Adaptation of the slide immunoenzymatic assay for quantification of DNA hybridization: SIA-DNA

A quantitative, non-radioisotopic microsystem has been developed for measuring nucleic acid hybridization using microliter volumes of test sample and reagents. This new method, Slide Immunoenzymatic Assay-DNA, is a modification of the Slide Immunoenzymatic Assay technology originally designed for quantifying antigens and antibodies. It features small, circular solid phases (circles) of transparent material for nucleic acid immobilization. This allows the use of enzyme-labelled gene probes and substrates that generate color which, due to the distribution pattern of the circles on their support, can be measured by automated microtitration plate readers. Slide Immunoenzymatic Assay-DNA has been standardized to measure hybridization of probe to purified DNA or to DNA in cells lysed directly on the circles. Owing to its simplicity, relative low cost and expeditiousness, i.e., providing results in four hours. Slide Immunoenzymatic Assay-DNA is also suitable for use in simple laboratories and field studies.

Isolation and Characterization of Methanogenic Bacteria from Landfills

Methanogenic bacteria were isolated from landfill sites in the United Kingdom. Strains of Methanobacterium formicicum, Methanosarcina barkeri , several different immunotypes of Methanobacterium bryantii , and a coccoid methanogen distinct from the reference immunotypes were identified.

Monoclonal antibodies against bacteria

Highlights are presented of most recent work in which monoclonal antibodies have been instrumental in the study of bacteria and their products. Topics summarized pertain to human and veterinary medicines, dentistry, phytopathology, ichthyology, and bacterial ecophysiology, differentiation, evolution and methanogenic biotechnology.

Slide immunoenzymatic assay (SIA): improving sensitivity to measure antibodies when samples are very small and dilute, and antigen is scarce

Modifications to the slide immunoenzymatic assay (SIA) using the PAP reagent (SIA-PAP) were developed which increase sensitivity considerably. These SIA modifications are particularly useful for measuring speedily antibodies in dilute samples available only in microliter-volumes when antigen is scarce, whether a molecule, or a prokaryotic or eukaryotic cell.

Antigenic distinctiveness, heterogeneity, and relationships of Methanothrix spp

A detailed immunologic analysis of Methanothrix soehngenii Opfikon (the type species of the genus), Methanothrix sp. strain CALS-1, and Methanothrix concilii GP6 was performed. A variety of poly- and monoclonal antibody probes for a comprehensive panel of reference organisms were used to determine immunogenicity, antigenicity, and relationships. The three organisms are antigenically distinct but interrelated, forming an immunologically cohesive group, weakly related to methanosarcinae. A prominent feature of the organisms was heterogeneity characterized by antigenic diversity and compartmentation, the latter particularly evident in M. soehngenii Opfikon, which was examined more thoroughly. The complexity of the antigenic profile of this strain and the heterogeneity of the group suggest a high degree of phenotypic diversification within the genus.

Multiple solid-phase system for storage of dry ready-for-use reagents and efficient performance of immunoenzymatic and other assays

A modular system of independent but matching solid phases coated with the reagents for the slide immunoenzymatic assay (SIA) was developed. Antigen, antiserum, second antibody labeled with enzyme, and substrate are immobilized as dry films onto circles surrounded by a hydrophobic material on separate glass slides. The reagents stay on the circles ready for use for at least 1 year. Circles coated with the two reagents involved in each step of the assay are approximated to one another by pairing slides, one on top of the other. Hinged slide frames ensure exact superposition of circles with matching reagents separated by a gap 1 mm thick. This is occupied by a liquid column that forms from a 10 microliters drop of water or buffer pre-deposited onto the circles of the bottom slide. The liquid bridge provides the milieu for interaction of reagents. Pairs of slides are incubated as needed for each step. The enzymatic reaction of the last step is read with a vertical beam spectrophotometer. The same multiple-phase system can be used for immunofluorescence. Reactions occur faster using the system than when reagents are admixed in solution.

