Activation of human B lymphocytes. I. Direct plaque-forming cell assay for the measurement of polyclonal activation and antigenic stimulation of human B lymphocytes

Immunotoxicology: Opportunities for Non-animal Test Development

At present, several animal-based assays are used to assess immunotoxic effects such as immunosuppression and sensitisation. The use of whole animals, however, presents several secondary issues, including expense, ethical concerns and relevance to human risk assessment. There is a growing belief that non-animal approaches can eliminate these issues without impairing human safety, provided that biological markers are available to identify the immunotoxic potentials of new chemicals to which humans may be exposed. Driven by the 7th Amendment to the EU Cosmetics Directive, the new EU policy on chemicals (the REACH system), proposals to update the European legislation on the protection of animals used in research, and emerging visions and strategies for predicting toxicity, such in vitro methods are likely to play a major role in the near future. The realisation that the immune system can be the target of many chemicals, resulting in a range of adverse effects on the host's health, has raised serious concerns from the public and within the regulatory agencies. Hypersensitivity and immunosuppression are considered the primary focus for developing in vitro methods in immunotoxicology. However, in vitro assays to detect immunostimulation and autoimmunity are also needed. This review of the state-of-the-art in the field of in vitro immunotoxicity, reveals a lack of cell-based immunotoxicity assays for predicting the toxicity of xenobiotics toward the immune system in a simple, fast, economical and reliable way.

Activation of human lymphocyte subpopulations by Mycoplasma pneumoniae

B- and T-cell-enriched preparations of lymphocytes from human blood (5 cases), adenoids (10 cases), and tonsils (4 cases) were examined for the in vitro stimulation response to Mycoplasma pneumoniae (MP). B lymphocytes did not respond to MP by DNA synthesis except for the B cells from one adenoid. T lymphocytes and nonfractionated lymphocytes from blood, from three of the adenoids and two of the tonsils showed a stimulation response to MP. Nonfractionated adenoid lymphocytes from altogether 22 children were examined, and a stimulation response to MP was demonstrated in 8 cases. Lymphocyte cultures from 11 adenoids and 2 tonsils were examined for MP-induced non-antigen-specific antibody production by a hemolytic plaque assay. In all these cultures MP activated production of antibody-secreting cells to sheep erythrocytes. It is concluded that MP can induce non-antigen-specific angibody production in human B lymphocytes without stimulating DNA synthesis in these cells. The proliferative response of adenoid, tonsil, and blood lymphocytes to MP is interpreted as an antigen-specific T-cell response.

Spontaneous plaque-forming human lymphocytes detected with the protein-A plaque assay

A sizable proportion of fresh human blood and adenoid lymphocytes were found to produce antibodies when tested in the protein-A plaque assay of Gronowicz et al. Plaque formation was not caused by release of passively adsorbed immunoglobulin but depended on active immunoglobulin secretion. We have investigated optimal conditions for plaque formation in this test system. Good reproducibility is obtained only if cells to be tested are kept in the cold before assay, since the antibody-forming capacity of these cells is rapidly exhausted at temperatures above 2 degrees C. In blood lymphocytes the number of IgA-producing cells exceeds those of IgG and IgM, whereas in the adenoid IgG plaque-forming cells dominate. Studies on the use of this method for the monitoring of immune responses are in progress.

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.

The effects of CP 17193, an immunosuppressive pyrazaloquinoline, on the development of spontaneous lupus disease in NZBW F1 hybrid mice

The effects of the immunosuppressive agent CP 17193 on the development of spontaneous lupus disease in female NZBW F1 hybrid mice were investigated. Long term dosing with CP 17193 markedly delayed the onset of mortality but did not extend the long term survival of the mice. CP 17193 significantly inhibited immune complex deposition in the glomeruli of 30- and 35-week-old mice and also reduced the levels of proteinuria in the 35-week-old mice. There was a slight reduction in the levels of circulating antinuclear antibody to ds DNA in CP 17193-treated mice but this was not statistically significant. Studies on immune cell function of 35-week-old mice dosed with CP 17193 showed significant reduction in the total numbers of spontaneous polyclonal antibody producing cells. Analysis of the results revealed these effects to result from a marked reduction in total spleen cell numbers in CP 17193-treated mice. When results were expressed as activity per cell unit the differences between drug-treated and control mice were small. Spleen cells from mice given a shorter dosing schedule of 7 weeks with CP 17193 showed an augmentation of IL-2 production and responsiveness. These results show CP 17193 having interesting selective immunomodulating activity on the immunopathogenesis of spontaneous murine lupus disease. Furthermore, compounds with this profile of activity may have a potential role in the treatment of some autoimmune diseases.

Antigen-specific plaques formation of cultured mononuclear cells in head and neck cancer

Antigen-specific antibody production in vitro from peripheral blood mononuclear cells was studied for the assessment of the immune competence of patients with head and neck cancer. Optimal culture conditions were studied using inactivated Staphylococcus aureus and a saturation with IL-1 during B cell activation and pooled human AB serum on day 2. After passage of the mononuclear cells through sephadex G-10 columns, a significant increase in the antigen-specific antibody production was observed. In healthy donors a significant reduction of the antigen-specific antibody production according to the abuse of alcohol and/or cigarette smoking was detectable. Interestingly, high alcohol consumption resulted in a more pronounced decrease of the antigen-specific antibody production in vitro than excessive cigarette smoking. Patients with squamous cell carcinoma of the head and neck who are considered to be most immunodeficient did not show any antigen-specific antibody production in vitro upon activation with sheep red blood cells in the presence of Interleukin-1 (IL-1). After filtration of mononuclear cells from peripheral bloodover sephadex G-10 beads, two thirds of the patients studied became stimulable. This increase in the antigen-specific antibody production in vitro was significant, though not as dramatic as in the age- and sex-matched control groups. Interestingly, the antigen-specific antibody production raised almost to the same level as that measured in healthy donors with high alcohol abuse and cigarette consumption.

