CXC chemokine receptor 5 expression defines follicular homing T cells with B cell helper function.

Leukocyte traffic through secondary lymphoid tissues is finely tuned by chemokines. We have studied the functional properties of a human T cell subset marked by the expression of CXC chemokine receptor 5 (CXCR5). Memory but not naive T cells from tonsils are CXCR5(+) and migrate in response to the B cell-attracting chemokine 1 (BCA-1), which is selectively expressed by reticular cells and blood vessels within B cell follicles. Tonsillar CXCR5(+) T cells do not respond to other chemokines present in secondary lymphoid tissues, including secondary lymphoid tissue chemokine (SLC), EBV-induced molecule 1 ligand chemokine (ELC), and stromal cell-derived factor 1 (SDF-1). The involvement of tonsillar CXCR5(+) T cells in humoral immune responses is suggested by their localization in the mantle and light zone germinal centers of B cell follicles and by the concomitant expression of activation and costimulatory markers, including CD69, HLA-DR, and inducible costimulator (ICOS). Peripheral blood CXCR5(+) T cells also belong to the CD4(+) memory T cell subset but, in contrast to tonsillar cells, are in a resting state and migrate weakly to chemokines. CXCR5(+) T cells are very inefficient in the production of cytokines but potently induce antibody production during coculture with B cells. These properties portray CXCR5(+) T cells as a distinct memory T cell subset with B cell helper function, designated here as follicular B helper T cells (T(FH)).

Role of repetitive antigen patterns for induction of antibodies against antibodies.

Antibody responses against antibodies, such as rheumatoid factors, are found in several immunopathological diseases and may play a role in disease pathogenesis. Experience shows that they are usually difficult to induce experimentally. Antibodies specific for immunoglobulin constant regions (anti-allotypic) or for variable regions (anti-idiotypic) have been investigated in animal models; the latter have even been postulated to regulate antibody and T cell responses via network-like interactions. Why and how such anti-antibodies are induced during autoimmune diseases, has remained largely unclear. Because repetitively arranged epitopes in a paracrystalline structure of a viral envelope cross-link B cell receptors efficiently to induce a prompt T-independent IgM response, this study used immune complexes containing viruses or bacteria to evaluate the role of antigen pattern for induction of anti-antibody responses. We present evidence that antibodies bound to strictly ordered, but not to irregularly arranged, antigens dramatically enhance induction of anti-antibodies, already after a single immunization and without using adjuvants. The results indicate a novel link between anti-antibody responses and infectious agents, and suggest a similar role for repetitive self-antigens such as DNA or collagen involved in chronic immunopathological diseases.

Actin III and myofilaments in different muscles of wildtype and the mutant raised of Drosophila melanogaster.

The mutation raised (rsd, 3-95.4) of Drosophila melanogaster causes flightlessness as a consequence of abnormalities in the fibrillar flight muscles (FFMs). In this muscle type actin III is neither synthesized nor accumulated while adult tubular muscles of rsd flies are indistinguishable from wildtype. This paper demonstrates ultrastructural defects in rds FFMs and extends the biochemical comparison of adult wildtype and rsd muscles to larval muscles and to embryo cells differentiating in culture. The FFMs of mature rsd flies contain thick filaments in irregular bundles, but no thin filaments. Normal Z-discs are virtually absent. Instead, a large number of Z-disc residues are present in stacks attached to short filaments on either side. In newly emerged rsd flies the disorganization is less pronounced. The adult tubular muscles and the supercontracting muscles of third-instar larvae of rsd can ultrastructurally not be distinguished from wildtype. The present biochemical results indicate that not only FFMs of mature and newly emerged adults are affected by the rsd genotype. Synthesis of actin III is not detectable in rsd FFMs which corresponds to the heavy structural defects. In addition to the lack of actin III synthesis in rsd FFMs, three unidentified proteins (52 kDa, 80 kDa, 90 kDa) which are specific for wildtype FFMs are also not synthesized in rsd flies. Among all other muscle types studied, all of which are morphologically unaffected, only adult tubular muscle of rsd genotype showed no biochemical effect. Larval supercontracting muscle as well as embryo cells differentiating in culture failed to synthesize actin III in the case of rsd cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective generation of antigen-specific human hybridomas optimized for large scale growth in serum-free medium.

