: hormone recognition by an anti-idiotypic antibody

The elucidation of bioactive conformations of small peptide hormones remains an elusive goal to structural chemists because of the inherent flexibility of these molecules. Angiotensin II (AII), the major effector of the renin-angiotensin system, is an octapeptide hormone for which no clear structural models exist. Peptide hormones such as AII share the property that they bind to their receptors with high affinities, in spite of the fact that they must overcome an extremely large conformational entropy barrier to bind in one conformation. A "surrogate system" that consists of a high-affinity monoclonal antibody (MAb) and AII has been used to study a bound conformation of AII. The crystallographic structure of the complex reveals a structure of AII that is compatible with predicted bioactive conformations of AII derived from structure-activity studies and theoretical calculations. In the complex, the deeply bound hormone is folded into a compact structure in which two turns bring the amino and carboxyl termini close together. The antibody of this complex (MAb 131) has the unusual property that it was not generated against AII, but rather against an anti-idiotypic antibody reactive with a MAb to AII, which renders this antibody an anti-anti-idiotypic antibody. The high affinity for AII of the original MAb to AII was passed on to MAb 131 through a structural determinant on the anti-idiotypic antibody. Strikingly, the conformation of AII in this complex is highly similar to complementarity determining region loops of antibodies, possibly indicating that a true molecular mimic of bound AII was present on the anti-idiotypic antibody against which MAb 131 was elicited.

Recognition of angiotensin II: antibodies at different levels of an idiotypic network are superimposable

Genetic and sequence information are reported for an angiotensin II-reactive antibody (Ab1, MAb 110) and an anti--anti-idiotypic antibody (Ab3, MAb 131) that have identical antigen binding properties and that are related by an anti-idiotypic antibody (Ab2-beta) that satisfies accepted biochemical criteria for an internal image-bearing antibody. The sequences of the variable regions of the Ab3 and of the Ab1 are nearly identical, even though the Ab1 is an antibody to a peptide and the Ab3 is an antibody to a globular protein. Significantly, amino acid residues that make critical contacts with antigen in the crystal structure of the Ab3-antigen complex are highly conserved in Ab1, suggesting that the epitopes of the Ab2-beta recognized by the Ab3 do indeed resemble the bound structure of the antigen.

Antagonist effect of a receptor-mimicking peptide encoded by human angiotensin II complementary RNA

This article reports on the binding and the angiotensin II (Ang II) antagonistic properties of a peptide, referred to as hIIA, encoded by an RNA strand complementary to the human Ang II messenger RNA. Although Ang II and hIIA (H2N-Glu-Gly-Val-Tyr-Val-His-Pro-Val-COOH) share four amino acids, the iodinated and tritiated forms of hIIA were unreactive with seven monoclonal antibodies defining four distinct epitopes on the Ang II molecule and failed to bind to Ang II hepatic and mesangial receptors. However, hIIA did inhibit binding of 125I-Ang II to rat hepatocyte membranes (IC50, 2 x 10(-7) M) and to the various monoclonal antibodies. The lowest IC50 (5 x 10(-7) M) was measured with the monoclonal antibody specific for the Ang II sequence generally considered as implicated in receptor recognition. As predicted from the binding studies, hIIA was further shown to antagonize some biological properties of Ang II. On mesangial cells, hIIA alone had no effect on intracellular calcium concentration ([Ca2+]i) and prostaglandin E2 synthesis but did abolish the transient increase in [Ca2+]i in response to 100 nM Ang II and did induce a specific dose-dependent inhibition of the Ang II-stimulated prostaglandin E2 release. Furthermore, intravenous infusion of hIIA (200 micrograms.kg-1.min-1) inhibited by 66 +/- 3% the rat hypertensive response to 100 ng.kg-1 Ang II but had no effect on the pressor activity of agents such as alpha 1-adrenergic and HT2 serotonin agonists. Our data suggest that the "complementary" peptide hIIA interacts directly with Ang II by mimicking the Ang II complementary site on the receptor and can inhibit the physiological effects of Ang II. This type of Ang II complementary peptide may serve as a model for a new class of antihypertensive drugs.