Immunosuppressive effects of dietary wortmannin on rats and mice

In order to assess the effects of the fungal toxin wortmannin on the immune system, rats and mice were fed wortmannin-containing cultures of Fusarium oxysporum for 1 or 2 weeks. Wortmannin caused significant decreases in thymic weight, thymic lymphocyte numbers, serum IgG and IgM levels, the primary humoral response to T-dependent and T-independent antigens and the proliferative response of spleen cells to pokeweed mitogen. In vitro administration of wortmannin did not produce evidence of cytotoxicity to spleen or thymus cells. The data indicate that wortmannin inhibits immune function in rats and mice and suggest that metabolic modification of the toxin is necessary for toxicity.

Immunoglobulin secretion of mononuclear cells induced by various mitogens

Immunosufficiency can be evaluated by Ig secretion subsequent to mitogenic stimulation of human mononuclear cells (MNC). It seems that there are significant differences in immunoglobulin class secreted by these cells when stimulated with various polyclonal activators. The aim of the current study was to analyse these differences. MNC cells was randomly obtained from nine healthy blood donors and were activated by Epstein-Barr virus (EBV), group-A streptococcus (A-ScM), Staphylococcus aureus (SAC), Klebsiella pneumonia (Kleb-M) and pokeweed mitogen (PWM). Significantly increased levels of IgM were recorded after a 7 day incubation followed by stimulation with Kleb-M (6.2 +/- 2.9) and EBV (5.9 +/- 4.5) compared to inactivated MNC (1.6 +/- 1.4), and following 10 days incubation then stimulation by EBV (13.4 +/- 5.5) and Kleb-M (9.9 +/- 4.2) compared to unstimulated cells (2.9 +/- 1.8). Significantly greater IgG levels were achieved following incubation with EBV (3.0 +/- 4.0) and PWM (2.4 +/- 1.3) after 7 days (vs 0.6 +/- 0.4 in unstimulated cells) and by PWM (11.7 +/- 5.3) and Kleb-M (8.8 +/- 3.9, vs 2.3 +/- 2.2) after 10 days. The present data emphasize the significance of merging both mitogen selection and culture duration for acquiring information and high fidelity results of immunoglobulin secretion by polyclonal activators.

Polyclonal antibody secretion during acute graft-versus-host disease

Spontaneous plaque-forming cells (S-PFC) were followed in 67 bone marrow transplantation (BMT) recipients and 41 controls. Patients with no acute graft-versus-host disease (GVHD) had decreased IgA and IgM S-PFC up to 7 weeks after BMT compared with controls. Patients with acute GVHD had increased IgG, IgA, and IgM PFC compared with controls and patients without GVHD during the first 4 weeks after BMT. The maximum number of S-PFC increased with increasing severity of acute GVHD. However, at diagnosis of GVHD there was no difference in S-PFC in patients who resolved their GVHD or in those who developed more severe GVHD. After 6 weeks, patients with acute GVHD had significantly decreased IgA and IgM S-PFC compared with normal. No major changes in S-PFC were induced during various infections. However, a patient who developed urticaria had a dramatic increase in S-PFC. Patients studied more than a year after BMT had reduced IgM S-PFC compared with controls. It is concluded that S-PFC are reduced after BMT, but markedly enhanced during acute GVHD.

Electrophoretic separation of cells

There are several kinds of cell electrophoresis. The most important are free-flow electrophoresis, scaled-up free-flow electrophoresis and column electrophoresis. All kinds of cell electrophoresis, especially free-flow electrophoresis, have been improved to a very high standard of separation accuracy, and their application possibilities are extended when antigen-specific electrophoretic cell separation is performed, or when cell electrophoresis is combined with other physical methods for cell separation. Cell electrophoresis and other physical cell separation methods have the advantage that the functional state of the cells remains virtually unchanged during the isolation procedure. With the help of cell electrophoresis monocytes, T-lymphocytes, platelets and other cells from human peripheral blood could be purified. Other human cells were enriched for immunological characterization. Furthermore, cells that secreted human plasminogen activators or human antibodies were electrophoresed to give cell fractions with increased frequencies of the cells of interest.

Limiting dilution analysis of specific in vitro anti-herpes simplex virus antibody production by human lymphocytes

An enzyme linked immunosorbent assay (ELISA) system to study specific anti-herpes simplex virus (HSV) antibody production in vitro by human peripheral blood mononuclear cells (PBMC) has been developed. HSV specific antibody production was detected in culture supernatants of PBMC from HSV seropositive healthy individuals by stimulating with optimal concentrations of HSV antigen without mitogens. To investigate the specificity of the resulting antibody, a limiting dilution analysis was performed as follows. PBMC from HSV-1 seropositive and HSV-2 seronegative individuals were stimulated by wild type HSV-1 (KOS), glycoprotein C deletion mutant of HSV-1 (MP), and wild type HSV-2 (186), and the precursor frequencies of B cells which produce antibodies to HSV-1 (KOS), HSV-1 (MP) and HSV-2 (186) were then estimated. When PBMC from five individuals were stimulated by HSV-1 (KOS), the estimated precursor frequencies of B cells which produced antibodies to HSV-1 (KOS), HSV-1 (MP), and HSV-2 (186) were 1/79,000 to 1/37,000, 1/104,000 to 1/52,000. and 1/78,000 to 1/101,000, respectively. On the other hand, when PBMC were stimulated by HSV-1 (MP) and HSV-2 (186), the precursor frequencies of B cells which produced antibody to HSV-1 (KOS) were the same as those to HSV-1 (MP) and HSV-2 (186), respectively. By using the experimental systems reported here, it became possible to determine clearly the immune status to HSV type-specific and type-common antigens and to each viral glycoprotein.

