Enumeration of (auto)antibody producing cells in human using the "spot-ELISA"

A single strain of Mycobacterium bovis bacillus Calmette-Guérin (BCG) grown in two different media evokes distinct humoral immune responses in mice

Two attenuated bacillus Calmette-Guérin (BCG) preparations derived from the same Moreau strain, Copenhagen but grown in Sauton medium containing starch and bacto-peptone (onco BCG, O-BCG), or asparagine (intradermal BCG, ID-BCG), exhibited indistinguishable DNA sequences and bacterial morphology. The number of viable bacilli recovered from spleen, liver and lungs was approximately the same in mice inoculated with the vaccines and was similarly reduced (over 90%) in mice previously immunized with either BCG vaccine. The humoral immune response evoked by the vaccines was, however, distinct. Spleen cell proliferation accompanying the growth of bacilli in tissue was significantly higher in mice inoculated with O-BCG. These cells proliferated in vitro upon challenge with the corresponding BCG extract. Previous cell treatment with mAb anti-CD4 T cells abolished this effect. Anti-BCG antibodies, as assayed either in serum by ELISA or by determining the number of antibody-producing spleen cells by the spot-ELISA method, were significantly higher in mice inoculated with ID-BCG. Anti-BCG antibodies were detected in all immunoglobulin classes, but they were more prevalent in IgG with the following distribution among its isotypes: IgG1>(IgG2a = IgG2b)>IgG3. When some well-characterized Mycobacterium tuberculosis antigens were used as substitutes for BCG extracts in ELISA, although antibodies against the 65-kDa and 96-kDa proteins were detected significantly, antibodies against the 71-kDa, 38-kDa proteins and lipoarabinomannan were only barely detected or even absent. These results indicate that BCG bacilli cultured in Sauton-asparagine medium permitted the multiplication of bacilli, tending to induce a stronger humoral immune response as compared with bacilli grown in Sauton-starch/bacto-peptone-enriched medium.

Expression of mouse CD43 in the B cell lineage of transgenic mice causes impaired immune responses to T-independent antigens

CD43 (leukosialin), a sialylated glycoprotein expressed on the surface of most hematopoietic cells, has been implicated in cell adhesion and signaling. However, its precise physiological function remains unclear. We used mouse CD43 (mCD43)-immunoglobulin enhancer-transgenic (TG) mice to study the role of mCD43 in vivo. Previous work revealed that mCD43 expression on mature B cells in these mice resulted in immunodeficiency to T-dependent (TD) antigens (Ag), possibly by impairing B-T cell interactions. In the present study we have immunized the TG mice with the T-independent (TI) Ag fluorescein-(Fl) lipopolysaccharide (LPS) (TI type 1 Ag) and Fl-Ficoll (TI type 2 Ag). Surprisingly, the mCD43-Ig enhancer expressing mice were impaired in their ability to mount humoral responses to both Fl-LPS and Fl-Ficoll, and had decreased numbers of cells responding to Ag in vivo. Flow cytometric analysis was performed on peritoneal B-1 cells, a population which often plays a major role in humoral responses to TI Ag such as bacterial Ag. This analysis revealed similar B220, IgM and CD5 expression patterns for the TG and nontransgenic (NTG) B-1 cells. In addition, purified peritoneal B-1 cells from TG and NTG mice were able to respond to LPS. Stimulation of splenic B cells in vitro with Fl-LPS and Fl-Ficoll revealed that, in contrast to NTG B cell responses, TG B cell responses could not be enhanced by co-culture with T cells. However, soluble T cell factor enhancement of the TG B cell responses was normal. These data suggest that the mCD43 expression on B cells may inhibit cell interactions that are important for enhanced TI Ag responses. The anti-adhesive forces of mucins in general may thus be critical in regulating both TD and TI humoral responses.