Activation of the simian virus 40 (SV40) genome abrogates sensitivity to AVP in a rabbit collecting tubule cell line by repressing membrane expression of AVP receptors

To analyze the role of SV40 genome in the phenotypic alterations previously observed in SV40-transformed cell lines, we infected rabbit renal cortical cells with a temperature-sensitive SV40 mutant strain (tsA58) and compared the cell phenotypes at temperatures permissive (33 degrees C) and restrictive (39.5 degrees C) for SV40 genome expression. At both temperatures, the resulting cell line (RC.SVtsA58) expresses cytokeratin and uvomorulin, but epithelial differentiation is more elaborate at 39.5 degrees C as shown by the formation of a well-organized cuboidal monolayer with numerous tight junctions and desmosomes. Functional characteristics are also markedly influenced by the culture temperature: cells grown at 33 degrees C respond only to isoproterenol (ISO, 10(-6) M) by a sevenfold increase in cAMP cell content above basal values; in contrast, when transferred to 39.5 degrees C, they exhibit increased sensitivity to ISO (ISO/basal: 19.1) and a dramatic response to 10(-7) M dDarginine vasopressin (dDAVP/basal: 18.2, apparent Ka: 5 X 10(-9) M) which peaks 48 h after the temperature shift. The latter is associated with membrane expression of V2-type AVP receptors (approximately 50 fmol/10(6) cells) which are undetectable when SV40 genome is activated (33 degrees C). Clonal analysis, additivity studies, and desensitization experiments argue for the presence of a single cell type responsive to both AVP and ISO. The characteristics of the RC. SVtsA58 cell line at 39.5 degrees C (effector-stimulated cAMP profile, lack of expression of brush-border hydrolases and Tamm-Horsfall protein) suggest that it originates from the cortical collecting tubule, and probably from principal cells.

Angiotensin II (AII)-related idiotypic network. III. Comparative analysis of idiotopes and paratopes borne by monoclonal antibodies raised against AII (AB1) and its internal image (AB3)

We have previously produced mAb against angiotensin II (AII), a phylogenetically conserved vasopressive octapeptide, and shown that they identify four distinct epitopes on the AII molecule. In addition we used internal image bearing polyclonal antiidiotypic antibodies raised against rabbit anti AII to produce mAb3. In this study we analyze the segregation of the idiotypic and paratopic repertoires of the mAb1 and mAb3. Analysis of mAb1 carried out with polyclonal Ab2 raised against the four distinct paratopes permitted classification of the mAb1 into four categories: (p+, id+) comprises antibodies with shared paratopic and idiotypic specificities: (p+, id-) is made up of antibodies that fail to express the Id defined by Ab2 raised against other antibodies pertaining to the same paratopic group; (p-, id+) includes antibodies that express cross-reactive Id on distinct paratopes; (p-, id-) refers to antibodies unrelated by their paratopes and Id mAb2 confirmed these results and showed expression of identical or closely related Id on clearly distinct paratopes. At the Ab3 level, using polyclonal Ab4, there was a higher degree of Id cross-reactivity between the two paratopes available. These data suggest that the parallel set concept may apply to the immune response to a natural peptidic Ag and its internal image. Comparison of idiotypic repertoires of mAb1 and mAb3 (using Ab2 and Ab4 antibodies) confirmed the lack of public Id and showed the predominance on mAb3 of "new" idiotypes absent from mAb1 molecules, as expected for internal image-induced antibodies. Cross-reactive idiotypes defined on mAb1 and conserved on mAb3 were expressed on the two paratopes defined at the Ab3 level. They were located on the H chain of the homologous paratope and required the association of H and L chains on the heterologous paratope. Our analysis suggests that, in the AII system, the idiotypic and paratopic repertoires segregate at least in part independently. The paratopic repertoire is limited to a small number of phylogenetically conserved specificities and may be encoded by germline genes. In contrast, the idiotypic repertoire is broader with respect to specificities, species, and localization on H and L chains. This extended diversity may be generated by somatic mutations or use of various combinations of H and L chains and/or V, D, J segments.