The direct propagation of newly formed human hybridomas in serum-free medium selects for hybrids with a metabolism best suited to growth in this environment. Under optimal culture conditions, this procedure results in the generation of antigen-specific human hybridomas comparable in frequency, stability, and antibody secretion rate to that obtained with murine hybridomas. After a transient phase of a few days in the appropriate selection medium supplemented with 1% serum, hybridomas grow in serum-free medium in stationary cultures with a cell doubling time of 15-25 h and an antibody production rate averaging 12 micrograms/10(6) cells/day. Clones propagated in bioreactors exhibited a cell doubling time of 29-35 h and an antibody secretion rate of 10-21 micrograms/10(6) cells/day.

Qualitative analysis of antibody binding. An in vitro assay for the evaluation and development of vaccines.

We describe a rapid in vitro assay for the evaluation of in vivo properties of conjugate vaccines. Using human and murine monoclonal antibodies (mAb) specific for lipopolysaccharides (LPS), isolated from Pseudomonas aeruginosa, we determined in a competitive binding assay the amount of LPS or conjugate vaccine which was required to inhibit the antibody binding to LPS by 50% (I50 values). Furthermore, utilizing a murine burn wound sepsis model, we determined the potential of the same conjugates to induce protection in vivo against infection with the corresponding bacteria. Protective mAb have approximately 100-fold lower I50 values for preparations which are highly effective in inducing protection than for preparations which are ineffective. Furthermore, in the case of potent preparations it was noted that protective mAb exhibit similar I50 values for the conjugates and for the corresponding LPS. These results suggest that the fast and easily interpretable in vitro assay described may significantly facilitate the development and optimization of vaccines.

Analyses of affinity distributions within polyclonal populations of antigen-specific antibodies. Evaluation of their accuracy in population detection using monoclonal antibodies.

The potential of an ELISA based detection of affinity distributions within polyclonal populations of antigen-specific serum antibodies was assessed by analyzing defined probes composed of monoclonal antibodies (MAb). In a competitive binding ELISA in which the concentration of antigen in the liquid phase and the solid phase was varied, we analyzed mixtures containing defined percentage compositions of MAb exhibiting apparent affinity constants (aK) between 3 x 10(6) and 2 x 10(9) M-1 for Pseudomonas aeruginosa exotoxin A. Our results indicate that the detectability of antibody populations depends on the antigen concentrations in the solid phase and on the affinity distribution of the probe to be analyzed. In wells coated with high antigen concentrations, antibody titers reflected antibody concentrations, whereas at low antigen concentrations antibody titers primarily reflect antibody affinities. Independent of their affinities, subpopulations less than 10% could not be detected. Low affinity antibodies were preferentially underestimated. The degree of distortion depended on the composition of the probe to be analyzed. In general, the higher the absolute and the relative affinity of a population, the stronger was its capacity to interfere with the detection of other populations. As a consequence, the heterogeneity of affinity distributions in polyclonal samples may be substantially underestimated. The experiments reported provide guidelines for an optimal design and an adequate interpretation of ELISA based qualitative analyses of polyclonal antibody samples.

IgE-producing hybridomas established after B-cell culture in the CD40 system.

While total IgE synthesis can be easily induced in human PBL or B cells by different stimuli, no systems are known for the induction of allergen-specific IgE in vitro. In this study we investigated whether a specific Ig response could be induced using the CD40 culture system with the final intention to generate B-cell hybridomas secreting IgE of defined specificity. B cells derived from immunized donors normally give rise to many specific hybridomas after cell fusion. However, if cultured in the CD40 system and then immortalized and screened for anti-tetanus specificity, no tetanus-specific clones were found but a large number of IgE-secreting hybridomas had been generated. Also allergen-specific B cells could not be expanded in the CD40 system but long-term cultures yielded again B cells that were efficiently immortalized by cell fusion resulting in stable IgE-secreting hybridomas but of undefined specificity. One of these IgE-producing clones was further characterized and had an IgE production rate of 4.5 micrograms/10(6) cells/24 h. This paper provides two findings. (1) Our cell lines represent a valuable new source of human IgE. (2) Most importantly, our data indicate that the CD40 system is not suitable to expand specific B cells, suggesting that other systems have to be developed for the induction of a significant antigen-specific Ig response.

Feasibility of prophylaxis and therapy against gram-negative infections by human monoclonal antibodies.