Suppressive effect on polyclonal B-cell activation of a synthetic peptide homologous to a transmembrane component of oncogenic retroviruses

Purified feline leukemia virus, UV light-inactivated feline leukemia virus, and a synthetic peptide (CKS-17) homologous to a well-conserved region of the transmembrane components of several human and animal retroviruses were each studied for their effects on IgG production by feline peripheral blood lymphocytes. Using a reverse hemolytic plaque assay, both the viable virus and the UV-inactivated feline leukemia virus, but not the CKS-17, activated B lymphocytes to secrete IgG. When staphylococcal protein A, a polyclonal B-cell activator, was used to stimulate IgG synthesis by feline lymphocytes, the viable virus, the UV-inactivated virus, and the CKS-17 peptide each strongly suppressed IgG secretion without compromising viability of the lymphocytes. These findings suggest that the immunosuppressive influences of feline leukemia virus on immunoglobulin synthesis may reside in a conserved portion of the envelope glycoprotein that includes the region homologous to CKS-17.

Orally induced tolerance to casein in mice on normal mouse chow

We examined the ability of bovine casein to induce oral tolerance in BDF1 mice raised on a normal mouse chow diet. Giving 20 mg casein 1 X or 4 X by intragastric tube or for 28 days at 1 mg/ml in drinking water failed to have a significant effect (P greater than 0.2) on the subsequent immune response to parenteral casein, suggesting that casein was not an effective oral tolerogen. However, we discovered that most normal mouse chow contains casein. When BDF1 mice were raised on a casein-free diet, and treated as above, they showed marked suppression of subsequent responses to parenteral casein (P less than 0.01). Our results indicated that mice on the normal diet were presuppressed by the dietary exposure. Examination of several other normal mouse chows revealed that they all contained casein as a protein source. A possible effect of prior exposure must be considered in all experimental animal studies involving immune responses to antigens which may be present in the environment.

Parameters affecting in vitro immunization of human lymphocytes

A method for the in vitro generation of antibody-secreting cells from human tonsil lymphocytes is described. Several parameters affecting such in vitro immunization have been studied in order to define optimal conditions for the production of specific antibody. In the presence of 15% of T-cell growth factors, lymphocytes prepared by Ficoll-Paque centrifugation increased 2.5 times over a period of 6 days. The major factors triggering specific antibody production against Haemophilus influenzae type b outer membrane preparations were: the use of tonsil lymphocyte cultures instead of peripheral blood lymphocytes, foetal calf serum instead of human serum, T-cell growth factors as a non-specific lymphocyte activator, low concentrations of antigen ranging from 1 to 10 ng/ml, a cell concentration of 4 X 10(6) cells/culture, and finally the removal of OKT8 positive suppressor T-cells. Under these conditions, a maximum antibody production was achieved after 7 days of culture and specific antibody response was obtained after in vitro immunization of tonsil lymphocytes from 10 out of 11 individuals tested.

Influence of TPA (12-O-tetradodecanoyl-phorbol-13-acetate) on human B lymphocyte function

The effect of the tumour-promoting agent TPA (12-0-tetra-dodecanoyl-phorbol-13-acetate) on the proliferation and Ig secretion response of blood and tonsil lymphocytes was investigated and compared to that of the T-cell-dependent polyclonal activators pokeweed mitogen (PWM) and group A streptococcal cell membranes (A-ScM) or the T-cell-independent B cell mitogen Staphylococcus aureus Cowan I (SAC) and a T-cell-independent B cell activator Klebsiella pneumoniae (Klebs M). In blood mononuclear cells (MNC), a rather weak, monocyte-dependent DNA synthetic response was observed after exposure to TPA, in comparison to PWM, A-ScM or SAC. Whereas highly purified B cells did not respond to TPA, purified T cells proliferated to a similar degree as unseparated MNC; moreover, the addition of T to B lymphocytes enhanced proliferation rates proportionally to the number of T cells added. This suggests that TPA acts as a polyclonal T cell activator (PTA) for human blood and tonsil cells. Similarly, TPA induced only small amounts of Ig secretion in blood and in tonsil MNC, as determined by an ELISA assay, and no significant Ig secretion in highly purified B cells. The rather weak B cell differentiation response was not due to a monocyte suppressor effect, since partially monocyte-depleted MNC or B cells responded similarly to the non-depleted cells. Thus, TPA cannot be considered as an alternative to other B cells stimulators, both with regard to DNA synthesis and Ig secretion.