Angiotensin II (AII)-related idiotypic network. III. Comparative analysis of idiotopes and paratopes borne by monoclonal antibodies raised against AII (AB1) and its internal image (AB3)

We have previously produced mAb against angiotensin II (AII), a phylogenetically conserved vasopressive octapeptide, and shown that they identify four distinct epitopes on the AII molecule. In addition we used internal image bearing polyclonal antiidiotypic antibodies raised against rabbit anti AII to produce mAb3. In this study we analyze the segregation of the idiotypic and paratopic repertoires of the mAb1 and mAb3. Analysis of mAb1 carried out with polyclonal Ab2 raised against the four distinct paratopes permitted classification of the mAb1 into four categories: (p+, id+) comprises antibodies with shared paratopic and idiotypic specificities: (p+, id-) is made up of antibodies that fail to express the Id defined by Ab2 raised against other antibodies pertaining to the same paratopic group; (p-, id+) includes antibodies that express cross-reactive Id on distinct paratopes; (p-, id-) refers to antibodies unrelated by their paratopes and Id mAb2 confirmed these results and showed expression of identical or closely related Id on clearly distinct paratopes. At the Ab3 level, using polyclonal Ab4, there was a higher degree of Id cross-reactivity between the two paratopes available. These data suggest that the parallel set concept may apply to the immune response to a natural peptidic Ag and its internal image. Comparison of idiotypic repertoires of mAb1 and mAb3 (using Ab2 and Ab4 antibodies) confirmed the lack of public Id and showed the predominance on mAb3 of "new" idiotypes absent from mAb1 molecules, as expected for internal image-induced antibodies. Cross-reactive idiotypes defined on mAb1 and conserved on mAb3 were expressed on the two paratopes defined at the Ab3 level. They were located on the H chain of the homologous paratope and required the association of H and L chains on the heterologous paratope. Our analysis suggests that, in the AII system, the idiotypic and paratopic repertoires segregate at least in part independently. The paratopic repertoire is limited to a small number of phylogenetically conserved specificities and may be encoded by germline genes. In contrast, the idiotypic repertoire is broader with respect to specificities, species, and localization on H and L chains. This extended diversity may be generated by somatic mutations or use of various combinations of H and L chains and/or V, D, J segments.

Crystallization and preliminary X-ray diffraction data of an anti-angiotensin II Fab and of the peptide-Fab complex

mAb-131 is a monoclonal antibody that binds with high affinity (K alpha = 7.4 x 10(9) M-1) to the 8-residue peptide hormone angiotensin II, the major effector of the renin/angiotensin system. mAb-131 is a member of a well characterized idiotypic antibody network since it was raised as an anti-anti-idiotype of an antibody raised against angiotensin II. mAb-131 Fabs prepared with papain contain four major charge isoforms that can be separated by pH gradient elution from an anion-exchange column. Diffraction quality isomorphous crystals of two of the isoforms and of the Fab.peptide complexes have been grown. The crystals diffract to 3.5 A resolution, are tetragonal, space group P4(1) (or P4(3] with cell dimensions a = b = 78.6 A, c = 125.2 A, and have two Fab molecules per asymmetric unit. By using a different buffer, a second crystal form has been grown which diffracts to 3.3 A. It also belongs to space group P4(1) (or P4(3] but has cell dimensions of a = b = 109.6 A and c = 125.2 A. Knowledge of the three-dimensional structure of this Fab and of the peptide.Fab complex will give insight into two problems: 1) the recognition of small peptide hormones (which exist as random coils in solution) with high affinity by proteins, and 2) the nature of conservation of antibody combining sites in idiotypic networks.