In a murine model of Gram-negative sepsis, we have shown that the prophylactic application of human monoclonal antibodies (HmAbs) with specificity for lipopolysaccharides (LPS) of Pseudomonas aeruginosa protected against bacterial infection. In this paper we show that the therapeutical application of 5 micrograms of these HmAbs up to 6 h after challenge with a lethal dose of live P. aeruginosa results in a protection rate of 70-90%. Administration 18 h after bacterial challenge, diminished the protection to 43% survival rate. Furthermore, using a mixture of HmAbs recognizing a total of six different P. aeruginosa serotypes, no interference in their protective capacities was found. Finally, these HmAbs also protected galactosamine-sensitized mice against lethal challenge with LPS. Our data show that the described HmAbs confer bactericidal activity as well as anti-endotoxic activity in vivo.

Influence of somatic cell hybridization and human serum on the generation and stability of human hybridomas.

We describe an approach that allows the generation of stable hybridomas secreting antigen specific human IgG antibodies with an efficiency comparable to that of the generation of IgM and IgA secreting hybridomas. This was achieved by evaluating means to increase the frequency of human hybridoma formation and the stability of the generated hybridoma cells when subjected to conditions for large scale growth. To this end, we generated new fusion lines with an increased human DNA content and modified the culture system. However, the application of these new fusion lines primarily resulted in unstable giant cells. As a consequence, we evaluated whether the viability of newly formed hybrids between existing fusion lines and lymphoblastoid cell lines might be improved. In an attempt to provide as many components necessary for the growth of antibody secreting hybridomas as possible, we propagated fused cells in medium supplemented with human serum. Our results show that with this approach the frequency of initially growing hybrids was significantly increased. Furthermore, only in culture medium supplemented with human serum was it possible to obtain stable IgG secreting clones.

Optimization of growth and secretion of human monoclonal antibodies by hybridomas cultured in serum-free media.

To facilitate the production and purification of human monoclonal antibodies, we evaluated the ability of human hybridomas to adapt to chemically defined-serum free media. From a panel of human hybridomas secreting antibody against serotype specific lipopolysaccharide determinants of gram-negative bacteria, the growth and secretion properties of the two hybridomas producing antibodies against two strains of Pseudomonas aeruginosa, 4-8KH15 and 4-10KH139, were analysed. Both clones did not grow in protein-free medium. However, it was possible to adapt them to serum-free media consisting of a basal medium supplemented with insulin, transferrin, ethanolamine, and selenite. Antibody secretion rates were equal (4-8KH15: 26-31 micrograms IgM/10(6) cells/day) or higher (4-10KH139: 58-90 micrograms IgM/10(6) cells/day) in serum-free media as compared to conventional serum-supplemented medium. Our studies suggest that adaptation of the described hybridomas to selected serum-free media results in an antibody production which is very high as compared with reports in comparable systems. The establishment of these conditions will significantly facilitate the production of large amounts of human monoclonal antibodies which is a prerequisite for a therapeutical application.

Polyclonal preparations of anti-tetanus toxoid antibodies derived from a combinatorial library confer protection.

We have compared the in vivo therapeutic potential of anti-tetanus toxin (TT) human Fab antibodies derived from a combinatorial phage display library to established polyclonal and monoclonal reagents. The oligoclonality and fine specificity distribution of the synthetic anti-TT Fab preparations was comparable to the antibody spectrum present in the donor serum and the affinities determined for the synthetic phage-bound Fab (Phab) and soluble Fab were in the same range as their monoclonal and polyclonal counterparts. On a weight basis, the protective capacity of the new oligoclonal preparations in vivo (16.4 IU/100 micrograms Fab) was comparable to those of the best combinations of hybridoma derived human monoclonal antibodies, and far better than those exhibited by the polyclonal serum antibodies of the donor (0.29 IU/100 micrograms IgG) or by a standard commercial human tetanus immunoglobulin preparation. These data suggest that recombinant antibodies may become a safe and effective alternative to human plasma-derived immunoglobulins for passive immunization.

Cellular immunity in healthy volunteers treated with an octavalent conjugate Pseudomonas aeruginosa vaccine.