A simple, rapid, reliable reverse haemolytic plaque assay and positive quality control test for routine use

A simple, rapid, reliable protein A reverse haemolytic plaque assay is described. Monolayers of protein A-coupled sheep red blood cells, in liquid medium, are formed in shallow 15 mm diameter chambers of the type commercially available for leucocyte migration inhibition assays. No agarose is necessary and the chambers are quick and easy to use, economical of reagents, and of a constant size and volume. Results compare favourably with those obtained using Cunningham chambers. The assay is ideal for clinical studies in which large numbers of samples are assayed daily. A positive quality control test for the protein A reverse hemolytic plaque assays is described. Spleen cells are stimulated with pokeweed mitogen to give high numbers of secreting cells. The cells are harvested on day 6 of culture and stored in aliquots at -70 degrees C. When thawed and tested in the protein A assay, these secreting cells form a sensitive and reproducible monitor of the day-to-day performance of the assay. Variation between operators and between batches of reagents may also be checked if desired, with little additional time, effort or expense.

Human T-lymphocyte response in vitro to synthetic peptides of herpes simplex virus glycoprotein D

Immunization of mice with a synthetic peptide that corresponds to a murine antibody-defined immunodominant domain of herpes simplex virus (HSV) glycoprotein D (gD) induced neutralizing antibodies against HSV types 1 and 2 and protected animals against a lethal challenge with HSV type 2 (Dietzschold, B., Eisenberg, R., Ponce de Leon, M., Golub, E., Hudecz, F., Varicchio, A. & Cohen, G. (1984) J. Virol. 52, 431-435). We report here that human peripheral blood T cells from HSV-seropositive and -seronegative adult donors are activated by this synthetic peptide in vitro. Interleukin-2-dependent T-cell lines established from these cultures respond specifically to peptides containing residues 1-23 of HSV gD and to a panel of overlapping peptides within this domain. The T-cell proliferative response was maximal when the majority of interleukin-2-propagated T cells were of the helper phenotype and the peptides were at least 16 amino acids long. Peptides of 8 or 12 amino acids from the carboxyl terminus were nonstimulatory. Peptide-activated T-cell lines from sero-negative donors less than 11 years old could be established in vitro, but most cells were of the suppressor/cytotoxic phenotype and demonstrated no antigen-specificity when tested with the panel of synthetic peptides.

Immunoregulation of the in vitro anti-HBs antibody synthesis in chronic HBsAg carriers and in recently boosted anti-hepatitis B vaccine recipients

We report a study on immunoregulation of in vitro antibody to hepatitis B surface antigen (anti-HBs) synthesis induced by pokeweed mitogen (PWM) from peripheral blood mononuclear cells (PBMC) in chronic hepatitis B surface antigen (HBsAg) carriers and in 'high responders', (anti-HBs RIA ratio greater than or equal to 20 in serum), recently boosted with anti-hepatitis B vaccine. Anti-HBs was detected in 11 days PBMC supernatants (SN) from 24 out of 36 'high responders', but in none from 31 chronic HBsAg carriers, despite detectable amounts of polyclonal IgG and antibody to hepatitis B core antigen (anti-HBc) were produced. The lack of anti-HBs production by chronic HBsAg carriers did not seem to be determined by suppressor influences because T lymphocytes from the majority of chronic HBsAg carriers, co-cultured with 'high responders' PBMC did not suppress anti-HBs production. Co-cultures between HBsAg carriers T4 positive (helper/inducer) cells and allogenic 'high responder' non-T cells produced anti-HBs antibody, indicating that HBsAg carrier T cells are not deficient in this allogenic helper function under PWM stimulation. Allogenic cocultures between HBsAg carrier non-T cells and 'high responder' T4 positive cells failed in anti-HBs production: a specific B lymphocyte defect might be involved in the lacking anti-HBs synthesis in chronic HBV patients. Antigen-induced specific anti-HBs synthesis experiments indicate that B cells themselves seem to be the target for HBsAg-induced suppression of anti-HBs antibody response.

Functional characterization of human alloreactive T cell clones

We have investigated the functional activity of alloreactive T cell clones, generated by limiting dilutions of MLC blasts. Clones displaying helper, suppressor, or cytotoxic functions (against Class I or Class II HLA antigens) were identified, using proliferative, 51Cr-release, and hemolytique-plaque induction assays. To determine whether functionally distinct clones share determinants that trigger the AMLC reaction we have tested the capacity of selected clones to cross-stimulate each other in secondary AMLC. Our data suggest that AMLC stimulatory determinants are related to common structure antigens of the T cell receptor for alloantigen, since helper clones, for example, (TLC #19) can induce memory responses to suppressor (TLC #209) as well as cytotoxic (TLC #207) clones and vice versa. The AMLC system seems well suited for studying network regulations within the T cell compartment.

Presence of T-cell receptor mRNA in functionally distinct T cells and elevation during intrathymic differentiation

Understanding the differentiation of functionally distinct subsets of T lymphocytes is essential to unravel their crucial role in the immune response and awaits knowledge of the assembly and expression of genes encoding the T-cell receptor. Recently, we have cloned and sequenced complementary DNA that may specify part of the human T-cell receptor. The deduced protein sequence showed extensive similarity to the entire length of mammalian immunoglobulin light chains. In addition, sequences corresponding to this message undergo somatic rearrangements and are assembled from non-contiguous genomic sequences into a single mRNA molecule, a mechanism similar to those found in the generation of immunoglobulin messages. A related molecule from the mouse was also isolated independently by Hedrick et al. Here we show that the putative T-cell receptor mRNA is expressed at a relatively high level during intrathymic differentiation before decreasing about 10-20-fold in normal, mature peripheral blood T cells and that it can also be detected in T-cell clones with helper and cytotoxic functions, as well as in at least one clone with suppressor properties.