Impaired antigen-specific B-cell response and altered splenic microstructure in mice following continuous administration of IL-4 in vivo

The effect of long term in vivo administration of IL-4 on the induction of antigen-specific B cells, the splenic microenvironment and the yield of antigen-specific antibody producing hybridomas was studied. Immunization with DNP-KLH, followed by 12 weeks continuous IL-4 treatment resulted in increased numbers of total splenic (non-DNP) IgM and IgG AFC (antibody forming cells) on day 5 after booster, whereas the DNP-specific IgG and IgG1 AFC were reduced compared to age-matched control animals not treated with IL-4. In addition, an almost 300-fold increase in non-DNP IgE was found while the IgE anti-DNP response was minimal. When the splenic cells were used in a fusion protocol, a relative decrease in yield of antigen-specific hybridomas was found in the long term IL-4 treated mice. Immunohistological staining of spleen sections from mice treated with IL-4 up until the time of booster revealed reduced B-cell follicle area and germinal centre numbers. These results show that extensive IL-4 treatment reduced antigen-specific B-cell formation and suggests a reduction in the number of B cells entering the memory B-cell pathway in the spleen.

Humoral immune response to Salmonella abortusovis in sheep: in vitro induction of an antibody synthesis from either sensitized or unprimed lymph node cells

In vitro culture conditions were determined to induce an anti-Salmonella abortusovis antibody synthesis from lymph node leucocytes of three immunized sheep and two unprimed lambs maintained in culture in the presence of heat-inactivated bacteria for 2 weeks. Humoral immune responses were assessed by enumerating specific antibody-secreting cells using ELISASPOT and by titrating immunoglobulins secreted into culture supernatants using ELISA techniques. Optimal secondary antibody response was observed from cultures performed with fetal calf serum (compared with horse serum) and with an antigen concentration of one to ten bacteria per cell. This kind of antigenic stimulation allowed induction of numerous antibody-secreting cells without adsorption of the secreted antibodies. Maximal numbers of antibody-secreting cells could reach a rate of 1% of the sheep leucocytes initially put into culture. Kinetic profiles of antibody production from boosted lymph node cells were characterized by an ascending phase from the sixth to the twelfth day of culture and then showed a plateau phase until Day 14. Most of the responses were composed of IgM and IgG1 antibodies, traces of IgG2 being detected at the end of experiments. From the twelfth day of antigenic stimulation, the IgM isotype was preferentially expressed with high antigen concentration (100 bacteria per cell), whereas the highest amounts of IgG1 were detected at lower concentration (one to ten bacteria per cell). While anti-Salmonella IgM appeared to be mainly specific for the lipopolysaccharide (LPS) cell wall fraction, some IgG1 recognized other bacterial antigens. Kinetic profiles and magnitudes of primary antibody responses induced in vitro from lamb lymph node cells did not differ from those defined in cultures of sheep boosted leucocytes. But these immune reactions were mainly made up of anti-LPS IgM. Few anti-Salmonella IgG1 were detected from the tenth day of culture. So these in vitro assays allowed induction of antibody synthesis from either in vivo sensitized or unprimed sheep lymph node leucocytes. This methodology would permit achievement of more detailed studies on interactions between Salmonella and lymph node leucocytes, leading to a better understanding of the mechanisms controlling bacterial dissemination through the lymphoid tissue.

Age-related changes of the antigen-specific antibody formation in vitro and PHA-induced T-cell proliferation in individuals who met the health criteria of the Senieur protocol

The antigen-specific antibody secretion in vitro after immunisation with the primary T-cell dependent antigen Helix pomatia Haemocyanin (HPH) was investigated in both young and elderly individuals, who all met the health admission criteria for immunogerontological studies as detailed in the SENIEUR protocol. In addition, elderly non-Senieur persons were incorporated in this study. Young and elderly Senieur volunteers were fully comparable in terms of the occurrence of anti-HPH antibody secreting cells after in vitro simulation of peripheral blood mononuclear cells with variable doses of the antigen. In contrast, the non-Senieur elderly showed a lower number of anti-HPH antibody secreting cells in vitro. PHA-conditioned medium did enhance this in vitro response, whereas the addition of IL-2 remained ineffective. The PHA-induced T-cell proliferation was found to be somewhat impaired in elderly Senieur individuals and significantly lower in elderly non-Senieur individuals compared to young healthy persons. Using an immunofluorescence double staining technique after BrdU incorporation, the phenotype of the proliferating cells was determined. Again the total number of proliferating cells was impaired in the non-Senieur elderly. No changes in the relative contribution of CD4+ or CD8+ cells to the number of proliferating cells were found in the different age groups. On the other hand, a significantly lower number of proliferating cells with IL-2 receptor expression were detected in the non-Senieur individuals, which could account for the lack of response to IL-2 in this group. Our study clearly shows that so-called age-associated immune deficiency can be the result of disease and not necessarily of the ageing process itself.