Humoral immunity in response to an octavalent O-polysaccharide-toxin A conjugate Pseudomonas aeruginosa vaccine is well studied, and a phase III clinical study in cystic fibrosis (CF) patients is currently ongoing. In contrast, little is known about cellular immunity induced by this vaccine. Fifteen healthy volunteers were immunized on days 1 and 60. Parameters of cellular immunity were studied before vaccination on day 1, and on day 74. Analyses included flow cytometry of whole blood and antigen-induced proliferation of and cytokine production by lymphocyte cultures. The effects of immunization on the composition of peripheral blood lymphocytes as determined by flow cytometry were minor. In contrast, after immunization a highly significant increase of proliferation in response to stimulation with detoxified toxin A was noted: the stimulation index rose from 1.4 on day 1 to 42.2 on day 74 (restimulation with 0.4 microg/ml; P = 0.003). Immunization led to significant production of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha by antigen-stimulated lymphocytes. In contrast, no significant induction of interleukin (IL)-4 or IL-10 was observed. In conclusion, immunization of healthy volunteers led to activation of cellular immunity including strong antigen-specific proliferation and cytokine production. In CF patients priming of the cellular immune system towards a Th1-like pattern would be of potential advantage. Therefore, confirmatory analyses in immunized CF patients with and without chronic infection with P. aeruginosa are foreseen.

Cellular immunity in healthy volunteers treated with an octavalent conjugate Pseudomonas aeruginosa vaccine.

Humoral immunity in response to an octavalent O-polysaccharide-toxin A conjugate Pseudomonas aeruginosa vaccine is well studied, and a Phase III clinical study in cystic fibrosis (CF) patients is currently ongoing. In contrast, little is known about cellular immunity induced by this vaccine. Fifteen healthy volunteers were immunized on days 1 and 60. Parameters of cellular immunity were studied before vaccination on day 1, and on day 74. Analyses included flow cytometry of whole blood, and antigen-induced proliferation of and cytokine production by lymphocyte cultures. The effects of immunization on the composition of peripheral blood lymphocytes as determined by flow cytometry were minor. In contrast, after immunization a highly significant increase of proliferation in response to stimulation with detoxified toxin A was noted: the stimulation index rose from 1.4 on day 1 to 42.2 on day 74 (restimulation with 0.4 microg/ml; P = 0.003). Immunization led to significant production of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha by antigen-stimulated lymphocytes. In contrast, no significant induction of interleukin (IL)-4 or IL-10 was observed. In conclusion, immunization of healthy volunteers led to activation of cellular immunity including strong antigen-specific proliferation and cytokine production. In CF patients priming of the cellular immune system towards a Th1-like pattern would be of potential advantage. Therefore, confirmatory analyses in immunized CF patients with and without chronic infection with P. aeruginosa are foreseen.

Affinities of endotoxin-specific human monoclonal antibodies, their polyclonal counterparts and murine monoclonal antibodies.

Affinity as a measurement of the strength of binding is a crucial factor in biological significance. In general, high-affinity antibodies are most effective in mediating immunological effector mechanisms. Here, we compare the affinity distributions of corresponding polyclonal and monoclonal human antibodies specific for lipopolysaccharide determinants of the nosocomial pathogen Pseudomonas aeruginosa. The affinities of the 14 human mAb analysed ranged from 8.3 x 10(5) to 7.5 x 10(8). The average affinities of their polyclonal counterparts, assessed by analysing chromatographically separated antibody populations, ranged from 1.7 x 10(6) to 6.3 x 10(7). Furthermore, the affinities of murine mAb of the same specificity ranged from 3.7 x 10(5) to 1.4 x 10(7). These results suggest that the generated human monoclonal anti-carbohydrate antibodies exhibit affinities comparable to or higher than those of their human polyclonal counterparts and those of murine mAb of the same specificity.

Localization of arginine kinase in muscles fibres of Drosophila melanogaster.

Arginine kinase (AK), a monomeric protein of mol. wt. 40 000, was purified from adult Drosophila melanogaster. Antiserum to AK was raised in rabbits; its specificity was established by immunodiffusion tests and by immunoreplicas of electropherograms. After electrophoresis in non-denaturing conditions, the immunoreactive material was shown to possess enzymatic activity. Localization of AK by indirect immunofluorescence on washed myofibrils showed that at least a fraction of the total cellular AK is bound to the contractile apparatus. In muscle fibres of third instar larvae and in isolated adult fibrillar flight muscle myofibrils, AK was localized within the Z-line region. Adult tubular muscle fibres (tergal depressor of the trochanter) showed fluorescence in the A-band. In all cases, the localization was independent of the state of contraction. Vertebrate B- and M-type creatine kinases have previously been localized at the Z-line and A-band (M-line) regions, respectively. Isoenzymic forms of AK have not been detected in Drosophila, however.

