Optimal conditions for polyclonal antibody secretion and DNA synthesis in human blood and spleen lymphocytes by lipopolysaccharide

Mitogenic activation of human lymphocytes: a protein A plaque assay evaluation of polyclonal B-cell activators

Using the protein A plaque assay, the capacity of various polyclonal B cell activators to induce differentiation in human B lymphocytes was investigated. Dextran sulphate and native dextran were both virtually devoid of mitogenic properties. Lipopolysaccharide, however, was found to be a potent mitogen in human cells that, although giving rise to low DNA synthetic response, induced high numbers of immunoglobulin-synthesizing cells. Mean plaque-forming cell (PFC) numbers in healthy blood donors assayed on the optimal day (days 5-7) were 23,493 IgM/10(6) cells, 11,288 IgG/10(6) cells, and 2643 IgA/10(6) cells. Values obtained in spleen cells, peaking at days 4-6, were slightly higher. Purified protein derivative (PPD) was equally or even more effective than lipopolysaccharide (LPS) in generating PFC of different subclasses in peripheral blood with mean of 29,241 IgM/10(6), 21,269 IgG/10(6), and 3681 IgA/10(6). PPD furthermore induced a marked DNA synthetic response in human lymphocytes. These data suggest that LPS and PPD may both be used as functional markers in human cells when analysing patients with a suspected immunodeficiency state. It is suggested that cultures should be assayed using the protein A plaque assay, thereby being able not only to investigate the individual immunoglobulin classes but also to avoid the possible hazards involved in measuring antigen-specific responses in patients whose prior immunization to the antigen tested can never be totally excluded.

Antibody secretion and DNA synthesis induced by lipopolysaccharide in enriched human lymphocyte subpopulations

Lipopolysaccharide (LPS)-induced human lymphocyte activation was analysed with regard to DNA synthesis and antibody secretion. Antibody secretion was measured as plaque-forming cells (PFC) against fluorescein isothiocyanate (FITC)-coupled sheep erythrocytes (SRBC) or protein-A-coupled SRBC in the presence of developing antiserum against human IgG, IgA and IgM subclasses. By co-culturing lymphocytes with various concentrations of mitomycin, without impairing cell viability, inhibition of DNA synthesis and antibody secretion by LPS was correlated. Antibody secretion against FITC-SRBC or protein A-SRBC was not stimulated by LPS in B cells enriched by elimination of SRBC rosette-forming cells (E-RFC). In mixtures of enriched T and B cells the number of PFC was much lower than in unseparated lymphocytes, but the highest number of PFC was seen in the enriched E-RFC. However, DNA synthesis by LPS was induced in enriched B cells and not in enriched T cells. The highest DNA synthesis was seen for unseparated lymphocytes. Furthermore, autoradiography studies and experiments in which activated lymphocytes were separated revealed that LPS predominantly stimulated DNA synthesis in non-E-RFC, presumably B cells and only activated a small proportion of E-RFC. Finally, antibody secretion induced by LPS was unchanged following iron treatment but was inhibited by cells adherent to plastic.

Study of the immunostimulating effect of IM-104 in mice

The results of this study show that the product IM-104 has a marked immunostimulant effect, when administered intraperitoneally in mice, as seen by the increase in the number of haemolytic plaque-forming cells producing antibodies against sheep erythrocytes, as compared with saline-treated controls.

Expression and characterization of a B cell growth promoting polypeptide derived from the 12 kDa B cell growth factor gene (BCGF 1)

The expression and partial purification of recombinant 12 kDa B cell growth factor are reported. The polypeptide was derived from the genomic sequence of the gene (BCGF 1) which is here shown to be a single copy gene that localizes to human chromosome 16. When expressed as a glutathione S-transferase fusion protein in E. coli, the protein appears as a 38 kDa polypeptide in Western blot analysis using a peptide antibody. The purified fusion protein stimulates the proliferation of activated human B cells in a dose-dependent manner, and the active site resides within the 104 carboxy-terminal amino acids. The availability of biologically active recombinant 12 kDa B cell growth factor will enable its evaluation in B cell growth regulation, and provides a new means of in vitro culturing of human B lymphocytes.