Angiotensin II (AII)-related idiotypic network. II. Heterogeneity and fine specificity of AII internal images analyzed with monoclonal antibodies

Although the structural basis of internal images borne by beta type monoclonal anti-idiotypic antibody (Ab2) begins to be elucidated, there is little information on the repertoire of epitopes which make up the internal images expressed by polyclonal Ab2. We addressed this question by using a two-way approach in the angiotensin II (AII)-related idiotypic network, a system characterized by common occurrence of internal images on rabbit Ab2. First, two sets of internal images were purified in parallel by affinity chromatography on Sepharose 4B covalently linked to either mAb 110 (S4B-110), a mAb specific for a phenylalanine requiring carboxy terminus epitope (Phe8) on AII, or mAb 133 (S4B-133), reactive with a more central epitope also expressed on Phe8 substituted peptide analogs. The respective eluates, EL1 110 and E11 133, exhibited only partially overlapping reactivity, as demonstrated by 1) a different pattern of inhibition by various AII peptide analogues of EL1 110 and E11 133 binding to the same anti-AII antibody (Ab1) (either the homologous polyclonal Ab1 102 or mAb 133), 2) and a distinct profile of EL1 110 and EL1 133 binding to 12 biotinylated monoclonal Ab1 identifying a variety of epitopes on AII. To analyze further the respective distribution of mAb 110 and mAb 133 defined epitopes on Ab2-beta molecules, Ab2 were submitted to sequential affinity chromatography on S4B-110 followed by S4B-133, and the fractionated internal images were characterized by the pattern of binding to the various monoclonal Ab1. It was thus possible to purify two Ab2-beta subpopulations that exclusively imaged the determinant identified by mAb 110 (ii 110) or that identified by mAb 133 (ii 133). A third subpopulation which was successively retained on S4B-110 and S4B-133 expressed both internal images (ii 110 + 133), and was additionally reactive with all the other monoclonal Ab1 tested. In any case, monoclonal Ab1 binding to the different sets of internal images was totally inhibited by an excess of AII. These results indicate that the repertoire of internal epitopes is similar to that of the nominal Ag, but is scattered over distinct subpopulations of Ab2-beta molecules that can be fractionated by affinity chromatography. Some of the latter seem to bear several epitopes and resemble the whole nominal Ag, whereas others appear to image only one determinant. Second, we raised 7 anti-anti-idiotypic mAb (monoclonal Ab3) against affinity-purified Ab2-beta and analyzed their fine specificity for AII.(ABSTRACT TRUNCATED AT 400 WORDS)

Angiotensin II (AII)-related idiotypic network. I. Common occurrence of AII internal image on rabbit anti-idiotypic antibodies

Internal images of foreign Ag have been demonstrated in a variety of systems as anticipated by the idiotypic network theory formulated by Jerne. However, they seem to be of rare occurrence. In order to estimate the actual frequency of antibodies bearing internal images (Ab2-beta) of angiotensin II (AII), a phylogenetically conserved peptide made up of eight amino acids, nine rabbits were immunized with affinity or protein A purified anti-AII antibodies (Ab1) from allotype-matched rabbits. Four of nine antiidiotypic antibodies (Ab2) exhibited internal image-like reactivity. They recognized all the polyclonal Ab1 tested, whatever the species (rabbit, mouse, guinea pig). In addition, they were strongly reactive with three mAb specific for a carboxy terminus epitope on AII (mAb 110, 199, and 211) and with a fourth monoclonal Ab1 (133) identifying a more central epitope. Advantage was taken of this reactivity with mAb1 to purify Ab2-beta by affinity chromatography of Ab2 on Sepharose 4B covalently linked to the three monoclonal Ab1 specific for the carboxy terminus epitope. The eluate displayed typical internal image properties: 1) it reacted with all the polyclonal Ab1 tested, 2) this reaction was completely abolished by AII, and 3) rabbits and mice immunized with the eluate all produced Ab1. The AII related idiotypic network is thus characterized by high frequency and immunogenicity of AII internal images. In addition, reactivity of the latter with monoclonal Ab1 indicates variable expression on Ab2-beta of the epitopes defined by the mAb on the nominal Ag.