Monoclonal antibodies to human cytokeratins: application to various epithelial and mesothelial cells.

Immunohistological analysis of human tissue using monoclonal antibodies against cytokeratins, which are confined to cells of epithelial origin, is a valuable technique. Using human epidermal keratins as antigen, we prepared monoclonal antibodies against cytokeratins (ZK1, ZK7, ZK61 and ZK99) and against a desmosomal protein (ZK31). Immunohistochemical staining of human skin sections using these antibodies showed a specific reaction with the epidermis: ZK1 stained the entire epidermis, ZK7 only the basal layer, ZK61 and ZK99 the suprabasal layers, and ZK31 the cellular interfaces. In order to test for antibody specificity, immunoblots with human epidermal and amnion epithelial cytokeratin polypeptides, as well as immunofluorescence microscopy of simple epithelia (glandular and simple columnar epithelia) were performed. ZK1, ZK61 and ZK99 reacted preferentially with cytokeratin polypeptides of stratified squamous epithelia and ZK7 recognized cytokeratins of stratified and simple epithelia. When the ZK antibodies were tested on mesothelial cells in pleural effusions, only ZK7 reacted with these cells. Biochemical analysis of cytokeratin accumulation in cells of primary and long-term cultures indicated that the cytokeratin pattern of mesothelial cells was quite unstable, while that of amnion epithelial cells showed only minor quantitative changes. The use of these antibodies to determine the epithelial origin of cells present in pleural effusions is proposed.

Scale-up and optimization of culture conditions of a human heterohybridoma producing serotype-specific antibodies to Pseudomonas aeruginosa.

Three different stirred bioreactors of 0.5 to 121 volume were used to scale up the production of a human monoclonal antibody. Inoculation density and stirrer speed were evaluated in batch cultures, whereas dilution rate and pH were optimized in chemostat cultures with respect to high specific antibody production rate and high antibody yield per time and reactor volume. The cell line used for the experiments was a heterohybridoma, producing immunoglobulin M (IgM) against lipopolysaccharide of Pseudomonas aeruginosa. Cells were cultured in spinner flasks of 500 ml liquid volume for adaptation to stirred culture conditions. Subsequently cells were transferred to the 1.5-l KLF 2000 bioreactor and to the 12-l NLF 22 bioreactor for pilot-scale cultures. Chemostat experiments were done in the 1.5-l KLF bioreactor. Cell density, viability, glucose and lactate and antibody concentration were measured during culture experiments. In batch cultures in all three stirred bioreactors, comparable maximal cell densities and specific growth rates were achieved. Chemostat experiments showed that at a pH of 6.9 and a dilution rate of 0.57 per day the specific antibody production rate was threefold higher than similar experiments done at pH 7.2 with a dilution rate of 0.36 per day. By optimizing pH and dilution rate in chemostat cultures the daily yield of human IgM increased nearly threefold from 6 to 16 mg/day and per litre of reactor volume. The yield per litre of medium increased twofold.

Protein transport across the in vitro perfused human placenta.