Antigenic mosaic of Methanogenium spp.: analysis with poly- and monoclonal antibody probes

Eight well-characterized Methanogenium strains, including the six described type strains, were analyzed with poly- and monoclonal antibody probes to examine the antigenic mosaic of the genus. The pattern of cross-reactions showed that the mosaic is complex and varies with the strains; thus, these organisms have developed a considerable antigenic diversity, which is expressed in their envelopes. Every strain shared at least one determinant with at least one other strain, demonstrating the antigenic cohesiveness of the group. This finding, together with the fact that most strains displayed a distinctive antigenic fingerprint (notwithstanding the limited number of probes available), emphasizes the potential of antibodies for rapid identification of new isolates and for direct elucidation of Methanogenium strains in microbial mixtures.

Immunologic distinctiveness of archaebacteria that grow in high salt

The antigenic fingerprints of eight halophilic archaebacteria representing the groups recently outlined by molecular and chemical analyses were determined with calibrated antibody probes. Comparison with the antigenic fingerprints of methanogens encompassing all described families and most genera demonstrated that these two archaebacterial groups are themselves antigenically coherent but immunologically distinct.

Slide immunoenzymatic assay for human IgE (SIA-IgE)

A rapid and inexpensive method is described for determination of human serum IgE using 5-microliter samples. The slide immunoenzymatic assay for IgE (SIA-IgE) is carried out on a glass slide in which up to 24 samples can be tested including controls and standards; up to four of these slides can be read automatically in conventional vertical beam readers. Flat circles on the slide are covered with a layer of biotinylated antibody specific for human IgE (trapping antibody). Five microliters of serum sample is dropped to cover each circle, and the slide is incubated. The circles are washed with water, dried, incubated under 10 microliters of enzyme-labeled antibody to human IgE, then washed again, and covered with 10 microliters of enzyme substrate. The intensity of color generated is measured at the proper wavelength. The method is simple, accurate and non-radioactive and can be completed within 2 h.

Monoclonal antibodies for bacterial identification and taxonomy: 1985 and beyond

Contemporary bacterial serology relevant to medicine involves poly- and monoclonal antibodies to study pathogenic bacteria and nonpathogenic organisms useful in controlling infectious diseases. Monoclonal antibody applications include immunodiagnostics, prophylaxis and serotherapy, and microbial biotechnology and molecular immunochemistry. If used in parallel with antisera, the analytic potential of monoclonal antibodies is better realized. However, the entire range of advantages from the use of monoclonal antibodies can only be attained if the antibodies are well characterized.

Comparative analysis of rat uterine estrogen-induced creatine kinase with monoclonal antibodies

Monoclonal antibodies were generated against rat uterine estrogen-induced protein--creatine kinase (CK-EIP)--and two (MAb-28 and MAb-78) were studied. These antibodies were IgM but differed in their complementary antigenic determinants both of which were detectable on denatured but not on native CK-EIP. MAb-28 reacted with other CK-BBs but not with CK-MMs whereas MAb-78 reacted with both types of CKs. A measurement of antigenicity with the monoclonal antibodies under calibrated conditions showed differences among the CKs, notably between CK-BB from rat brain and CK-EIP when both were probed with MAb-28. The antigenicity of CK-BB (rat brain) was significantly lower than that of CK-EIP, indicating that the former either expresses less copies of the determinant recognized by MAb-28 than CK-EIP does, or possesses a determinant which interacts with the antibody with lower affinity. The monoclonal antibodies should help elucidate structure-function relationships in CK-BB and CK-EIP molecules, their anatomic distribution and their physiologic, pathologic and experimental variations in relation to gene expression induced by sex hormones.