Polyclonal activation of canine B lymphocytes evaluated by a protein A reverse hemolytic plaque assay

This paper describes the optimal culture and assay conditions for the polyclonal activation of canine lymphocytes with pokeweed mitogen and the quantitation of immunoglobulin secreting plaque-forming cells (PFC) using a staphylococcal protein A-reverse hemolytic plaque assay. The assay permits the quantitation of total immunoglobulin secreting PFC as well as class-specific immunoglobulin secreting PFC. On the optimal day of culture, a mean of 176 IgA PFC/10(6), 575 IgM PFC/10(6), 1276 IgG PFC/10(6), and 2158 total PFC/10(6) cells were generated following polyclonal activation. This study provides a simple and reproducible assay for the delineation of the immunoregulatory mechanisms involved in the differentiation of canine B lymphocytes.

Detection of single antibody-secreting cells generated after in vitro antigen-induced stimulation of human peripheral blood lymphocytes

Culture and assay procedures are described for the generation and the subsequent detection of single antigen-specific antibody-secreting cells after in vitro stimulation of human peripheral blood lymphocytes with tetanus toxoid. Simple, specific and sensitive, this new assay-culture system is well suited for the analysis of specific antibody production in man.

Specific antibody synthesis in vitro. I. Technical considerations

Previously described methods for measuring specific antibody production in vitro are complex and frequently require the addition of a non-specific mitogen and 2 or more separate steps including a lymphocyte culture and then an antibody assay. In this report we present further details regarding a 1-step, non-mitogen requiring assay for specific antibody synthesis combining microculture and enzyme-linked immunoassay techniques. Peripheral blood mononuclear cells from recently immunized subjects are cultured in antigen-coated plastic wells and the specific antibody produced and adhered to the solid-phase antigen is measured in an enzyme-linked immunoassay. The production of specific antibody in vitro did not occur in lymphocyte preparations that were frozen, thawed and incubated, nor did it occur in cultures containing puromycin. T cell separation and remixture experiments indicated that T cells provide significant augmentation under the conditions of this assay. It is apparent that the antibody measured was synthesized in vitro and that cell-cell interactions are operant. The assay may prove useful in the assessment of immune competence and in determining in vitro the effect of certain biologic response modifiers on antibody production.

Enumeration of human immunoglobulin-secreting cells by the ELISA-plaque method: IgE and IgG isotypes

A new system is described for the enumeration of human immunoglobulin-secreting cells (ISC), based upon the ELISA methodology. In principle, putative ISC are incubated over a solid phase containing bound anti-Ig of the isotype being tested. Secreted Ig is immobilized at or near the point of release from the ISC, and the resulting Ig fingerprint of the ISC is then visualized by the sequential application of an anti-Ig-alkaline phosphatase conjugate, followed by a substrate-agarose overlay. The system is capable of detecting IgE-secreting cells, and pokeweed mitogen-stimulated IgG-secreting cells with sensitivity at least equivalent to the protein A hemolytic plaque assay.

T-cell regulation of polyclonal B-cell activation induced by extracts of oral bacteria associated with periodontal diseases

These studies were designed to examine the role of regulatory T cells in the polyclonal antibody response of human peripheral blood lymphocytes to extracts of bacterial isolates commonly associated with periodontal disease. Polyclonal antibody responses to the organisms tested were found to be T cell dependent, as are most of the B-cell activators in the human system. Functional T helper activity was resistant to 1,500 rads of irradiation. Optimal polyclonal antibody responses to the bacterial extracts occurred at a 3:1 T-cell-to-B-cell ratio, whereas pokeweed mitogen-induced responses peaked at a 1:1 ratio, suggesting a difference in T-cell regulatory influences in response to these activators. Purified populations of T helper and suppressor cells exerted potent regulatory control of the responses to the bacterial extracts. These findings support the conclusion that regulatory T lymphocytes exert a potent modulating influence over the polyclonal response to periodontally associated bacteria and may play an important role in regulating the lymphocyte response in the diseased site.

Synovial fluid and blood monocytes/macrophages in rheumatoid arthritis. Influence on polyclonal activation of autologous B lymphocytes

The regulatory role of synovial fluid monocytes/macrophages from patients with rheumatoid arthritis in terms of B lymphocyte activation was evaluated by a reverse haemolytic plaque-forming cell (PFC) assay. Macrophage-depleted blood mononuclear cells (BMC) failed to respond to pokeweed mitogen (PWM). With autologous synovial fluid macrophages added, the PFC responses of macrophage-depleted BMC increased, and optimal concentration for full restoration of the PFC responses ranged from 8 to 35%. Synovial fluid mononuclear cells (SMC) as well as macrophage-depleted SMC were not able to respond to PWM. Addition of irradiated autologous blood macrophages to SMC did not increase the SMC PFC responses. It is concluded that the regulatory properties of synovial fluid macrophages do not explain the low PFC response of SMC to PWM.

The regulatory roles of T4 and T8 subsets in tetanus toxoid-induced in vitro immunoglobulin production

A new mitogenic system for in vitro immunoglobulin production induced by tetanus toxoid is presented and the role of T4 and T8 subsets in tetanus toxoid-induced in vitro immunoglobulin production is investigated. Purified T, T4, T8, and B cells from normal individuals previously immunized but not boosted with tetanus toxoid were cultured in helper and suppressor assays and the number of immunoglobulin-secreting cells were enumerated after culture using a hemolytic plaque assay. The regulatory roles of T4 and T8 cells in this tetanus toxoid system were compared with the role of these subsets after pokeweed mitogen stimulation. Although most of the immunoglobulin produced in the tetanus toxoid system was polyclonal, there were differences in the time course, the magnitude of the responses, the radiosensitivity of the subsets, and optimal T- to B-cell ratios for immunoglobulin production which distinguish the tetanus toxoid and pokeweed mitogen systems.