PROBLEM: Placental transport of various proteins present in human serum, such as immunoglobulins (IgG, IgA), specific anti-tetanus IgG (anti-TT-IgG), and tetanus toxoid-antigen (TT-AG), was investigated. In addition, the transport of IgG modified with biotin (IgG-BT) and 14C-bovine serum albumin (14C-BSA, a permeability marker for macromolecules), was assessed. METHOD OF STUDY: During the perfusion of an isolated cotyledon from human term placenta the perfusate was recirculated on both maternal and fetal sides. After an initial stabilisation phase of 2 hr (control phase), media on both sides were exchanged and perfusion was continued comparing two different conditions (experimental phase). In the first group (control experiments [A, n = 3]), no test proteins were added during the experimental phase (4-6 hr). In the second group (B, n = 5), during the experimental phase (6 hr) the maternal perfusion medium contained IgG (Sandoglobuline, 6-10 g/L), anti-TT-IgG (21-25 mg/L), TT-AG (0.19-0.24 mg/L), and IgA (0.13-0.19 g/L). IgG-BT (2 g/L) and 14C-BSA (30-40 nCi/ml) were added to the medium on the maternal side. IgGs and TT-AG were determined by specific enzyme-linked immunosorbent assay. RESULTS: Both groups showed stable metabolic conditions with constant rates of glucose consumption, lactate production, and hormone (human chorionic gonadotropin, human placental lactogen) release observed throughout the experiment. Washout levels of endogenous IgG and IgA observed in the maternal circuit at the end of the control period were 5 and 1000 times higher than in the fetal circuit. In the experimental phase these levels remained constant at 50-80% of control levels with no change in the last 4 hr of perfusion (group A). In group B, with addition of extra proteins, trace amounts of IgG-BT, IgA, and 14C-BSA were detectable in the fetal circuit within 1 hr, with no significant further increase in circulating levels in the following 4 hr of the perfusion. In contrast, the detection of IgGs in the fetal circuit was delayed by 2 hr; thereafter, a continuous linear increase was observed for all IgGs. TT-AG in fetal perfusate was below the detection limit. TT-AG was found on the fetal side only after ultrafiltration of samples obtained at the end of the experiment. For permeability comparison, the ratio between concentrations on the fetal and maternal side multiplied by 100 ([F:M] x 100), as detected after 6 hr of perfusion, was assessed (n = 5, mean +/- SD). Labelling of IgG with biotin (IgG-BT) reduced its placental transfer by a factor 10 (0.04 +/- 0.01) when compared with the natural IgG (0.49 +/- 0.08) or the specific antibody (anti-TT-IgG). The relative fetal-to-maternal ratio found for TT-AG (0.48 +/- 0.12) was similar to anti-TT-IgG (0.46 +/- 0.11), and approximately 4 and 50 times that of 14C-BSA (0.12 +/- 0.03) and IgA (0.01 +/- 0.01), respectively. Considering that the molecular weights of TT-AG and anti-TT-IgG were at least twice that of BSA and similar to IgA, the difference in transfer suggests a specific mechanism of transport. CONCLUSIONS: Compared with other proteins there is a significantly increased transfer of IgGs across the in vitro perfused human placenta from the maternal to the fetal side, indicating a specific transport mechanism. The similarity in transfer of anti-TT-IgG and tetanus antigen may suggest the transport as antibody-antigen complex.

Monoclonal antibodies that define neutralizing epitopes of pertussis toxin: conformational dependence and epitope mapping.

The epitope specificities of 13 hybridomas secreting monoclonal antibodies (MAbs) specific for pertussis toxin (PT) is described. Hybridoma lines were derived by the fusion of spleen cells from mice immunized with native PT, Formalin-detoxified PT, or isolated PT subunits (S1 to S5) with the myeloma line X63-Ag8.653. Five MAbs showed a toxin-neutralizing ability, which was demonstrated by use of a Chinese hamster ovary cell assay system and by a NAD glycohydrolase assay. All five toxin-neutralizing MAbs demonstrated high specificities for and reactivities with native PT but were unable to bind to denatured PT. One MAb was able to neutralize the enzymatic activity of PT. The other four neutralizing MAbs inhibited the binding of PT or PT subunits to the surface of Chinese hamster ovary cells, as shown by an immunofluorescence assay. All neutralizing MAbs reacted with purified S2-S4 or S3-S4 dimers but not with S4 alone. Three MAbs which recognized a common epitope shared by S2 and S3 (which are about 70% homologous at the DNA level) and one MAb which recognized S4 were not neutralizing. Isolated S2-S4 and S3-S4 dimers bound to Chinese hamster ovary cells. These results indicate that the majority of critical epitopes which elicit neutralizing antibody are conformation dependent.

Characterization of the Shigella serotype D (S. sonnei) O polysaccharide and the enterobacterial R1 lipopolysaccharide core by use of mouse monoclonal antibodies.

In the course of developing a live vaccine, we generated three murine monoclonal antibodies (MAb) specific for Shigella sonnei. The specificities of these MAb were determined by enzyme-linked immunosorbent assay and immunoblot analyses with whole cells or purified lipopolysaccharides (LPSs) as antigens. Two of them are specific for the Shigella serotype D O-polysaccharide determinant, whereas one specifically binds to the core hexose region of R1-type LPSs. With these MAb, it was possible to analyze clinical isolates and a hybrid Salmonella typhi strain for their expression of the corresponding LPS moieties. In addition to their use in the screening of candidate vaccine strains, the new MAb provide a powerful tool for epidemiological and phylogenetic studies of natural enterobacterial populations.