Immune response against the beta-galactosidase enzyme of E. coli at precursor cell level. I. Analysis of the secondary repertoire in BALB/c mice

Monoclonal antibodies in enzyme research: present and potential applications

Hybridoma antibodies are powerful tools. Their impact is already apparent in many areas of basic and applied research. In contrast, their impact is just beginning to be felt in enzymology. The existing literature on monoclonal antibodies to enzymes and isozymes, reviewed in this article, is as yet largely descriptive. However, the potential applications discussed herein promise to revolutionize existing strategies of unraveling the basic biochemistry, immunochemistry, and developmental, somatic cell, and molecular genetics of enzymes and isozymes. At a clinical level, monoclonal antibodies to enzymes promise to radically improve the current modalities of diagnosis and therapy in clinical enzymology and oncology. It is becoming increasingly apparent that the future applications of hybridoma antibodies to enzymes and isozymes appear to be limited only by our imagination.

Mitogen-reactive B cell subpopulations selectively express different sets of V regions

The experiments presented here were designed to investigate whether the idiotypic repertoire is equally distributed among B cells subpopulations as defined by mitogen reactivity. To this end we used lipopolysaccharides (LPS) and Nocardia delipidated cell mitogens (NDCM), which are two mitogens that have been described to act on different B cell subsets. The repertoire can be defined in quantitative terms as the frequency of B cells that are precursors for clones secreting immunoglobulin with a given specificity or with a determinate idiotype. We determined, therefore, the absolute frequency of LPS- and NDCM-sensitive B lymphocytes secreting immunoglobulin molecules that bear three idiotopes originally found on a monoclonal anti-beta galactosidase antibody. Because the frequencies of B cells carrying one of these idiotypes are dramatically different in the LPS- and NDCM-sensitive B cells subsets, we conclude that the idiotypic repertoire is not randomly distributed among mitogen-reactive B cell subpopulations.

Requirement of the immunogen (E. coli beta-galactosidase) for the response towards a determinant responsible for antibody-mediated enzyme activation, while antibodies binding some other site can be elicited by mitogen alone

Virgin mouse spleen cells cultured in vitro without antigen or mitogen produced a measurable amount of IgM binding E. coli beta-galactosidase (beta-gal). Lipopolysaccharide (LPS) and LPS plus antigen enhance this response, which cannot be considered truly polyclonal since it does not include the production of antibodies directed towards a conformation-dependent determinant, responsible for the activation of a mutant beta-gal, and known otherwise to be highly immunogenic. By priming in vivo with alum-treated beta-gal (unable to elicit activating antibodies), an activating response is obtained in vitro by LPS plus antigen, but not by LPS alone. These results are compatible with a two-signal requirement for the activation of B cells and may be explained as follows: (a) the mitogen, in absence of immunogen, stimulates those clones which have received a specific signal from cross-reacting structures in the environment: (b) instead, no cross-reaction are available for the conformation-controlled structure of the "activating" determinant; thus, intact immunogen is required as well as mitogen. Because of this "uniqueness", the molecule of beta-gal offers a highly specific tool to probe carrier-hapten relationships in native proteins.

Antibody-mediated activation of genetically defective Escherichia coli beta-galactosidases by monoclonal antibodies produced by somatic cell hybrids

Six hybridomas producing monoclonal antibodies against Escherichia coli beta-galactosidase (beta-D-galactoside galoctohydrolase, EC 3.2.1.23) have been derived from two separate somatic cell fusions. Three of these antibodies can activate defective enzymes produced by strains of E. coli carrying Z-gene point mutations. In antigen excess, one monoclonal antibody shows similar enzyme binding and mutant-activating capacity. Characteristically, the former reaction has a 200-fold higher equilibrium constant. These data provide direct evidence that the enzyme-activation reaction is a single-hit event in which one antibody site favors the correct conformation of one active center of the enzyme. Because each "activating" hybridoma is able to activate several but not all point mutant enzymes tested, it appears that the correction of the genetic defect is produced by binding key sites of the protein three-dimensional structure rather than the sites affected by the mutation.

Induction of antimyelin and antioligodendrocyte antibodies by vaccinia virus. An experimental study in the mouse

The appearance of serum antibodies binding to specific brain antigens was monitored in mice inoculated intracerebrally with a dermotropic or a neurotropic strain of vaccinia virus. Antibodies were measured with a binding assay using [125I]protein. A. Inoculation with the neurotropic strain caused an induction of serum antibodies binding to the myelin membrane, the myelin basic protein and oligodendrocytes while no induction of binding antibodies to neurons was observed. The dermotropic strain failed to elicit the formation of binding antibodies to brain antigens.

Somatic cell hybrids producing antibodies specific to human fibronectin

We have produced somatic cell hybrids between mouse plasocytoma cells deficient in hypoxanthine phosphoribosyltransferase (P3 x 63 Ag8) and spleen cells derived from mice immunized with purified human plasma fibronectin. We report herein the properties of monoclonal anti-fibronectin antibodies released by eight different clones.

Monoclonal antibodies specific for carcinoembryonic antigen and produced by two hybrid cell lines

Spleen cells from mice immunized with purified carcinoembryonic antigen (CEA), an important tumor marker of human carcinomas, were fused with the mouse myeloma cell line P3-NSI/1-Ag4. Out of the 400 hybrids obtained, 2 secreted antibodies reacting specifically with two different antigenic determinants present on CEA molecules. They were cloned and established as permanent hybridoma cell lines. These antibodies, which have relatively high-affinities and can be produced in unlimited amounts, will be useful both for the immunochemical characterization of CEA and as a standard reagent for the identification of this antigen in human tissues and body fluids.

Fibronectin: a chromatin-associated protein?

We have previously reported that chromatin preparations from human cultured fibroblasts contain a single homologous serum protein. In this paper we present evidence, based on immunological identity and physicochemical properties, that this serum protein is fibronectin. Furthermore, using a radioimmunoassay system, we have estimated that fibronectin represents about 0.7% of the total protein in both chromatin preparations and whole fibroblasts. Using a nitrocellulose filter assay system, we also show that fibronectin is a DNA-binding protein having an equilibrium constant of 4.6 x 10(-6) M. Equilibrium competition experiments have demonstrated that fibronectin has the ability to differentiate among nucleotides, indicating that fibronectin-DNA interaction is at least partially specific, and that a minimum polymer length of 12-18 nucleotides is required for effective binding to occur. Fibronectin has been isolated readily from plasma using DNA-affinity chromatography. We do not have direct evidence that fibronectin is an actual nonhistone chromosomal protein, but fibronectin is a DNA-binding protein (at least under in vitro assay conditions) and appears to be a normal constituent of chromatin as chromatin is currently isolated from cell nuclei.