Basic principles of Antigen-Antibody Reactions

Point-of-Care Testing for Infectious Diseases Based on Class 2 CRISPR/Cas Technology

The early detection of infectious diseases and microorganisms is critical for effective disease treatment, control, and prevention. Currently, nucleic acid testing and antigen-antibody serum reaction are the two methods most commonly used for the detection of infectious diseases. The former is highly accurate, specific, and sensitive, but it is time-consuming, expensive, and has special technician and instrument requirements. The latter is rapid and economical, but it may not be accurate and sensitive enough. Therefore, it is necessary to develop a quick and on-site diagnostic test for point-of-care testing (POCT) to enable the clinical detection of infectious diseases that is accurate, sensitive, convenient, cheap, and portable. Here, CRISPR/Cas-based detection methods are detailed and discussed in depth. The powerful capacity of these methods will facilitate the development of diagnostic tools for POCT, though they still have some limitations. This review explores and highlights POCT based on the class 2 CRISPR/Cas assay, such as Cas12 and Cas13 proteins, for the detection of infectious diseases. We also provide an outlook on perspectives, multi-application scenarios, clinical applications, and limitations for POCT based on class 2 CRISPR/Cas technology.

A peptide-based anti-Adalimumab antibody assay to monitor immune response to biologics treatment in juvenile idiopathic arthritis and childhood chronic non-infectious uveitis

Immune response to biologics treatment, while widely reported, yet fails to correlate with clinical outcomes and assay to assay comparison is often not possible. Hence, we developed a new peptide based-detection assay to stratify pediatric patients with juvenile idiopathic arthritis (JIA) or chronic non-infectious uveitis (CNU) and monitor anti-drug antibodies (ADAbs) formed as part of an immune response to treatment with the fully human monoclonal therapeutic antibody Adalimumab. Adalimumab derived synthetic peptides were optimized for maximum immunogenicity and were tested by SP-ELISA on a development cohort of 18 JIA and CNU treated patients. The two best performing peptides able to differentiate patient groups were selected for evaluation with a larger scale ELISA testing on a total of 29 sera from pediatric patients with JIA or CNU. The results of this peptide-based assay were compared to an in-house developed SPR biosensor ADAbs assay and a commercially available bridging ELISA. The first peptide, termed HC3, was able to positively detect ADAbs in 7 out of the 29 sera, while the second peptide, called LC3, was able to detect ADAbs in 11 out of 29 sera in the evaluation group. Following statistical data evaluation, it has been found that the detection of ADAbs using the peptide-based ELISA assay positively correlates with disease progression and remission. Two synthetic peptides derived from Adalimumab may provide a beneficial tool to clinicians for monitoring patient response to such treatment and taking informed decisions for treatment alternatives.

Sialic acids in the brain: gangliosides and polysialic acid in nervous system development, stability, disease, and regeneration

Every cell in nature carries a rich surface coat of glycans, its glycocalyx, which constitutes the cell's interface with its environment. In eukaryotes, the glycocalyx is composed of glycolipids, glycoproteins, and proteoglycans, the compositions of which vary among different tissues and cell types. Many of the linear and branched glycans on cell surface glycoproteins and glycolipids of vertebrates are terminated with sialic acids, nine-carbon sugars with a carboxylic acid, a glycerol side-chain, and an N-acyl group that, along with their display at the outmost end of cell surface glycans, provide for varied molecular interactions. Among their functions, sialic acids regulate cell-cell interactions, modulate the activities of their glycoprotein and glycolipid scaffolds as well as other cell surface molecules, and are receptors for pathogens and toxins. In the brain, two families of sialoglycans are of particular interest: gangliosides and polysialic acid. Gangliosides, sialylated glycosphingolipids, are the most abundant sialoglycans of nerve cells. Mouse genetic studies and human disorders of ganglioside metabolism implicate gangliosides in axon-myelin interactions, axon stability, axon regeneration, and the modulation of nerve cell excitability. Polysialic acid is a unique homopolymer that reaches >90 sialic acid residues attached to select glycoproteins, especially the neural cell adhesion molecule in the brain. Molecular, cellular, and genetic studies implicate polysialic acid in the control of cell-cell and cell-matrix interactions, intermolecular interactions at cell surfaces, and interactions with other molecules in the cellular environment. Polysialic acid is essential for appropriate brain development, and polymorphisms in the human genes responsible for polysialic acid biosynthesis are associated with psychiatric disorders including schizophrenia, autism, and bipolar disorder. Polysialic acid also appears to play a role in adult brain plasticity, including regeneration. Together, vertebrate brain sialoglycans are key regulatory components that contribute to proper development, maintenance, and health of the nervous system.