Increased production of antigen-specific B lymphocytes during in vitro immunization using carrier-specific T helper hybridomas

An in vitro method to increase the production of hapten-specific antibody-forming B cells (AFC) using a carrier-specific T helper hybridoma and murine splenocytes is described. Naive splenocytes (6 x 10(6)/ml) are cultured in vitro in the presence of a hapten-carrier conjugate (DNP.OVA) and OVA-specific T helper hybridomas (0.5 x 10(6)/ml). After 4-5 days in vitro immunization (IVI), the maximum number of DNP-specific AFC were found using a spot-ELISA with twice the number of IgM positive cells as IgG positive AFC. The presence of antigen in the form of a hapten-carrier complex and the use of a carrier-specific Th hybridoma resulted in more hapten-specific AFC than when neither antigen nor Th hybridoma were present or when antigen alone or T help alone were used. Also when the hapten was conjugated to a carrier not recognised by the carrier-specific Th hybridoma there were considerably fewer (less than 50%) hapten specific AFC formed. When in vivo primed splenocytes (DNP) were boosted in vitro (IVB) under the same conditions as for IVI most hapten-specific AFC were found on day 4 and both anti-DNP IgM and IgG AFC were increased relative to IVI. Again most AFC were found when hapten was bound to the relevant carrier. In conclusion, carrier-specific T hybridomas can be used in an in vitro immunization procedure with naive or primed splenocytes to increase the frequency of anti-hapten AFC. This method offers an improvement over the current in vitro immunization procedures for the production of monoclonal antibodies.

An isotype-specific spot-ELISA for the enumeration of antibody-secreting hybridomas and the determination of isotype switch variants

A solid-phase spot enzyme-linked immunosorbent assay (spot-ELISA) using rat monoclonal antibodies (MAbs) and an image-processing system is described. This isotype-specific spot-ELISA permits the enumeration of antibody-secreting cells irrespective of the specificity of the secreted antibodies. When used in combination with an ELISA, the antibody production per cell can also be evaluated. In addition, isotype switch variants, which arise spontaneously in antibody-producing cell lines, can be determined. This study compared four assays: three antigen-specific spot-ELISAs, using enzyme-conjugated polyclonal antibodies as well as rat MAbs; and an isotype-specific spot-ELISA using rat MAbs. There were no significant differences between these four spot-ELISA systems. For one tested cell line (alpha huIgA1/gamma 1), the number of antibody-secreting cells fluctuated between 60% and 95% during several passages. For the other tested cell line (alpha huIgA1/gamma 2b), the number of antibody-secreting cells decreased from 90% to 70% after several passages. The results of the spot-ELISA were in agreement with flow cytometric (FC) analysis of cytoplasmic IgG. This indicates that for these two cell lines, the synthesized IgG was also secreted into the culture fluid. Using the isotype-specific spot-ELISA, the switch frequency of five murine hybridomas (alpha huIgA1/gamma 1, alpha huIgA1/gamma 2b, alpha HRP, RIV6, MN12) was determined. The switch frequencies varied from 1/82,000 for the alpha HRP cell line to 1/660,000 for the alpha huIgA1/gamma 2b cell line.

A prospective study of in vitro anti-HBs producing B cells (spot-ELISA) following primary and supplementary vaccination with a recombinant hepatitis B vaccine in insulin dependent diabetic patients and matched controls

A prospective study of the immune response after hepatitis B vaccination was carried out in 32 insulin dependent diabetes mellitus (IDDM) patients and their age and sex matched healthy controls. A sensitive, immunoenzymatic technique was used, able to detect in vitro specific antibody production by mitogen stimulated individual B cells. In-vivo serologic response after vaccination with a standard scheme (0, 1 and 6 months) of 20 micrograms recombinant hepatitis B (HB) vaccine was significantly impaired in the IDDM patients both with respect to the number of nonresponders (25 versus 3%, P less than 0.05) and antibody titers reached (1,377 vs. 9,060 IU/L, P less than 0.05). The total number of in vitro IgM- and IgG-class immunoglobulin producing B cells as detected by the spot-ELISA, was found to be comparable in both groups. Specific IgG anti-HBs (and to a lesser extent IgM anti-HBs) showed impairment in the diabetic population as a whole. The number of IgG anti-HBs producing B cells was markedly depressed one month following vaccination, which is probably a reflection of homing of B cells outside the circulation. Responding subjects were identified early during their vaccination by the detection of in vitro anti-HBs production using the spot-ELISA. Non-responding healthy subjects and IDDM patients as a group showed a low number of IgG anti-HBs spots, suggesting a reduced specific memory B cell frequency. In 13 of 15 hypo- and nonresponders with positive IgG anti-HBs spots supplementary vaccination(s) resulted in improved anti-HBs levels.