A pre-amplified reverse hemolytic plaque assay

A pre-amplified reverse hemolytic plaque assay has been developed. Sheep red blood cells (SRBC) were coated with staphylococcal protein A (SPA) by the chromic chloride method. The protein A-coated SRBC (SPA-SRBC) was then pre-amplified with an appropriate amount of human class-specific Ig. The pre-amplified Ig-SPA-SRBC was used to detect class-specific Ig-producing cells. It was found that this pre-amplified reverse hemolytic plaque assay gave clearer, larger and more numerous hemolytic plaques which were easy to count and thus gave more accurate results.

Human B cell function in responder and non-responder individuals. II. The role of T helper cells in promoting the PWM-induced B cell production of immunoprotein

Sorted OKT4+ cells treated with pokeweed mitogen (PWM) and subsequently X-irradiated were used as a source of helper T cells to examine human T and B cell function. PWM-induced immunoprotein synthesis by human peripheral blood lymphocytes was the model used to study the cellular interactions. PWM was shown to induce helper T cell function which caused non-PWM treated B cells to secrete immunoglobulin. PBL from certain individuals could not be induced by PWM to secrete Ig therefore allogeneic co-cultures of helper T cells and B cells were examined to define the defective cell population. Ig synthesis in allogeneic cultures of T and B cells was always greater than that observed in autologous cultures when cells from responders were assayed. However, when allogeneic cultures were initiated using B cells from a responder and PWM treated T cells from a non-responder and examined for Ig synthesis, the B cell responses were markedly lower than seen in the autologous responder cultures. In addition, PWM activated helper T cells from a responder induced a significantly higher Ig synthesis by B cells from a non-responder. These observations indicate that PBL from individuals who do not respond in a PWM driven Ig synthesis assay have relatively normal B cell function but are deficient in helper T cell function.

Isolation and characterization of human B lymphocyte enriched populations. I. Purification of B cells by immune rosette depletion

In the present study we describe a technique for the preparation of a highly purified B cell population from peripheral blood mononuclear cells (PBMC) by immune rosette depletion of non-B cells utilizing monoclonal antibodies directed at T cells, monocytes and null cells. The non-rosetted population contains greater than 90% B cells after a single rosetting step. The technique is simple, rapid and reproducible and results in minimal cell loss. In contrast, the E rosette negative (E-) fraction contains approximately 20% B cells whereas the surface immunoglobulin positive (sIg+ population obtained by Sephadex-anti-F(ab')2 column chromatography is comprised of approximately 60-80% B cells.

Specific in vitro antimannan-rich antigen of Candida albicans antibody production by sensitized human blood lymphocytes

We have developed a new antigenic system for the induction of specific in vitro antibody response in man. The antigen used was purified from the cell wall of Candida albicans strain A and contained greater than 96% polysaccharide mannan. Peripheral blood mononuclear cells from Candida-sensitized donors produced specific antimannan antibodies during a 7-d culture in the presence of mannan absorbed with methylated bovine serum albumin. Two methods were used to detect antimannan antibody responses. Antimannan antibody-producing cells were identified by radioautography with tritiated mannan. Antibody concentration in culture supernatants was measured by an enzyme-linked immunosorbent assay. In both methods, specific IgM and IgG (but not IgA) antibodies were detected. The antibody production to mannan was specific, since an antigenically unrelated polysaccharide (pneumococcal antigen S III) did not bind to methylated bovine serum albumin-mannan-induced blast cells and did not induce antimannan antibody-containing cells. Furthermore, a pulse with an excess of unlabeled mannan abolished [3H]mannan binding, whereas an excess of unlabeled S III did not. Similarly, no antimannan antibody was obtained in influenza virus-stimulated cultures and mannan-stimulated cultures were not inducing antiinfluenza antibodies. The antimannan antibody production was shown to be a T cell-dependent phenomenon. The T helper effect appeared to be radiosensitive. It was under a genetic restriction as it occurred only in autologous or semi-identical but not in allogeneic situations. This system is relatively simple, reproducible, and well suited for the study of specific secondary in vitro antibody responses to polysaccharide antigens in humans.

T-cell subsets in human lymphocytes maintained in IL-2 medium after PHA or mixed lymphocyte reaction activation