Slide immunoenzymatic assay for immunoglobulin isotype (SIA-Ig)

A simple method is described for rapid determination of immunoglobulin class and subclass in an assortment of samples based on the slide immunoenzymatic assay (SIA-Ig). Each circle on a multi-circle glass slide is coated with anti-immunoglobulin class or subclass antibody. For each isotype to be assayed a circle is coated with its specific anti-isotype. The coated circles are incubated with sample containing the immunoglobulin(s) of unknown isotype and are then washed. The slide is then incubated with enzyme-labeled anti-immunoglobulin and washed again. Finally, enzyme substrate is deposited onto the circles. Color appears within a few minutes only on the circle where the unknown was bound specifically by its corresponding anti-isotype antibody. The method reveals correctly the isotype of the constituents of complex mixtures, such as serum, as well as that of the only component of samples containing a single molecular species of immunoglobulin (e.g., monoclonal antibodies). The method is simple, reliable, gives results in less than 1 h and is adequately sensitive for a wide range of practical applications.

Six antigenic determinants in the surface layer of the archaebacterium Methanococcus vannielii revealed by monoclonal antibodies

The immunogenicity and antigenic characteristics of the unique surface layer (S layer) of Methanococcus vanielii was studied with a panel of six monoclonal antibodies. Six surface determinants were identified for the first time, each recognized by one antibody exclusively. The determinants are proteins, located in the S layer, and accessible to antibody in whole, unfixed, as well as formalinized bacteria. Hence the six antigens and antibodies reported here should be useful for rapid identification of new isolates and for taxonomy of methanogens, notably Methanococcaceae. In this connection two novel applications of the slide immunoenzymatic assay were developed for analyses of monoclonal antibodies and their complementary sites in the bacterial envelope.

Six antigenic determinants in the surface layer of the archaebacterium Methanococcus vannielii revealed by monoclonal antibodies

The immunogenicity and antigenic characteristics of the unique surface layer (S layer) of Methanococcus vanielii was studied with a panel of six monoclonal antibodies. Six surface determinants were identified for the first time, each recognized by one antibody exclusively. The determinants are proteins, located in the S layer, and accessible to antibody in whole, unfixed, as well as formalinized bacteria. Hence the six antigens and antibodies reported here should be useful for rapid identification of new isolates and for taxonomy of methanogens, notably Methanococcaceae. In this connection two novel applications of the slide immunoenzymatic assay were developed for analyses of monoclonal antibodies and their complementary sites in the bacterial envelope.

Antibacterial monoclonal antibodies and the dawn of a new era in the control of infection

Literature reports concerned with monoclonal antibodies against bacteria, or their toxins, which are pathogens for man and animals were surveyed. These antibodies have important potential uses in human and veterinary pathology and medicine. They are likely to become key elements in a fast progression toward a more complete understanding and control of infectious diseases and of toxin poisoning. A new area of bacteriology relevant to sanitary engineering is also being advanced with the help of antibacterial monoclonal antibodies. This area involves bacteria that produce the biofuel methane, along with other molecules of nutritional value, through a process which brings about the recycling of organic wastes and thereby limits or controls microbial contamination of soil and water.

Dissecting the antigenic mosaic of the Archaebacterium Methanobacterium thermoautotrophicum by monoclonal antibodies of defined molecular specificity

The antigenic mosaic of the Archaebacterium Methanobacterium thermoautotrophicum, strain delta H, was analyzed with a panel of six monoclonal antibodies. Five antigenic determinants were identified. One contains N-acetyl-D-glucosamine, another contains N-acetyl-D-galactosamine, and a third contains gamma-glutamylalanine (gamma-Glu-Ala). These residues are not involved, at least as immunodominant epitopes, in the other two determinants, one of which contains L-talosaminuronic acid, a component of pseudomurein found only in Methanobacteriaceae. Each of the five determinants was recognized by one monoclonal antibody exclusively. A sixth antibody recognized a structure containing gamma-Glu-Ala that could be either a sixth determinant or a subdeterminant within the site already recognized as containing gamma-Glu-Ala. We postulate that two of the determinants are strain specific, three are species specific, and one is a common antigen.