Identification of structural features involved in binding of alpha-amanitin to a monoclonal antibody

Twenty-four derivatives of the cyclic octapeptide alpha-amanitin were assayed for their affinities to the monoclonal antibody beta A1/1. The derivatives were of natural, semisynthetic, and synthetic origin and had KD values ranging from 2 nM to > 70 microM. In the majority of the derivatives the chemical modifications had no detectable influence on the overall shape of the double-ring peptide. Given this condition, binding factors could be calculated from KD values of the amatoxin derivatives, which were valid for all amatoxins for estimating the contribution made by single structures to complex formation. The complex between alpha-amanitin and the immunoglobulin involves at least eight sites of contact. Four of them are responsible for strong interactions: (1) the OH group of hydroxyproline2 (binding factor 413), (2) the lipophilic side chain of isoleucine6 (binding factor 131), (3) the -CH2- moiety of the adjacent glycine5 or the absence of a side chain in this position (binding factor 361), and (4) the proton at the indole nitrogen of hydroxytryptophan4 (binding factor 140). The residual four interactions are hydrogen bonds of lower strength corresponding to binding factors of 1.5-8. The key role of the unique conformation of the amatoxins in determining their binding properties was shown by two amatoxin derivatives in which changes in the conformation were associated with virtually complete loss of affinity. For all amatoxin derivatives with conformations similar or identical to that of alpha-amanitin, we found empirical evidence that those structures of the peptide involved in binding make their contributions virtually independent of each other. It is a consequence of this rule that structural features that cooperate in binding could be characterized by the numerical product of their binding factors.

Kinetics of antibody binding at solid-liquid interfaces in flow

We have developed the theoretical framework for a displacement immunoassay conducted in flow under nonequilibrium conditions. Using a repetitive displacement technique, we determined the displacement rate and apparent dissociation rate constant at different flow rates. Our data suggest that the kinetics are best described by a first-order function. The displacement efficiency, the displacement rate, and therefore the apparent dissociation rate constant were calculated and demonstrated to be flow rate dependent. The theoretical framework developed in this study was successful in predicting the behavior of antigen displacement in flow.

Application of immunochemical assays to food analysis

Immunochemical assays are powerful bioanalytical techniques with application to several areas in food science, including food analysis, microbiology, nutrition, food safety, food quality, and process control. In principle, immunochemical techniques can be applied to the analysis of any compound, with only one specific antibody needed that can be obtained either from laboratory animals or, when available, from commercial sources. A well-designed immunochemical assay can detect targeted compounds at levels as low as 10(-12) M. Immunochemical techniques require little or no sample pretreatment, making these analytical procedures relatively rapid. The initial cost of developing an immunoanalytical assay may be high, but when the procedure is well established, the cost per test is often a fraction of that for other analytical methods. For these reasons, immunoanalytical assays provide an attractive alternative for the food analyst who requires either inexpensive qualitative screening tests or reliable quantitative methods with a high degree of sensitivity. This review concentrates on the use of enzyme immunoassay to address analytical problems in food chemistry and the analysis of various food components.

Identity between polysaccharide antigens of Moraxella nonliquefaciens, group B Neisseria meningitidis, and Escherichia coli K1 (non-O acetylated)

A surface polysaccharide antigen of Moraxella nonliquefaciens, reported to be cross-reactive with the capsular polysaccharides of group B Neisseria meningitidis and Escherichia coli K1 (K. Błvre, K. Bryn, O. Closs, N. Hagen, and L. O. Froholm, NIPH Ann. 6:65-73, 1983), was isolated, purified, and characterized chemically, immunologically, and by nuclear magnetic resonance. This polysaccharide was shown to be a linear homopolymer of alpha (2----8)-linked N-acetylneuraminic acid, identical to the capsular polysaccharide of group B N. meningitidis and O-acetyl-negative variants of E. coli K1.