Bacteria are polyclonal T-dependent stimulants of immunoglobulin formation

Various gram-positive and gram-negative bacteria were tested for their ability to induce antibody secretion in human blood cell cultures. Total and specific immunoglobulin levels in the culture supernatants were quantitated with enzyme-linked immunosorbent assays (ELISA). All the twelve strains used stimulated IgM and IgG secretion in adult mononuclear cell cultures. With the four strains tested, also umbilical cord blood cells produced IgM. Specific antibodies directed against two bacteria were sought in adult and newborn cell culture but none were found. Bacterium-induced antibody synthesis thus seemed to be polyclonal. Experiments with purified T and B lymphocytes showed that bacterium-driven antibody formation was T-cell dependent.

Stimulation of human blood lymphocyte by different polyclonal B cell activators of bacterial and plant origin: production of IgM, IgG and IgA estimated by the ELISA method

Lymphocytes isolated from peripheral blood of healthy donors were stimulated in vitro with pokeweed mitogen, concanavalin A, flagellin, Nocardia delipidated cell mitogen (NDCM) and heat-killed bacteria Escherichia coli and Actinomyces viscosus. A simple and sensitive technique, enzyme-linked immunosorbent assay (ELISA) was used for the detection of nanogram levels of IgM, IgA and IgC in media from lymphocyte cultures after polyclonal stimulation, Pokeweed mitogen, NDCM and E. coli were shown to stimulate a high production of IgM; after stimulation with A. viscosus a higher production of IgA was detected. No immunoglobulin production was observed after stimulation with polymerized flagellin.

Effect of bacterial lipopolysaccharide on bovine polymorphonuclear neutrophil migration in vitro

The in vitro effects of Escherichia coli 026:B6 lipopolysaccharide (LPS) on random migration of bovine polymorphonuclear neutrophils (PMN) was investigated. Treatment of peripheral blood leukocytes (PBL) with LPS significantly inhibited PMN migration. These inhibitions were observed at a threshold concentration of 5.0 micrograms/2.0 X 10(6) PBL. PMN migration inhibition was eliminated in PBL by the addition of polymyxin B, which binds the Lipid A moiety of LPS. Treatment of isolated PMNs with LPS significantly enhanced migration. Enhanced migrations were observed at threshold concentration of 2.5 micrograms/4.0 X 10(6) PMN. Collectively these findings indicate that the inhibition was caused by leukocyte inhibitory factor (LIF) production in PBL cultures, whereas enhancement was probably caused by PMN activation. These results provide further insight into the effects of LPS on in vitro bovine PMN migration by its distinct actions on different cells of PBL.

Interleukin 1 secretion by human monocytes stimulated by the isolated polysaccharide region of the Bordetella pertussis endotoxin

The isolated polysaccharide chain, PS-1, of the Bordetella pertussis endotoxin was examined by isoelectric focusing, SDS-polyacrylamide gel electrophoresis and gel filtration for heterogeneity and for possible contamination by the parent endotoxin. This polysaccharide, previously found to be a very potent, macrophage-dependent, polyclonal B-cell activator and to mediate the specific binding of the endotoxin to macrophages, stimulated the interleukin 1 (IL 1) secretion by human monocytes; its potency was similar to that measured for the endotoxin. It was concluded that endotoxin-induced IL 1 production may be initiated by the interaction of the polysaccharide chain of the B. pertussis endotoxin and a specific structure present on macrophages.

Chlamydia trachomatis stimulates human peripheral blood B lymphocytes to proliferate and secrete polyclonal immunoglobulins in vitro

Infectious Chlamydia trachomatis (LGV strain), obligate intracellular bacteria, stimulated human peripheral blood lymphocytes to proliferate and secrete immunoglobulins in vitro. In contrast, mock-infected preparations were unable to induce similar responses in peripheral blood lymphocytes. Although levels of immunoglobulin secreted into the media of LGV-stimulated cultures were greater than 10 micrograms/ml, we estimated that less than 1% of these molecules were directed against the bacteria itself, suggesting polyclonal antibody production. Since stimulation with Formalin-killed bacteria resulted in comparable numbers of plaque-forming cells (PFC) as infectious particles, we concluded that the polyclonal immunoglobulin response was not dependent on the in vitro chlamydial infectious process. The polyclonal PFC response induced by LGV was highly sensitive to monocyte inhibition. Although LGV induced proliferation of predominantly B cells, the numbers of generated PFC was increased by the addition of autologous T cells. Neither lymphocyte proliferation nor PFC responses of normal human volunteers correlated significantly with the presence or titer of antichlamydial antibodies in their sera.