The culture of human T lymphocytes in interleukin-2 (IL-2) containing growth factor medium results in a significant shift in the T-lymphocytes subsets isolated from such cultures at weekly intervals. If normal peripheral blood mononuclear cells are stimulated with phytohemagglutinin (PHA) or in a mixed lymphocyte reaction (MLR), the resulting T lymphoblasts can be propagated in growth factor medium. Staining of the cultured cells with monoclonal antibodies was evaluated by indirect immunofluorescence on a laser-activated flow cytometer (Ortho Spectrum III). The antibodies used were: OKT3 (mature T lymphocytes), OKT4 (helper/inducer T lymphocytes), OKT8 (cytotoxic/suppressor T lymphocytes, OKT10 (immature and "activated" lymphocytes), OKT11a (cells which rosette with sheep erythrocytes), and OKIa-I (HLA-DR constant region). Both PHA and MLR activation resulted in initial preservation of the OKT4+ subset predominance over OKT8+ T lymphocytes noted on normal circulating blood lymphocytes. However, during culture in T-cell growth factor medium, there was a progressive increase in the percentage of OKT8+ cells, and a concomitant decrease in OKT4+ lymphoblasts. The increase in OKT8+ cells in the MLR-stimulated cultures was paralleled by an increase in specific cell-mediated cytotoxicity against the stimulating lymphocyte population. In addition to the shift in T-lymphocyte subset, there was virtual 100% staining with OKT3 and OKT11a, indicating the T-cell nature of the proliferating cells. OKT10 which was present on a small subset of fresh blood lymphocytes appeared rapidly in stimulated cultures, and was retained on virtually all lymphoblasts of either OKT4+ or OKT8+ subset. OKIa-1 cells increased slowly in PHA-stimulated cultures. HLA-DR+ T cells were detected earlier in MLR cultures. The activation of T lymphocytes results in a significant increase in the number of molecules of OKT11a bound per cell, in concert with the increased avidity of T lymphoblasts for sheep erythrocytes. The significant change in the phenotype and function of lymphoblasts isolated from long-term cultures demonstrates the importance of monitoring cultures, and the potential hazards in equating a cultured cell population with a freshly isolated one.

Polyclonal activation of immunoglobulin secretion without prior DNA synthesis in human B lymphocytes induced by Klebsiella pneumoniae

The capacity of various cell preparations of Klebsiella pneumoniae K43 (Klebs) to induce [3H]thymidine uptake and immunoglobulin (Ig) secretion by human mononuclear blood cells (MNC) and their lymphocyte subpopulations was investigated. All Klebs preparations were virtually devoid of mitogenic properties, in contrast to control preparations of pokeweed mitogen (PWM) and group A streptococcal cell membranes (A-ScM). Klebs induced differentiation of B cells into Ig-secreting cells. B-cell populations that were sufficiently depleted of T cells to be unresponsive to A-ScM ("highly purified B cells") showed a marked response to Klebs. Similarly, the number of plaque-forming cells (PFC) in Klebs-driven cultures did not change after restitution of T cells, whereas the presence of restituted T cells augmented the B-cell response to PWM and A-ScM. Radical removal of adherent MNC ("monocytes"), however, completely abrogated the PFC response and [3H]thymidine uptake of both MNC activated by Klebs and MNC activated by PWM or A-ScM.

Use of nuclear antigen-coated red cells in hemolytic plaque assays

By studying antinuclear antibody production at the cellular level, we can better understand the problems of immunoregulation in individuals with systemic lupus erythematosus. To date, the use of hemolytic plaque assays to detect B cells secreting antinuclear antibodies has been hampered by an inability to achieve reliable coating of red cells by nuclear antigens. Because the chromic chloride technique has proved ineffective for coupling nucleic acids and/or nuclear antigens to sheep red blood cells (SRBC) in our laboratory, we have developed a method of coupling SS DNA, DS DNA, poly(I).poly(C), Sm, and ENA to red cells pretreated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (ECDI) and poly(L-lysine) (PLL). Coated red cells were agglutinated by specific antisera and not by normal sera and were then used in hemolytic plaque assays to detect antinuclear plaque-forming cells (PFC) in spleens from various strains of mice with lupus-like syndromes. PFC specific for SS DNA, DS DNA, poly(I).poly(C), Sm, and ENA were found in MRL/lpr and NZB x W mice, and the number of anti-SS DNA and anti-DS DNA PFC correlated with the age of the animals. Indirect (IgG) PFC specific for nuclear antigens increased dramatically in female NZB x W mice between 11 and 13 months, a time when more than 50% of the animals usually die. Preliminary studies have shown that PFC specific for nuclear antigens can be detected in peripheral blood from patients with lupus erythematosus. Pretreatment of sheep red cells with ECDI and PLL thus allowed the coupling of selected nuclear antigens to these cells and provided the first demonstration of IgM and IgG PFC specific for a variety of nuclear antigens.

In vitro analysis of lymphocytes: markers and functions

Current dermatologic literature is becoming replete with articles elucidating current concepts in the pathophysiology of lymphocytic diseases. Much of this knowledge emanates from the increasingly sophisticated and complex methods of identifying lymphocytes. No longer does it suffice to know that B lymphocytes or T lymphocytes are present, but rather the key information involves knowing what subsets of these cells are present and/or their functional status. The reader attempting to assimilate all this information is thus confronted with an overwhelming, as well as frequently changing, array of analytic methods. This paper is presented as a review of thinking, principles, and methods employed in research on lymphocytic disease.

In vitro humoral immune response of human peripheral blood lymphocytes to tetanus toxoid sepharose 4B

The in vitro immune response of unfractionated human peripheral blood lymphocytes (PBL) from immune donors who had not been re-immunized with tetanus toxoid (TT) prior to donation was investigated. In this study we were able to stimulate PBL with tetanus toxoid coupled to Sepharose 4B (STT) for production of anti-tetanus toxoid antibody (Ab). Soluble tetanus toxoid or STT alone did not stimulate production of specific Ab. Pokeweed mitogen (PWM) and STT were required for optimal production of IgG and IgM antibodies specific to tetanus toxoid. Specific Ab responses were reduced in low and high concentrations of STT. Depletion of monocytes had no effect on either total IgG or specific IgG synthesis, but decreased the synthesis of both total and specific IgM. Depletion of E-rosette-forming cells decreased the production of specific Ab, suggesting T-dependency of the immune response to STT. Simultaneous production of total immunoglobulin and specific Ab by Sepharose 4B was negligible in the absence of PWM. In the presence of PWM, total immunoglobulin production was optimal, and specific anti-TT Ab production was undetectable. The specificity of the anti-TT Ab was studied by absorption of the culture supernates with an STT column which removed all measurable specific Ab.