Characterization of a high-affinity monoclonal antibody to calcineurin whose epitope defines a new structural domain of calcineurin A

Monoclonal antibodies have been raised against native calcineurin using conventional in vivo immunization and hybridoma procedures. The relatively high affinity of nonimmune IgG for the two subunits of calcineurin resulted in large nonspecific binding values for immunoassays of native, dissociated and denatured calcineurin, which complicated the antibody screening. Monoclonal aCn5, a high-affinity IgG1 that exhibits specific binding, was characterized. Other calmodulin-binding proteins tested were not recognized by aCn5. Simple binding properties were exhibited in solid-phase experiments, Kd = 26 (+/- 4) pM, but the stoichiometry was low. The loss of immunoreactivity after denaturation of calcineurin indicated that the aCn5 epitope is of the assembled topographic, not segmental, type. The epitope was located to the A subunit and affinity was unaffected by the presence of calcineurin B. The epitope remained intact after proteolytic removal of the amino-terminal 20 residues of calcineurin A essential for phosphatase activity, and the carboxyl-terminal inhibitory and calmodulin-binding domains. The calmodulin-binding peptide derived from calcineurin, cA8, was not recognized by aCn5. Addition of Ca2+, Mn2+, Ni2+, chelators or dithiothreitol did not influence the affinity of aCn5 for the holoenzyme. Phosphatase activity of calcineurin, in the presence and absence of calmodulin and after removal of the inhibitory domain, was little affected by aCn5. Thus, the aCn5 epitope defines a previously unidentified structural domain of calcineurin A located in a region of the proteolytically resistant core that is topologically distinct from the catalytic, inhibitory, calmodulin-binding and calcineurin-B-binding domains, and not functionally connected with calcineurin B or the putative metal-binding domain(s).

A simple method for determination of the concentration of anti-dextran IgG in antiserum by means of affinity electrophoresis

A simple technique for determination of the concentration of anti-dextran IgG in antiserum using affinity electrophoresis is described. In the presence of an excess of intermediary molecular size dextran in the polyacrylamide gel, polyclonal anti-dextran IgG migrated in a single sharp band, separated from the nonspecific IgG fraction and other serum protein fractions. With this technique, 1-10 micrograms anti-dextran IgG in antisera can be determined within 3 h. We call the procedure ligand saturating affinity electrophoresis.

Interaction with a monoclonal antibody alters the expression of co-operativity by phenylalanine hydroxylase from rat liver

Phenylalanine hydroxylase purified from rat liver shows positive co-operativity in response to variations in phenylalanine concentration when assayed with the naturally occurring cofactor tetrahydrobiopterin. In addition, preincubation of phenylalanine hydroxylase with phenylalanine results in a substantial activation of the tetrahydrobiopterin-dependent activity of the enzyme. The monoclonal antibody PH-1 binds to phenylalanine hydroxylase only after the enzyme has been preincubated with phenylalanine and is therefore assumed to recognize a conformational epitope associated with substrate-level activation of the hydroxylase. Under these conditions, PH-1 inhibits the activity of phenylalanine hydroxylase; however, at maximal binding of PH-1 the enzyme is still 2-3 fold activated relative to the native enzyme. The inhibition by PH-1 is non-competitive with respect to tetrahydropterin cofactor. This suggests that PH-1 does not bind to an epitope at the active site of the hydroxylase. Upon maximal binding of PH-1, the positive co-operativity normally expressed by phenylalanine hydroxylase with respect to variations in phenylalanine concentration is abolished. The monoclonal antibody may therefore interact with phenylalanine hydroxylase at or near the regulatory or activator-binding site for phenylalanine on the enzyme molecule.

Synthetic mucin fragments. Methyl 6-O-(2-acetamido-2-deoxy-beta-D- glucopyranosyl)-beta-D-galactopyranoside, methyl 3,4-di-O-(2-acetamido-2-deoxy- beta-D-glucopyranosyl)-beta-D-galactopyranoside, and methyl O-(2-acetamido-2- deoxy-beta-D-glucopyranosyl)-(1----3)-O-beta-D-galactopyranosyl-(1---- 3)-O-(2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-beta-D-galactopyr ano side