Quantitative slide micro-immunoenzymatic assay (micro-SIA) for antibodies to particulate and non-particulate antigens

A quantitative, minimized version of the slide immunoenzymatic assay (SIA) is described, which is performed with a 5 microliters drop of each reagent on a circular glass surface (3 mm in diameter) delimited by a thin layer of a hydrophobic material. Measurements are done directly, without disturbing the drop of substrate solution while the enzymatic reaction takes place, by means of a vertical beam spectrophotometer. The main features of this quantitative micro-SIA are its simplicity, reproducibility, virtual absence of background and applicability to a large variety of antigen-antibody systems.

Antigenic analysis of Methanomicrobiales and Methanobrevibacter arboriphilus

Preparation of new antisera has permitted more comprehensive immunological analyses of the two families of Methanomicrobiales. Methanomicrobiaceae and Methanosarcinaceae, and the species Methanobrevibacter arboriphilus. Immunological analysis was carried out with antibody probes against 23 strains, including almost all genera and species of methanogens. The absence of cross-reactions between families of methanogens was confirmed. Methanomicrobium and Methanogenium were found to be immunologically related. Extensive cross-reactions occurred among six strains of Methanosarcinaceae, but none occurred among three strains of M. arboriphilus when tested with the S probe, i.e., the last antiserum dilution of the titration curve's plateau.

Monoclonal antibodies for immunochemical analysis of methanogenic bacteria

Sixty-nine hybridomas were generated to produce monoclonal antibodies to species of methanogens representing three of the four families accepted at the present time: Methanobacteriaceae, Methanococcaceae, and Methanomicrobiaceae. The antibody of each of 29 hybridomas cross-reacted with a methanogen of the same species or genus as the immunizing (homologous) strain, whereas the antibody of the other 40 cell lines reacted only with the homologous strain. Inhibition-blocking experiments with compounds of known composition and structure were used to define the fine specificity of antibodies of four hybridomas representing the four genera of the methanogens used for immunization. The combining site of the monoclonal antibody against M. thermoautotrophicum delta H examined is specific for a structure in the pseudomurein involving N-acetyl-glucosamine but not the (1-3) linkage or the C-terminus gamma-Glu-Ala of the peptide, both of which are characteristic of pseudomurein, the cell-wall peptidoglycan distinctive of the Methanobacteriaceae. In contrast, the monoclonal antibody to the other methanogen of this family examined, M. arboriphilus DH1, recognizes a determinant involving gamma-Glu-Ala. Thus pseudomurein expresses at least two dissimilar antigenic determinants in different portions of the molecule. The monoclonal antibodies against M. vannielii SB and M. hungatei JF1, whose families do not possess pseudomurein, did not display specificity for analogues of pseudomurein.

Monoclonal antibodies for immunochemical analysis of methanogenic bacteria

Sixty-nine hybridomas were generated to produce monoclonal antibodies to species of methanogens representing three of the four families accepted at the present time: Methanobacteriaceae, Methanococcaceae, and Methanomicrobiaceae. The antibody of each of 29 hybridomas cross-reacted with a methanogen of the same species or genus as the immunizing (homologous) strain, whereas the antibody of the other 40 cell lines reacted only with the homologous strain. Inhibition-blocking experiments with compounds of known composition and structure were used to define the fine specificity of antibodies of four hybridomas representing the four genera of the methanogens used for immunization. The combining site of the monoclonal antibody against M. thermoautotrophicum delta H examined is specific for a structure in the pseudomurein involving N-acetyl-glucosamine but not the (1-3) linkage or the C-terminus gamma-Glu-Ala of the peptide, both of which are characteristic of pseudomurein, the cell-wall peptidoglycan distinctive of the Methanobacteriaceae. In contrast, the monoclonal antibody to the other methanogen of this family examined, M. arboriphilus DH1, recognizes a determinant involving gamma-Glu-Ala. Thus pseudomurein expresses at least two dissimilar antigenic determinants in different portions of the molecule. The monoclonal antibodies against M. vannielii SB and M. hungatei JF1, whose families do not possess pseudomurein, did not display specificity for analogues of pseudomurein.