Angiotensin II (AII)-related idiotypic network. I. Common occurrence of AII internal image on rabbit anti-idiotypic antibodies

Internal images of foreign Ag have been demonstrated in a variety of systems as anticipated by the idiotypic network theory formulated by Jerne. However, they seem to be of rare occurrence. In order to estimate the actual frequency of antibodies bearing internal images (Ab2-beta) of angiotensin II (AII), a phylogenetically conserved peptide made up of eight amino acids, nine rabbits were immunized with affinity or protein A purified anti-AII antibodies (Ab1) from allotype-matched rabbits. Four of nine antiidiotypic antibodies (Ab2) exhibited internal image-like reactivity. They recognized all the polyclonal Ab1 tested, whatever the species (rabbit, mouse, guinea pig). In addition, they were strongly reactive with three mAb specific for a carboxy terminus epitope on AII (mAb 110, 199, and 211) and with a fourth monoclonal Ab1 (133) identifying a more central epitope. Advantage was taken of this reactivity with mAb1 to purify Ab2-beta by affinity chromatography of Ab2 on Sepharose 4B covalently linked to the three monoclonal Ab1 specific for the carboxy terminus epitope. The eluate displayed typical internal image properties: 1) it reacted with all the polyclonal Ab1 tested, 2) this reaction was completely abolished by AII, and 3) rabbits and mice immunized with the eluate all produced Ab1. The AII related idiotypic network is thus characterized by high frequency and immunogenicity of AII internal images. In addition, reactivity of the latter with monoclonal Ab1 indicates variable expression on Ab2-beta of the epitopes defined by the mAb on the nominal Ag.

Angiotensin II (AII)-related idiotypic network. II. Heterogeneity and fine specificity of AII internal images analyzed with monoclonal antibodies

Although the structural basis of internal images borne by beta type monoclonal anti-idiotypic antibody (Ab2) begins to be elucidated, there is little information on the repertoire of epitopes which make up the internal images expressed by polyclonal Ab2. We addressed this question by using a two-way approach in the angiotensin II (AII)-related idiotypic network, a system characterized by common occurrence of internal images on rabbit Ab2. First, two sets of internal images were purified in parallel by affinity chromatography on Sepharose 4B covalently linked to either mAb 110 (S4B-110), a mAb specific for a phenylalanine requiring carboxy terminus epitope (Phe8) on AII, or mAb 133 (S4B-133), reactive with a more central epitope also expressed on Phe8 substituted peptide analogs. The respective eluates, EL1 110 and E11 133, exhibited only partially overlapping reactivity, as demonstrated by 1) a different pattern of inhibition by various AII peptide analogues of EL1 110 and E11 133 binding to the same anti-AII antibody (Ab1) (either the homologous polyclonal Ab1 102 or mAb 133), 2) and a distinct profile of EL1 110 and EL1 133 binding to 12 biotinylated monoclonal Ab1 identifying a variety of epitopes on AII. To analyze further the respective distribution of mAb 110 and mAb 133 defined epitopes on Ab2-beta molecules, Ab2 were submitted to sequential affinity chromatography on S4B-110 followed by S4B-133, and the fractionated internal images were characterized by the pattern of binding to the various monoclonal Ab1. It was thus possible to purify two Ab2-beta subpopulations that exclusively imaged the determinant identified by mAb 110 (ii 110) or that identified by mAb 133 (ii 133). A third subpopulation which was successively retained on S4B-110 and S4B-133 expressed both internal images (ii 110 + 133), and was additionally reactive with all the other monoclonal Ab1 tested. In any case, monoclonal Ab1 binding to the different sets of internal images was totally inhibited by an excess of AII. These results indicate that the repertoire of internal epitopes is similar to that of the nominal Ag, but is scattered over distinct subpopulations of Ab2-beta molecules that can be fractionated by affinity chromatography. Some of the latter seem to bear several epitopes and resemble the whole nominal Ag, whereas others appear to image only one determinant. Second, we raised 7 anti-anti-idiotypic mAb (monoclonal Ab3) against affinity-purified Ab2-beta and analyzed their fine specificity for AII.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of monoclonal antibodies specific for human Tamm-Horsfall protein