Condensation of methyl 2,6-di-O-benzyl-beta-D-galactopyranoside with 2-methyl-(3,4,6-tri-O-acetyl-1,2-dideoxy-alpha-D-glucopyrano)-[2,1 -d]-2- oxazoline (1) in 1,2-dichloroethane, in the presence of p-toluenesulfonic acid, afforded a trisaccharide derivative which, on deacetylation, gave methyl 3,4-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2,6-di-O-benzyl-bet a-D- galactopyranoside (5). Hydrogenolysis of the benzyl groups of 5 furnished the title trisaccharide (6). A similar condensation of methyl 2,3-di-O-benzyl-beta-D-galactopyranoside with 1 produced a partially-protected disaccharide derivative, which, on O-deacetylation followed by hydrogenolysis, gave methyl 6-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-beta-D-galactopyranoside (10). Condensation of methyl 3-O-(2-acetamido-4,6-O-benzylidene-2-deoxy-beta-D- glucopyranosyl)-2,4,6-tri-O-benzyl-beta-D-galactopyranoside with 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-2,4,6 -tri-O-acetyl-alpha-D-galactopyranosyl bromide in 1:1 benzene-nitromethane in the presence of powdered mercuric cyanide gave a fully-protected tetrasaccharide derivative, which was O-deacetylated and then subjected to catalytic hydrogenation to furnish methyl O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-O-beta- D-galactopyranosyl-(1----3)-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl )- (1----3)-beta-D-galactopyranoside (15). The structures of 6, 10, and 15 were established by 13C-n.m.r. spectroscopy.

A human monoclonal macroglobulin with specificity for alpha(2----8)-linked poly-N-acetyl neuraminic acid, the capsular polysaccharide of group B meningococci and Escherichia coli K1, which crossreacts with polynucleotides and with denatured DNA

We have described an IgM antibody from a patient with macroglobulinemia specifically reacting with poly-alpha(2----8)N-acetyl neuraminic acid (NeuNAc) the capsular polysaccharide of two important human pathogens, group B meningococcus and E. coli K1. This antibody has a narrowly defined specificity in its interactions with polysaccharides, being unable to bind poly-alpha(2----9)NeuNAc or alternating poly-alpha(2----8)alpha(2----9)NeuNAc. However, it shows interesting crossreactivity with seemingly unrelated polynucleotides and denatured DNA, supporting the hypothesis that charged groups with a given spacing may determine the specificity of antigen-antibody interactions on otherwise dissimilar molecular structures. Despite the crossreactivity with denatured DNA and polynucleotides, the antibody does not appear to have adverse effects in the patient. The antibody protects newborn rats against E. coli K1 infection, as well as the standard horse antiserum H46, and one would expect it to prove useful in humans as an adjunct to antibiotic therapy in infections with group B meningococcus and E. coli K1. We have attempted to clone the antibody-producing cells from peripheral blood, and have shown that the relevant cells are present and can be cultured.

Immunochemical studies of mouse monoclonal antibodies to dextran B1355S--II. Combining site specificity, sequence, idiotype and affinity

The specificities of the combining sites of 19 mouse monoclonal antibodies to dextran B1355S have been characterized immunochemically by quantitative precipitin and precipitin inhibition assays; association constants for B1355S were determined by affinity gel electrophoresis. Cross-reactive and individual idiotypes related to the BALB/c B1355S-binding myeloma proteins MOPC104E [IdI(MOPC104E)] and J558 [IdI(J558)], determined by a radioimmunoassay, and heavy-chain variable-region sequences, are presented. Antibodies to B1355S are "alpha (1----3) alpha (1----6)-specific" as determined by precipitin and precipitin inhibition assays with dextrans and oligosaccharides, respectively, containing alternating alpha (1----3) alpha (1----6) linkages compared with oligosaccharides composed solely of alpha (1----3) or alpha (1----6) linkages; all antibodies have low association constants (less than or equal to 10(5) ml/g). However, there is also considerable diversity among the proteins as seen in the five groups of different patterns of reactivity with numerous dextrans having different structures, and the variability in affinity even among antibodies showing the same fine specificity by precipitin assay. There is little observable correlation of heavy-chain variable-region amino-acid sequence with specificity or affinity; however, all proteins having D-region amino acids Tyr,Asp at positions 96,97 express the MOPC104E individual idiotype and belong to precipitin specificity group 5, the group most cross-reactive with numerous dextrans, whereas those proteins having the J558 individual idiotype, Arg,Tyr or Asn,Tyr at 96,97 are found in all five precipitin groups.

The identification of antigenic determinants by a coupled inhibition-agar diffusion method

The determination of the chemical nature of immunodeterminant groups of carbohydrate antigens has been achieved by a micro method coupling inhibition and double diffusion in agar. This method has been tested with antigens which react with anti-lactose, anti-galactose, anti-N-acetyl-glucosamine and antirhamnose antibodies. The analysis can be performed with as little as 10 micrograms of inhibitor, 0.2 microgram of antigen and 10 micrograms of antibody. The procedure has also been used for the identification of the determinant groups of 2 antigens with a phosphoglycan structure. The determinants of these antigens have been found to be N-acetyl-beta-glucosamine 1-phosphate and beta-glucose 1-phosphate. The glycosyl 1-phosphate units are novel types of antigenic determinants and antigens with such determinants should be useful for investigating the interactions of antigens with homologous antibodies. The specificity of monoclonal antibodies directed at an O-antigen has been determined by use of the coupled method.