Human rheumatoid factor-producing cell induction by 2-mercaptoethanol: immunomodulation by a simple thiol compound

Two-mercaptoethanol (2-ME), a simple 2 carbon thiol compound with a wide variety of in vitro and in vivo immunomodulating effects, was evaluated for its usefulness as a molecular probe of human antibody producing cell activation by adding 2-ME to cultures of peripheral blood mononuclear leukocytes from normal human volunteers. Culturing normal human leukocytes with 2-ME induced a significant number of cells producing rheumatoid factor as measured by a hemolytic plaque forming cell (PFC) assay. Dose response studies revealed 5 X 10(-5)M to be the optimum concentration of 2-ME for the induction of rheumatoid factor plaque forming cells (RF-PFC). This concentration of 2-ME also maximally induced PFC making antibodies to sheep red cells coupled to the trinitrophenyl (TNP) hapten demonstrating that 2-ME is a polyclonal inducer of human PFC. The addition of 5 X 10(-5) M 2-ME to cultures containing maximal concentrations of the polyclonal stimulators, pokeweed mitogen and human heat-aggregrated IgG, increased the number of RF-PFC detected in these cultures by approximately 50%, although both lower and higher concentrations of 2-ME suppressed the RF-PFC response. We conclude that 2-ME induces normal human leukocytes to produce rheumatoid factor as part of a polyclonal activation of antibody producing cells. 2-ME also has immunomodulating effects when added to other polyclonal stimulators of antibody producing cells.

Menningococcal antigens (MA): a novel immune stimulant in experimental neoplasia

An extract of the meningococcus antigens (MA) prepared from N. meningitidis was tested for an anti-tumor effect in rat and murine metastasizing tumor models. Effectiveness of MA in each model varied with dose and was manifested as significantly improved survival of the treated animals. Growth of the primary Fischer bladder carcinoma (FBCa) and metastases to lungs and lymph nodes were significantly inhibited in F344 rats treated weekly with 1 mg MA. Administration of MA at 100 micrograms per animal significantly prolonged survival of P815 mastocytoma-inoculated DBA/2 mice. Survival of C-26 colon adenocarcinoma-bearing Balb/c mice was significantly improved in animals that received weekly injections of 20 micrograms MA, without significant effect on the development of local tumor. The meningococcal antigens demonstrate strong mitogenic activity in B-cell-enriched murine spleen cultures. Thus the immunostimulatory activity of MA in experimental malignancy could involve, directly or indirectly, activation of B lymphocytes.

Studies on the mechanism of peptidoglycan- and lipopolysaccharide-induced polyclonal activation

Peptidoglycan (PG) and lipopolysaccharide (LPS) are T cell-independent B cell mitogens and polyclonal activators in mice. The mechanism of in vitro proliferation and polyclonal activation of mouse splenocytes induced by PG from Staphylococcus aureus and LPS from Escherichia coli was further studied by using [3H]thymidine incorporation and protein A hemolytic plaque assays. Concanavalin A-generated suppressor cells suppressed both polyclonal and proliferative responses induced by PG, LPS, and pokeweed mitogen. The suppression of the proliferative responses was similar for all these mitogens, but was significantly less pronounced than the suppression of the polyclonal antibody response. Polyclonal activation induced by LPS was the most susceptible to suppression by concanavalin A-generated suppressor cells, and the suppression was significantly greater than in the PG-induced polyclonal response. Also, PG-induced polyclonal activation was not susceptible to inhibition by polymyxin B, which is an inhibitor of other B cell mitogens and polyclonal activators. For optimal generation of immunoglobulin-secreting cells, PG of LPS had to be present for at least 48 h after the initiation of the cultures. Removal of the mitogens after 4 or 24 h of incubation resulted in a suboptimal response. For effective induction of the proliferative response, the mitogens had to be present in cultures for over 24 h. Polyclonal-activating properties of staphylococcal cell wall components were also compared. PG was by far the most potent inducer of polyclonal antibodies. Teichoic acid was not active as a polyclonal activator, whereas purified cell wall and protein A were very weak inducers of polyclonal antibodies. These studies demonstrate that PG, in addition to LPS, can be a useful probe for studies on polyclonal activation.