Fifteen monoclonal antibodies have been produced to human Tamm-Horsfall protein (THP), identifying at least seven distinct epitopes. The antibodies have been used to isolate from serum an immunoreactive protein which comigrates with urinary THP. In addition, the antibodies may prove useful to set up an immunoenzymoassay for urinary THP as well as for immunoaffinity purification.

A new form of familial glomerulonephritis

An unusual familial glomerular disease, characterized by the presence of diffuse round mesangial deposits of C3, is described in 2 siblings (1 male and 1 female) and their mother. The clinical picture in the 3 patients was a long-lasting proteinuria. An acute hemolytic uremic syndrome with malignant hypertension developed in the male at the age of 24 years, requiring bilateral nephrectomy. The glomerulonephritis recurred on a renal allograft. This disease is not HLA-linked and no characteristic abnormality of complement profile was seen in the 3 patients.

The detection of circulating immune complexes in renal transplant patients

The Raji cell assay and radiolabelled Clq binding method were used to detect circulating immune complexes in the sera of renal transplant patients. Complexes were found in seven of twelve patients using the Raji cell assay; only one serum sample was positive by the Clq method. In five patients the complexes were detected prior to the clinical diagnosis of rejection and in those in whom treatment reversed the rejection the complexes rapidly disappeared. The presence of complexes correlated with a vascular type of rejection characterised by fibrin deposits in the glomeruli in the absence of immunoglobulin or C3 deposits. In two patients, in whom anti red cell antibodies were present, irreversible rejection occurred without the presence of detectable complexes in the sera.

Circulating immune complexes and C3d in human parasitosis

Using the Raji cell radioimmune assay, we found low levels of circulating immune complexes (IC) in a small percentage of patients with schistosomiasis and filariasis. C3d levels, measured by immunoprecipitation, were elevated in a large number of these patients, whereas complement levels were within normal limits. Proteinuria was not found in any of the 55 patients studied. Circulating IC or elevated C3d levels were not found in any of the 19 patients with hydatidosis. The increased C3d levels, apparently not related to circulating IC, may be due to direct complement activation by parasite antigens or to sequestered IC. The latter hypothesis appears more attractive because the highest levels of C3d were found in schistosomiasis whereas schistosome antigens were unable to activate complement in vitro.

A study of the material inhibiting EAC-rosette formation in the sera of patients with nephropathies

Significant levels of EAC-rosette inhibition compared to control subjects were found in the sera of patients with focal and segmental hyalinosis (FSH), membranoproliferative glomerulonephritis (MPGN) and extra-membranous glomerulonephritis (EGN). In patients with IgA disease, although some sera produced high levels of inhibition, the group as a whole did not differ significantly from the controls. Evidence was obtained suggesting that the rosette inhibitory activity was due to immune complexes (IC) bearing C3 rather than C3 fragments. Firstly, the inhibitory activity was precipitable by 4% PEG, a concentration which does not precipitate the C3 fragments. Secondly, the inhibitory activity was selectively removed from the PEG precipitates by an anti-human immunoglobulin G immunoabsorbent. Finally, since it had been suggested that in some instances an unknown serum factor could inhibit EAC-rosette formation and activation of the alternative pathway of complement, the latter was studied and found to be normal in all the sera studied. Taken together, these results suggest that the inhibition of EAC-rosette formation obtained with the sera of the patients studied was due to the presence in these sera of some material behaving as IC. No clear-cut association was, however, seen between rosette inhibition and the presence or absence of Ig or C3 deposits in the kidney.