Synthetic mucin fragments: methyl 3-O-(2-acetamido-2-deoxy-β-d-glucopyranosyl)-β-d-galactopyranoside and methyl 3-O-(2-acetamido-2-deoxy-3-O-β-d-galactopyranosyl-β-d-glucopyranosyl)-β-d-galactopyranoside

Methyl 2,4,6-tri-O-benzyl-beta-D-galactopyranoside (5) was obtained crystalline by way of its 3-O-allyl derivative, which was in turn obtained by ring-opening of a presumed 3,4-O-stannylene derivative of methyl beta-D-galactopyranoside, followed by benzylation. Condensation of 5 with 2-methyl-(2-acetamido-3,4,6-tri-O-acetyl-1,2-dideoxy-beta-D-glucopyra no)-[2,1-d]-2-oxazoline in 1,2-dichloroethane in the presence of p-toluenesulfonic acid afforded the disaccharide derivative methyl 3-O-(2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-2, 4,6-tri-O-benzyl-beta-D-galactopyranoside (6) Deacetylation of 6 in methanolic sodium methoxide afforded the disaccharide derivative 7, which was acetalated with alpha, alpha-dimethoxytoluene to afford the 4',6'-O-benzylidene acetal (10). Catalytic hydrogenolysis of the benzyl groups of 7 afforded the title disaccharide 8. Glycosylation of 10 with 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in 1:1 benzene-nitromethane in the presence of mercuric cyanide gave the fully protected trisaccharide derivative 12. Systematic removal of the protecting groups of 12 then furnished the title trisaccharide 14. The structures of 5, 8, and 14 were all confirmed by 13C-n.m.r. spectroscopy. The 13C-n.m.r. chemical shifts for methyl alpha- and beta-D-galactopyranoside, and also those of their 3-O-allyl derivatives, are recorded, for the sake of comparison, in conjunction with those of compound 5.

Immunochemical characterization of the specificities of two human monoclonal IgM's reacting with chondroitin sulfates

We have studied the specificities of two human monoclonal, IgM containing sera, s/IgMMAC and s/IgMFIS, from patients with polyneuropathy. s/IgMMAC precipitates only with chondroitin sulfate C and not with A and B whereas s/IgMFIS is precipitated by chondroitins A, B (dermatan sulfate), and C. Inhibition assays using 2-acetamido-2-deoxy-3-O-(4-deoxy-beta-L-threo-hex-4-enopyranosyluroni c acid)-D-galactose and its 6- and 4-sulfate derivatives showed that the disaccharide 6-sulfate was the best inhibitor of precipitation of s/IgMMAC by chondroitin sulfate C, and the disaccharide 4-sulfate the best inhibitor of precipitation of s/IgMFIS by either chondroitin sulfates C or B. The nonsulfated disaccharide was a good inhibitor in each instance. D-Glucose 6-sulfate, Na2SO4, several sugar phosphates, and phosphate buffer also inhibited but to different extents with the s/IgMMAC and s/IgMFIS. All studies were carried out in 0.15M NaCl. The data indicate that both monoclonal proteins are antibodies comparable to the phosphorylcholine-binding myeloma proteins, and that the reactions show specificities above and beyond charge effects. The relation of various cross-reacting macromolecules to the monoclonal antibody was studied by diffusion in gels.

Evidence for solvent-induced conformational changes of the soluble Dunaliella chloroplast coupling factor 1 (CF1)

The ATPase activity of the chloroplast coupling factor 1 (CF1) isolated from the green alga Dunaliella is completely latent. A brief heat treatment irreversibly induces a Ca2+-dependent activity. The Ca2+-dependent ATPase activity can be reversibly inhibited by ethanol, which changes the divalent cation dependency from Ca2+ to Mg2+. Both the Ca2+-dependent and Mg2+-dependent ATPase activities of heat-treated Dunaliella CF1 are inhibited by monospecific antisera directed against Chlamydomonas reinhardi CF1. However, when assayed under identical conditions, the Ca2+-dependent ATPase activity is significantly more sensitive to inhibition by the antisera than is the Mg2+-dependent activity. These data are interpreted as indicating that soluble Dunaliella CF1 can exist in a variety of conformations, at least one of which catalyzes a Ca2+-dependent ATPase and two or more of which catalyze an Mg2+-dependent ATPase.