Quantitative clonal analysis of the B cell repertoire in human lupus

To gain further insight into the origin of autoantibody hyperproduction in human lupus, we quantitated the B cell repertoire toward exogenous and self-antigens. Using the Spot-ELISA method and two panels of nine exogenous and 10 self-antigens, we found that the normal human immune repertoire comprises a high frequency of B cell precursors secreting IgM antibodies to self- and exogenous determinants. This repertoire was markedly deficient in precursors producing IgG able to bind self-antigens. In lupus patients, the absolute numbers of clone precursors of the immune repertoire expressing IgM receptors whose paratopes impart affinity to self- and exogenous determinants were higher than in control individuals. Additionally, IgG antibody-forming cell precursors with binding specificity for lupus-associated antigens were detectable in the repertoire of these patients. Based on these results, we propose that hyperproduction of human lupus-associated autoantibodies arises in a two-stage mechanism whereby a general activation of the multireactive immune B cell repertoire precedes an oligospecific expansion of selected B cell clonotypes.

The use of monoclonal antibodies in an enzyme immunospot assay to detect isotype-specific antibody-secreting cells in pigs and chickens

Monoclonal antibodies directed against porcine immunoglobulin isotypes G, G1, G2, M, and A and against chicken immunoglobulin isotopes G, M, and A were tested in an antigen-specific spot-forming cell (SFC) assay based on the principle of the enzyme immunoassay. The SFC assay was used to quantitate ovalbumin (OA)-specific antibody-secreting cells (ASC) in pigs that had been primed and boosted with OA. The SFC assay was also used to quantitate trinitrophenyl (TNP)-specific ASC in chickens that had been primed with TNP-conjugated keyhole lympet haemocyanin (TNP-KLH). Although, the classical plaque-forming cell (PFC) assay cannot reliably detect isotope-specific ASC in pigs and chickens, it can detect these cells in mice. Therefore, we compared the OA- and TNP-specific SFC assays with PFC assays that were specific for these antigens in mice. The study demonstrated that the SFC assay is superior to the PFC assay in detecting both OA-specific ASC and TNP-specific ASC. The frequencies of OA-specific and TNP-specific SFC detected in mice were of the same order of magnitude as those detected in pigs and chickens. We concluded that the SFC assay is the better method for quantitating ASC in pigs, chickens, and probably all domestic animals for which isotype-specific monoclonal antibodies are available.

Anti-DNA antibody production by CD5+ and CD5- B cells of patients with systemic lupus erythematosus

Although the presence of anti-DNA antibody is a hallmark of systemic lupus erythematosus (SLE), neither the subsets of B cells that secrete anti-DNA antibody nor the stimuli responsible for the induction of anti-DNA secretion is known. In particular, the role of CD5+ B cells in human SLE, a distinct subpopulation of antibody-secreting cells shown previously to be a source of anti-DNA antibody in murine models of SLE, is unknown. To approach these questions, we developed a sensitive enzyme-linked immunospot (ELIspot) assay to measure spontaneous secretion of antibody to single-stranded (ss) DNA, double-stranded (ds) DNA, tetanus toxoid, and polyclonal immunoglobulin (Ig) by purified CD5+ and CD5- B cells of 15 SLE patients and 15 healthy control subjects. The B cells of only 1 of 15 healthy subjects secreted a significant level of anti-ssDNA antibody, and none secreted anti-dsDNA. By contrast, in the majority of SLE patients both CD5+ and CD5- B cells secreted IgG and/or IgM anti-ssDNA as well as anti-dsDNA antibody. Further analysis of the anti-ssDNA response revealed that the level of IgG and IgM anti-DNA antibody secretion by CD5- B cells correlated closely with the level of polyclonal Ig production by the same subpopulation (r = 0.81 and 0.70, respectively). In contrast, production of anti-DNA by CD5+ B cells occurred independently of polyclonal Ig production by both CD5+ and CD5- B cell subpopulations. These results suggest that in human SLE there exist two anti-DNA antibody-producing B cell subpopulations with distinct induction mechanisms: one (CD5+), which independently secretes anti-DNA, and another (CD5-), which produces anti-DNA as an apparent consequence of polyclonal B cell activation.