The immunology of methanogens: a new development in microbial biotechnology

The immunology of methanogens is an important area of research into biotechnology-bioengineering involving these bacteria. Here, recent findings regarding the antigenic characteristics of methanogens are discussed, emphasizing the present availability of antibody probes and immunological methods for their identification, classification, and structural analysis.

Antibody analysis of relationships among methanogenic bacteria

A bank of antisera to the majority of methanogenic bacteria is now available. Three antibody probes, R, S, and T, were derived from each antiserum in the bank and used for analysis of antigenic relatedness among methanogens by immunofluorescence. The T probe reacted only with the immunizing (or homologous) strain, the S probe gave strong cross-reactions with strains of the same species, and the R probe revealed some interspecies relationships. The results were confirmed and extended by enzyme immunoassays and standard serological methods involving serial dilution analysis, cross-adsorptions, and the use of reference strains. The immunological methods and standardized antibody probes are useful for rapid identification of methanogens and measurements of antigenic relationships which aid in the classification of these bacteria.

Specific antisera and immunological procedures for characterization of methanogenic bacteria

Specific antisera were raised in rabbits to 19 methanogenic bacteria representing the species available in pure culture at the present time. The antisera were characterized, labeled, and organized in a bank to serve as a source of material for preparation of antibody probes and thus provide standardized reagents for immunological analysis of methanogens. An indirect immunofluorescence procedure was standardized for optimal staining of homologous and heterologous bacterial strains. Two immunoenzymatic assays were developed: (i) a simple slide assay, useful for rapid antibody detection in small samples, antibody titrations, and disclosure of cross-reactions among methanogens, and (ii) a quantitative method. The latter is useful for quantification of antigenic relatedness. Procedural details were developed to obtain optimal bacterial preparations for use as immunogens to raise antibodies in vivo, and as antigens for antibody assay in vitro.

Isolation of Methanobrevibacter smithii from human feces

Fecal specimens from nine adults were examined for the presence of methanogenic bacteria. Enrichment cultures of five specimens produced methane in 5 days. Of these five specimens, three were tested and produced methane during a short-term incubation. Four specimens did not produce methane in either short-term incubation or in enrichment culture. Each methanogenic culture contained methanogens similar in morphology to organisms of the genus Methanobrevibacter and showed factor-420 fluorescence by fluorescence microscopy. Pure cultures were obtained from four of the five methanogenic enrichment cultures. Each isolate grew and formed methane from either H2-CO2 or formate, but growth obtained with formate was poor. None of the isolates used acetate, methanol, or trimethylamine. All isolates grew in the presence of bile salts. In immunological studies, each isolate was closely related to the type strain of Methanobrevibacter smithii, a finding consistent with the physiological and morphological similarities between the isolates and the type strain.

Immunology of archaebacteria that produce methane gas

The antigenic map of 17 methanogenic bacteria representing the entire range of available species was determined by multiple assay with antibody probes. Four major clusters of antigenically related strains coincide with the females proposed on the basis of 16S ribosomal RNA analysis. Immunological mapping uncovered relationships not yet shown by other methods and allowed identification and classification of two new bacterial isolates.

Specific antigen-binding molecules in normal serum. A quest for circulating receptors

Molecules (I) in the IgM fraction of normal serum compete with specific antibody for a single determinant on a macromolecule. Following immunization, the levels of I fall as antibody titer rises, but they later increase again during the decline of antibody. These findings are discussed in light of recent studies regarding soluble antigen-specific factors.

Purification of erythroblastic nests

We describe a method for preparing purified erythroblastic nests in large numbers (approximately 10(6)/run) in three steps: (1) induction of splenic erythropoiesis in mice, (2) preparative differential centrifugation for the removal of erythrocytes and single cells from spleen cell suspensions, and (3) sedimentation in an isokinetic gradient of Ficoll 400 in Joklik's modification of minimum essential medium. Viability of isolated EN is very high, as demonstrated by the trypan blue exclusion and in vitro erythrocyte formation methods.