Staphylococcal protein-A is a potent T-cell mitogen of tonsillar lymphocytes

Optimal conditions for the stimulation of human tonsillar lymphocytes by staphylococcal protein-A (SpA) are described. By stimulating fractions enriched or depleted of E-rosette forming cells, the response was shown to be predominantly a T-cell response. A comparison of stimulation by SpA with that of phytohaemagglutinin (PHA) proved SpA to be a potent T-cell mitogen. We suggest that SpA may be another useful mitogen for studying human T-cell growth and differentiation.

Human cytotoxic T lymphocytes (CTL) induced by phytohemagglutinin: conditions for CTL generation and effect of interferon

The present study demonstrates that human peripheral blood mononuclear cells (PMC) can be stimulated in vitro to become cytotoxic T lymphocytes (CTL) by PHA. A significant cytotoxic activity of PMC was detected 48 hr after the culture initiation in the presence of 5 micrograms/ml of PHA and the peak level of the activity was obtained by culturing PMC for 72 hr. The cytotoxic cells require the presence of PHA as a cell agglutinin for the expression of their cytotoxic activity. The effector cells mediating the activity were identified as T lymphocytes by E-rosette fractionation of PMC. In this system, removal of carbonyl iron phagocytosed or attached cells from PMC did not abrogate CTL generation of PMC. In addition, human alpha-interferon did not augment CTL generation or expression of their activity. Although the target cells employed were sensitive to natural killer (NK) cells, the effector cells induced by PHA did not seem to have any relation to the NK cells. The present study may provide a useful tool to analyze for precursors of killer T cells.

Functional activity of peripheral mononuclear cells in cystic fibrosis: antibodies and plaque formation

Chronic pulmonary infection is known to constitute a major complication of cystic fibrosis (CF). In order to determine whether a defect of antibody formation is associated with this clinical finding, we have investigated antibody production on the cellular level by using a haemolytic plaque forming cell (PFC) assay. The ability of peripheral mononuclear cells (MNC) derived from patients with CF to form PFC upon stimulation by pokeweed mitogen was significantly decreased as compared to healthy control individuals (P less than 0 . 01). Levels of serum immunoglobulins of the G, A, and M classes and of sheep red blood cell agglutinating antibodies were estimated as well, but no correlation was obtained between these parameters and the number of PFC in patients with CF.

Specific in vivo and in vitro antibody response to tetanus toxoid immunization

Booster immunization of normal individuals with soluble tetanus toxoid (TT) produced significant levels of plasma anti-tetanus IgG and IgM detectable by an enzyme linked immunosorbent assay (ELISA). Similar changes in circulating anti-TT antibody were found in mice following primary immunization. There was. however, no correlation observed between circulating anti-TT antibody response and the proliferative response of peripheral blood mononuclear cells exposed to soluble TT in the immunized individuals. The capacity of the peripheral blood mononuclear cells to produce specific anti-TT antibody in vitro was evaluated using a new microculture antibody synthesis enzyme-linked assay (MASELA). It was observed that the production of specific antibody in vitro correlated with the circulating anti-TT antibody level and not with the proliferative response. Peripheral blood mononuclear cells from these recently secondary immunized individuals produced greater specific anti-TT antibody when cultured in TT coated plastic wells than did controls. The potential utility of this technique in assessing response to immunization and basic immune competence is discussed.

Are mitogenic sera necessary for the generation of human plaque-forming cells?

Human plaque-forming cells (PFC) have been quantitated following pokeweed mitogen stimulation by a protein A plaque technique using human erythrocytes. The PFC are generated in cultures supplemented with non-mitogenic human AB serum of foetal bovine serum (FBS) of varying degrees of inherent mitogenicity. In the latter case, no correlation exists between the mitogenicity of the serum supplement used in these cultures and the PFC response obtained. This fact, in addition to the demonstrated usefulness of the AB sera in facilitating the generation of PFC makes it unlikely that serum mitogenicity is a requirement for in vitro human immunoglobulin synthesis and secretion.

Humoral immunity in leprosy: immunoglobulin G and M antibody responses to Mycobacterium leprae in relation to various disease patterns

A solid-phase radioimmunoassay, applying whole Mycobacterium leprae as antigen and radiolabeled protein A from Staphylococcus aureus as antibody-detecting reagent, was used for the determination of specific immunoglobulin G (IgG) and IgM antibody responses in leprosy patients. High IgG anti-M. leprae antibody levels were found in lepromatous leprosy patients, whereas the antibody response in tuberculoid leprosy patients varied from negative, i.e., comparable with responses measured in normal individuals, to strongly positive. In tuberculoid leprosy patients, a significant increase in IgG anti-M. leprae antibody levels was observed in the more widespread forms of the disease, but positive antibody responses were especially predominant among patients with active lesions. Lepromatous leprosy patients generally demonstrated high levels of both IgG and IgM anti-M. leprae antibodies, but no relation was found between the antibody responses and bacillary load or other clinical parameters. A marked decrease in specific IgG and IgM antibody levels was observed in lepromatous leprosy patients during their first year of treatment. Differences in mechanisms regulating the humoral immune response in tuberculoid and lepromatous leprosy patients were indicated, and the application of antibody assessments in leprosy control programs is discussed.