Detection and isolation of antigen-specific B cells by the fluorescence activated cell sorter (FACS)

A method is described for the isolation of antigen-specific B cells from immunized and subsequently boosted mice. Antigen-specific B cells were stained by incubation with fluorescein isothiocyanate (FITC)-labelled antigen and then detected and isolated in a fluorescence activated cell sorter (FACS). Ovalbumin (OVA) and Helix pomatia haemocyanin (HPH) were used as antigens in this procedure, yielding relative amounts of antigen-FITC-binding lymphocytes of 0.9 +/- 0.4% and 3.5 +/- 3.1%. The FITC-positive cells were visible as distinct cell populations in the FACS-generated histograms. All antigen-FITC-binding cells were B cells, as shown by double staining with phycoerythrin-conjugated anti-mouse Ig In addition, as tested in a spot-ELISA, the sorted, antigen-FITC-binding cell population contained almost the entire population of antigen-specific antibody-producing B cells. However, sorting had a negative influence on the antibody production capability of the sorted cells. Through washing of isolated spleen cells in the procedure before labelling with antigen-FITC proved to be essential for the specific detection of antigen-specific B cells, since staining without prior washing resulted in antigen-FITC binding to all B cells. This 'nonspecific' staining phenomenon was caused by the presence of antibodies, specific for the immunizing/boosting antigen, which were also present in the spleen cell suspension. These antibodies formed immune complexes with antigen-FITC and bound to Fc receptors present on all B cells, interfering in this way with any specific binding of antigen-FITC to sIg on the B cells.

Generation of high-rate ovalbumin-specific antibody-secreting cells in cultures of human peripheral blood B cells obtained from non-immunized blood donors

When human peripheral blood B cells are cultured for 6 days with the T cell-dependent peptide antigen ovalbumin (OA) in the presence of antigen-presenting cells and helper T cells, plaque-forming cells (PFC) are generated. These OA-induced PFC differ from the conventional high-rate antibody-secreting PFC formed after stimulation of B cells with recall antigens (e.g. tetanus toxoid) in that they secrete antibody at a very low level. Previous studies have shown that OA-induced PFC are B lymphocytes in an early activation state rather than cells that have differentiated into plasmablasts. The apparent arrest in the maturation of OA-induced PFC in an early activation phase can be overcome by simultaneous stimulation with interleukin 2 (IL-2) and gamma interferon (IFN-gamma). The isotype of the OA-specific antibodies secreted, however, are only of the IgM class, demonstrating that an isotype switch does not occur.

Detection of IgA antibodies and quantification of IgA antibody-producing cells specific for ovalbumin or Trichinella spiralis in the rat

This report describes procedures to quantify IgA responses in the rat sensitized to ovalbumin or infected with the parasite Trichinella spiralis: an ELISPOT detecting specific IgA antibody-producing cells in lymph nodes, and an ELISA demonstrating IgA antibody in serum and gut mucosal scrapings. For this purpose a mouse monoclonal anti-rat IgA antibody was produced. This IgG1-kappa 1 antibody recognized rat IgA but not rat IgM, IgG, or IgE. It proved very suitable in both assays. Using this reagent we could demonstrate large numbers of IgA anti-ovalbumin-producing cells in the mesenteric lymph nodes 15 days after sensitization to ovalbumin via the Peyer's patches. At 28 days after sensitization the numbers were much lower. IgA antibody titres to ovalbumin in serum were maximal between days 14 and 21 after immunization. Maximal numbers of IgA anti-T. spiralis-producing cells were found in the mesenteric lymph nodes 12 days after infection with muscle larvae, followed by a sharp decrease at 15 days. Maximal IgA anti-T. spiralis antibody titres in serum and mucus scrapings of small intestines were found on days 10 and 12 after oral infection with the parasite.