Phenotypic diversification of a cultured tumor line as a function of substratum

We have found that a murine hepatoma displays a considerable phenotypic diversification in culture, which depends upon the substratum utilized, and is manifested by the formation of multicellular structures of differing geometry: Monolayer on glass and plastic, thick multilayer pads on Gelfilm, and spheroids on agar and agarose. These multicellular morphological phenotypes were assayed without disruption to ascertain their antigenicity in vitro and their tumorigenicity in vivo and to obtain quantitative information on the effect of the spatial arrangement of the hepatoma cells upon the ability of each multicellular structure to interact, as a whole, with molecules and cells in its surroundings. The antigenicity of the multicellular structures was determined with calibrated probes and a methodology that measures the total antigenicity, as well as antigenicity per unit of surface area. Antigenicity was found to differ in the following decreasing order: Monolayer on plastic greater than spheroids on agarose greater than spheroids on agar greater than multilayer on Gelfilm. At least part of these antigenic variants arise from different degrees of masking of the structures' surface determinants by a trypsin-sensitive material. The multicellular phenotypes also differed in tumorigenicity. When assayed in syngeneic hosts under comparable conditions, agar-grown spheroids produced the fewest tumors, whereas Gelfilm-grown multilayers produced the most. These two independent sets of data show that the various geometries that a tumor tissue is induced to acquire by the culture substratum are accompanied by a distinctive combination of surface and biological properties.

Lymphocyte subpopulations and function in chronic murine toxoplasmosis

A long-lasting, chronic infection with Toxoplasma gondii was established in C57Bl/6J mice as a model system of slow parasite infection. We quantified all nucleated cells and Thy-1+ and Thy-1- cell subpopulations in thymus, spleen and peripheral and mesenteric lymph nodes throughout the first 8 months of life of mice infected at 8 weeks of age. We found a physiological pattern of change with age in the lymphocyte subpopulations examined; the pattern was distinctive for each lymphoid organ. These normal patterns were altered in infected mice from the beginning of the observation period. The most prominent findings were (a) a relatively early atrophy of the thymus and (b) no increase in Thy-1+ lymphocyte numbers in either spleen or lymph nodes during the first 3 months post-infection, followed by decreasing numbers afterwards. Other findings were a rapid increase in the number of Thy-1- cells in the thymus before the onset of generalized atrophy; accumulation of erythrocytes in the spleen and splenomegaly during the first 3 months post-infection, despite a steady decrease in the number of nucleated cells; and an increase in Thy-1- cells in the peripheral but not in the mesenteric nodes, thereby diluting the Thy-1+ lymphocyte subpopulation.

Immunosuppression associated with erythropoiesis in genetic low responder mice

Priming-memory generation in response to Escherichia coli beta-D-galactosidase occurs without antibody formation in irradiated spleen-cell-transferred C57BL/6J mice, which are genetic low responders to the enzyme. Erythropoiesis abolishes priming-memory generation, so that recipients immunized a few days after cell transfer and erythropoiesis induction do not mount a secondary antibody response. Priming-memory generation in cell recipients immunized 3 days after erythropoiesis induction was less frequent than in controls, whereas no significant differences were found when antigen was given before erythropoiesis induction or 5 days after it. The mean titre of the mice escapint suppression was similar to that of the control mice, which became primed and mounted memory. The titre distribution in both responder groups were also similar, although no high-titered responders were found in the erythropoietic mice. Thus while erythropoiesis induction affects the frequency of priming-memory generation, it does not affect to the same extent the amount of memory generated in those mice escaping suppression. The same distinction was observed when spleen cells from erythropoietic mice, containing 30 to 40% erythroblasts, were transferred into normal mice. However, induction of erythropoiesis in non-irradiated non-cell=transferred mice did not cause suppression.