Synthesis of methyl 3-O- and 2-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-alpha D-galactopyranoside

Condensation of methyl 2-O-benzoyl-4,6-O-benzylidene-alpha-D-galactopyranoside with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl bromide (1) in dichloromethane, in the presence of silver trifluoromethanesulfonate, 2,4,6-trimethylpyridine, and molecular sieves, afforded methyl 2-O-benzoyl-4,6-O-benzylidene-3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalim ido- beta-D-glucopyranosyl)-alpha-D-galactopyranoside (4). Deacetalation of 4 in hot, 80% aqueous acetic acid gave methyl 2-O-benzoyl-3-O-(3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido- beta-D-glucopyranosyl)-alpha-D-galactopyranoside (5), which, on deacylation, followed by peracetylation, furnished the peracetylated disaccharide derivative (6). The structures of 5 and 6 were established by 1H-n.m.r. spectroscopy. O-Deacetylation of 6 afforded the title beta-(1 leads to 3)-linked disaccharide 7. For the synthesis of the beta-(1 leads to 2)-linked isomer, methyl 3-O-benzoyl-4,6-O-benzylidene-alpha-D-galactopyranoside was similarly condensed with bromide 1 to give the fully protected disaccharide derivative (8). Cleavage of the benzylidene group of 8 gave methyl 3-O-benzoyl-2-O-(3,4,6- tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-alpha-D- galactopyranoside (9). Deacetylation of 9, followed by peracetylation, afforded the peracetate (10). O-Deacetylation of 10 gave the beta-(1 leads to 2)-linked disaccharide (11). The structures of the disaccharides 7 and 11 were confirmed by 13C-n.m.r. spectroscopy.

Mapping epitopes on the insulin molecule using monoclonal antibodies

A panel of 18 monoclonal antibodies (mAb) delta to insulin have been prepared and used to begin to map antigenic determinants on the insulin molecule. All 18 mAb were of the IgG class, with 14 IgG1, 2 IgG2a and 2 IgG2b. The affinities of these mAb for their immunizing insulin ranged from 1 X 10(6) to 3 X 10(8) 1/M. The epitope recognized by three of the mAb, 1, 7 and 16 involves the three residues of the A chain, A 8-10, the so called A chain-loop determinant. This A chain loop is one of the most evolutionarily diverse regions of insulins from different species. Another mAb, 10, has been hypothesized to recognize a nearby epitope composed of the A chain residues, A4 and A8 and a B chain residue, B29, that are adjacent on the surface of the insulin molecule. Four of the mAb bind to synthetic B chain. The epitopes recognized by these 4 mAb and the last 10 mAb are unknown but the mAb are grouped according to their ability to bind to different species of insulin or proinsulin. The results of an 18 X 18 matrix analysis of pairs of mAb binding simultaneously to insulin indicate that, despite the finding that some mAb see similar antigenic sites on the insulin molecule, each of the mAb recognizes a unique site on the insulin molecule. Finally, a lower estimate of the number of possible antibodies made to insulin has been calculated to be greater than or equal to 115, a number only 10-fold lower than the lower limit of antibodies made to dinitrophenyl (DNP) or (4-hydroxy-5-iodo-3-nitrophenyl)acetyl (NIP), following hapten protein immunization.

Combining site specificities of mouse hybridoma antibodies to dextran B1355S

The combining sites of 12 mouse hybridoma antibodies to dextran B1355S have been characterized by quantitative precipitin assay. All antibodies preferentially bind the immunizing antigen B1355S and two other class I dextrans, B1498S and B1501S, but show substantial differences in the extents to which they cross react with class I dextrans, suggesting their clustering into five groups. Three myeloma proteins, CAL20 TEPC1035, J558, and MOPC104E, which bind dextran B1355S, each fall into a different group. There appears to be a substantial, but imperfect, correlation of DH region structure and individual idiotypic determinants with dextran binding patterns. Proteins with RY DH segments and IdI (J558) idiotypes are in groups 1 or 3, and proteins with YD DH segments and IdI (MOPC104E) idiotypes are exclusively in group 5. However, identical patterns of precipitin curves accompany very different sequences in CDR3. Antibodies of group 1, which react only with class II dextrans, differ the most in primary sequence, a finding suggesting that subsites responsible for cross reactivity with class I dextrans may be blocked and that this may be effected by side chains of different amino acids. This finding delineates a new aspect of the relationship of variability in amino acid sequence to antibody complementarity.