Novel ELISA and ELISA-spot assays used to quantitate B cells and serum antibodies specific for T cell and bromelated mouse red blood cell autoantigens

The frequency of splenic B cells producing antibodies reactive with bromelain-treated mouse red blood cells (BrMRBC) or T cell surface antigens was examined in autoimmune and normal mice. This was accomplished by fixing target cells to microtiter plates such that their membrane antigens could be detected in ELISA and ELISA-spot assays. This technique was rapid, sensitive, and permitted antibodies of both the IgG and IgM isotypes to be measured independently. Autoimmune NZB, BXSB male and MRL-lpr/lpr mice had 10-100-fold higher levels of serum anti-BrMRBC and anti-T cell antibodies than did control DBA/2 and CBA/J animals. The frequency of splenic B cells producing autoantibodies of these specificities was similarly increased among autoimmune mice. In general, the number of antibody-forming cells (AFC) reactive with BrMRBCs was 2-5 times higher than the number reactive with T cell surface determinants. In NZB mice these cells produced primarily IgM autoantibodies whereas in MRL-lpr/lpr animals they secreted primarily IgG. The concentration of serum autoantibody did not precisely correlate with AFC frequency, indicating that immunoglobulin catabolism and other factors play a role in regulating serum antibody concentration.

Spontaneous IgA synthesis by blood mononuclear cells in alcoholic liver disease

Changes in the concentration and composition of serum immunoglobulin A (IgA) and deposits of IgA in tissues are well-known characteristics of alcoholic liver disease. We investigated whether these changes also accompany IgA synthesis by peripheral blood mononuclear cells (MNC), by counting immunoglobulin-producing cells using a solid-phase enzymatic 'spot' test, and by analysis of immunoglobulin content in lysed cells with culture supernatant using conventional enzymatic methods. Patients with alcoholic liver disease exhibited a significantly higher number of spontaneously IgA-producing cells than did normal healthy controls (1.7 X 10(6) cells/blood and 0.5 X 10(6) cells/blood, respectively, P less than 0.01). The IgA content of MNC directly after isolation was also higher (38 and 13 ng/10(6) MNC, respectively, P less than 0.01), as was the IgA production during an unstimulated 6-day culture period (520 and 95 ng/10(6) MNC put into culture, respectively, P less than 0.001). The spontaneously IgA-producing cells assessed directly after isolation of mononuclear cells correlated with the IgA production during an unstimulated culture (P less than 0.01). We conclude that in alcoholic liver disease, B lymphocytes circulate which may have been activated in vivo.

Antigen-specific activation of autoreactive B cells in normal human individuals

The purpose of our study was to determine if normal human B cells can be activated to autoantibody production using an antigen-specific system. For this purpose we investigated the in vitro antibody response to the autoantigen thyroglobulin (Tg) employing soluble or insolubilized Tg (i-Tg) and a B cell growth and differentiation factor (BDGF) to stimulate lymphocytes from healthy individuals. Similar experiments were carried out with the xenoantigen ovalbumin (OVA). The presence of Tg and OVA-reactive B cells was demonstrable by stimulating lymphocytes from tonsil, spleen and blood with a combination of pokeweed mitogen and formalinized Staphylococcus aureus: mitogen stimulation resulted in the generation of IgM anti-Tg and IgM anti-OVA antibody-forming cells (AFC) as detected in a spot enzyme-linked immunosorbent assay. Soluble antigen failed to induce autoantibody production. However, i-Tg or i-OVA did activate normal tonsil and spleen B cells. Differentiation of these activated B cells to IgM AFC required the presence of BGDF, derived from a human T hybrid clone. Preincubation experiments with the particulate autoantigen show that a specific activation signal is provided by the antigen which subsequently renders the B cells responsive to BGDF. i-Tg-dependent stimulation of B lymphocytes could be inhibited by adding free Tg to the cultures; the same applied to i-OVA stimulation. We conclude that the normal human B cell repertoire contains B cells that can be activated to autoantibody production by the autoantigen Tg if the necessary T cell signals are provided. Thus, these B cells are not in an inherently anergic state. Similar mechanisms seem to play a role in the activation of B cells responding to i-OVA and i-Tg.