Specific inhibition of the antibody-mediated activation of a defective beta-D-galactosidase by circulating activating epitope-binding molecules

Activation of a defective Escherichia coli beta-D-galactosidase by specific activating antibody is inhibited competitively by a molecule with immunoglobulin properties but devoid of activating capacity. This molecule is found in the serum of nonimmunized rabbits and is no longer detectable after beta-D-galactosidase administration, but can be demonstrated in rabbits injected with antigens other than the enzyme. The data show that the inhibitory molecule recognizes and interacts specifically with the activating epitope of the activatable enzyme and that, although unable to activate the latter, it competes with the activating antibody and inhibits activation.

New bioassay for screening immunotoxic agents

A new bioassay for evaluation of compounds potentially toxic for the immune system is described. It is suitable for the measurement of enhancement of primary antibody response and of enhancement and inhibition of memory development in vivo. It utilizes immunoenzymatic techniques which can readily be automated and thus allow the screening of many compounds at relatively low cost. It can provide answers regarding the safety or danger of each compound tested within 30-45 days.

Deficiency of high-affinity anti-beta-D-galactosidase antibodies in selected low immune responder mice

Amount and affinity of anti-beta-D-galactosidase-activating antibodies (AAb) were studied in two lines of mice obtained by selective breeding for antibody response to heterologous erythrocytes. These lines, referred to as high (H) and low (L) lines, differ also in their responses to many antigens. Concerning AAb amounts, the maximal titer in H mice is higher than in L mice. However, the AAb levels in H mice decreased with increasing immunizing doses and became lower than in L mice for the highest dose. This fact can be explained in terms of intramolecular competition or suppression. Whereas the usual maturation pattern was observed in H mice, no AAb of high affinity were found in L mice, even after a minimal immunizing dose. At any dose tested, no maturation of AAb occurred until three months after immunization. This deficiency may be ascribed to B lymphocyte or macrophage modifications. A correlation between the deficiency of high-affinity AAb in L mice and their genetically induced low antibody responsiveness cannot be proved.

Long-term antibody synthesis in vitro. VI. Anti-allotype sera as probes of clonal products in affinity maturation

A new experimental system is described for measuring the allotypic product of rabbit B cells during long-lasting in vitro antibody responses. The immunoenzymatic assays described allow determination of several parameters mapping in different regions of the same molecule, which can be measured and combined to yield a multidimensional picture of the time-course dynamics of antibody synthesis. The rabbit immune system responding to Escherichia coli beta-D-galactosidase was sample and disassembled by (a) culturing lymph node microfragments and (b) sorting out from among all anti-enzyme antibodies only those activating a mutant enzyme, AMEF, which bore the b4 or b9 allotype. A considerable simplification of the response was achieved in the microcultures as documented by cultures of heterozygous cells which produced only one allotype and by the fact that each culture showed a distinctive pattern when antibody titre, association constant, heterogeneity index, L-chain type, and k-chain allotype were considered together. This array of patterns was not an artifact but the result of disassembling a representative sample of the rabbit immune system into small components, since the b4/b9 ratio obtained by averaging the results of all cultures from a heterozygous rabbit lymph node was the same as the serum ratio. Despite the Poisson distribution of the responder microcultures, none of them was monoclonal; i.e. no antibodies homogeneous by all parameters tested were observed, This finidng supports the notion that in normal lymphoid tissue in its native tridimensional arrangement, one T cell can trigger several B cells clustered in one antibody-forming unit. This natural arrangement would ensure the monospecificity of the cluster (dictated by the T cell) while allowing for variation in affinity (depending upon the array of B cells in the unit). Accordingly our findings would results from the fact that as the size of the microfragments was reduced, the cells diluted out first were T cells, but as long as one of them was present, several B-cell clones were triggered. The b4/b9 pattern of any given culture remained constant over several months, but the ratio kappa/lambda underwent changes. An increase in molecules with non kappa-chains (which could not be reacted with anti-kappa-chain allotype antisera) was usually associated with a parallel decrease in antibody affinity. This occurred by the end of the antibody cycle and might be related to the regulation of antibody synthesis by T-cell suppressor factors.