Activation of human peripheral blood lymphocytes: effect of concanavalin A and lipopolysaccharide on in vitro synthesis of DNA and immunoglobulins

We studied the interaction of lipopolysaccharide (LPS) and concanavalin A (Con A) with regard to IgM and IgG production in in vitro cultures of human peripheral blood lymphocytes (PBL). In our system LPS alone over a wide range of concentrations did not stimulate detectable IgM or IgG production, while Con A at optimal (6 microgram/ml) and suboptimal (0.6 microgram/ml) mitogenic concentrations induced synthesis of small amounts of Ig. A marked enhancing effect was present when both Con A and LPS were added to the cultures. The different doses of LPS has similar effects on both classes of Ig, and typical dose-response curves were obtained. To evaluate the cellular basis of this synergism, the effect on cell proliferation was studied under identical experimental conditions in normal subjects and patients with X-linked agammaglobulinaemia (X-LA). Parallel cultures were set up after monocyte depletion by adherence on Petri dishes. On day 3, increasing doses of LPS were associated with progressive decreases in 3H-thymidine (3H-TdR) incorporation. Similar results were obtained with normal lymphocytes and those from X-LA patients. Monocyte depletion did not substantially alter the lymphocyte response pattern. The preferential induction of helper activities, either directly by helper stimulation or indirectly by suppressor inhibition, is suggested as a possible mechanism of the interaction observed.

Polyclonal antibody secretion induced in human mixed lymphocyte cultures. II. No direct activation of B cells

Antibody secreting B cells were measured as plaque forming cells (PFC) in a hemolysis-in-gel assay using fluorescein isothiocyanate (FITC) coupled SRBC as targets or protein A coupled SRBC as targets and developing antisera. Peak antibody secretion occurred on day 5 and the highest number of PFC was seen when mitomycin treated stimulator cells: responder cells were used in a ratio of 1:4. The number of PFC in MLC was not correlated to the DNA synthetic response. Antibody secretion in MLC was found to be of IgM, IgG and IgA classes. Significant numbers of PFC in MLC from blood lymphocytes were detected with the protein A technique, but not using FITC-SRBC targets. Compared to spleen cells, fewer PFC were stimulated in blood lymphocytes. B cells alone, enriched by rosetting of T cells, did not respond by antibody secretion or DNA synthesis in MLC. When Lipopolysaccharide (LPS) was added to MLC an additional effect was seen on the number of PFC which may indicate that distinct B cell subpopulations are activated in MLC by LPS.

Lipopolysaccharide and lipid A-induced human blood lymphocyte activation as detected by a protein A plaque assay

Various purified cell wall lipopolysaccharides (LPS) from gram-negative bacteria and derivatives of these LPS were tested for their stimulatory capacity for human peripheral blood cells. Immunoglobulin (Ig) production was tested by an indirect plaque-forming cell assay using Staphylococcus aureus protein A-coupled erythrocytes and specific anti-Ig as developing serum. This method allows the detection of the majority of cells secreting Ig of a single class, and the number of plaque-forming cells detected are approximately 100-1000 times the amount obtained using normal sheep red cells as targets. LPS containing the O antigen-specific chain, as well as mutant products only containing lipid A and ketodeoxyoctonate trisaccharide, could induce cell division and antibody synthesis. The polypeptide antibiotic polymyxin B was found to inhibit LPS-induced activation. Furthermore, purified lipid A, complexed with bovine serum albumin, was also found to activate human peripheral blood B cells. These findings demonstrate that human peripheral blood lymphocytes can be activated by LPS and also indicate that lipid A is the active part of these molecules.