Substantially increased sensitivity of the spot-ELISA for the detection of anti-insulin antibody-secreting cells using a capture antibody and enzyme-conjugated insulin

Immune protection of human milk

Human milk contains a very large number of specific and non-specific immunologic and nonimmunologic factors who provide passive and active protection to the newborn. The immunologic factors are either immunostimulatory or immunosuppressive. The immunostimulatory ones increase host defense mechanisms mainly against infective illness, and the immunosuppressive ones downregulate inflammation and the development of allergies. Furthermore, human milk has been found to promote intestinal growth and maturation and to have immunomodulating effects beyond infancy, later on in life. In conclusion, human milk represents a very valuable weapon for enhancing the immature immunologic system of the newborn and for strengthening its deficient host defense mechanisms against infective or other foreign agents.

Multivalent cross-linking of membrane Ig sensitizes murine B cells to a broader spectrum of CpG-containing oligodeoxynucleotide motifs, including their methylated counterparts, for stimulation of proliferation and Ig secretion

We have previously reported that B cells that are activated by multivalent but not bivalent membrane Ig cross-linking ligands synergize with various B cell activators culminating in enhanced B cell proliferation. In this study we asked whether B cells that are activated by a multivalent mIg cross-linking agonist could respond to oligodeoxynucleotides (ODN) containing non-stimulatory motifs. Earlier reports have shown that ODN containing a CpG motif in which the cytosine is unmethylated and is flanked by two 5' purines and two 3' pyrimidines induce high levels of B cell activation, while ODN whose CpG are methylated or flanked by sequences other than the optimal two 5' purines and two 3' pyrimidines were non-stimulatory. In this manuscript we show that when B cells are stimulated in vitro with dextran-conjugated anti-IgD antibodies (anti-IgD-dex), as the multivalent mIg ligand, their proliferation is enhanced and they can be induced to secrete Ig in response to ODN containing various non-optimal motifs, both methylated and non-methylated. Furthermore we could induce synergistic levels of proliferation with concentrations of anti-IgD-dex that were in the picomolar concentration range and with concentrations of ODN that were 10- to 100-fold less than previously reported to be necessary for mitogenic activity. These data provided a model to explain how low concentrations of a multi-epitope-expressing microorganism in the context of mammalian (methylated) or microorganism (non-methylated) DNA can lead to dysregulated B cell proliferation and Ig secretion.

Heterogeneity in the ability of cytotoxic murine NK cell clones to enhance Ig secretion in vitro

We recently described a panel of cytotoxic murine NK cell clones that also enhanced Ig secretion by B cells activated in an in vitro model of T cell-independent type 2 (TI-2) responses. We employed dextran-conjugated anti-IgD (alphadelta-dex) as a model antigen. Here we study the mechanism of Ig induction by these clones. Addition of the various NK clones to sort-purified B cells stimulated with alphadelta-dex and IL-2 resulted in a markedly heterogeneous increase in Ig secretion, which varied from 3-fold, as mediated by clone PKO 56, to 15-fold, as induced by clone PKO 101. The other NK cells showed intermediate levels of Ig induction. Furthermore, while addition of as few as 0.04% of PKO 101 cells stimulated significant increases and 1% induced near maximum Ig production, a 3% addition of PKO 56 cells was required for significant enhancement of Ig secretion. Supernatant material collected from the NK clones mediated Ig production at levels that mirrored the induction by the corresponding cells. Cytokine analysis showed that while all members of the NK panel produced IFN-gamma only two secreted granulocyte macrophage colony stimulating factor and that the levels of Ig induction mediated by the NK clones correlated only with their levels of IFN-gamma secretion. Culture of B and NK cells in the presence of anti-IFN-gamma demonstrated that IFN-gamma was the critical cytokine in NK-induced Ig production. These findings establish heterogeneity in the ability of NK cells to increase Ig secretion in vitro and show that NK-produced IFN-gamma is an important factor in determining this heterogeneity.

Kinetics and cross-reactivity of the virus-specific antibody-forming cells in mice during primary and secondary infection with Japanese encephalitis virus and related flaviviruses

A modified antibody-forming cell assay was used to enumerate splenocytes secreting antibodies to Japanese encephalitis (JE) virus and four other flaviviruses in infected cells as the target antigens. The optimal viral antigen expression for the assay was standardized in the infected cells for each virus and the incubation time varied depending of the cell line and the virus. The kinetics of response of JE virus-infected mice readily showed IgG isotype switching. Antibody-forming splenocytes of mice primed or boosted with one flavivirus could distinguish, in variable proportions, the homologous virus antigen from heterologous ones depending on the serocomplex of the virus. Antibody-forming cells from flavivirus-infected mice were flavivirus specific as evidenced by the lack of recognition of Getah virus (alphavirus) antigen. After JE virus-infected mice were cross-primed with another flavivirus, the IgG-forming cell response resembled the secondary response to both viruses but had higher affinity to JE virus than to the cross-priming virus.

Improved sensitivity in the antibody-forming cell assay for Japanese encephalitis virus in mice by optimal fixation of cells and avidin-biotin complex (ABC) immunocytochemistry

A sensitive modified method for the detection in vitro of antibody-forming cells (AFCs) in Japanese encephalitis (JE) virus infected mice is described. The procedure involves the selection of the most appropriate incubation period, after the infection of monolayer cells, for expression of viral antigens to be recognized by AFCs. Adequate preservation of the expressed antigens was achieved after fixation with paraformaldehyde-lysine-periodate buffer (PLP). The development of spots which corresponded to AFCs was successfully obtained with the use of the avidin-biotin complex (ABC) amplification reaction. The number of the spots developing after completion of the assay was greater after PLP fixation compared with other fixation solutions such as methanol, formalin and acetone-water. Optimum antigen expression on the infected cells for recognition by lymphoid cells was reached after 24 h of infection. However, it was possible to detect viral antigens on the infected cells 8 h after infection. The ABC reaction was shown to be the best procedure for developing spots compared with other immunocytochemical methods. A linear increment was observed in the number of spots that developed at different spleen cell densities. This assay is simple to perform and could detect virus-specific Ig producing cells from the spleens of mice infected with JE virus. It also makes it possible to enumerate accurately the kinetics of the AFC response in different lymphoid organs during infection or after vaccination.

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.

Synthetic peptide conjugates with horseradish peroxidase and beta-galactosidase for use in epitope-specific immunocytochemistry and ELISA

Synthetic peptide-alkaline phosphatase conjugates can be used to detect the epitope specificity of (i) antibody-forming cells in vivo by immunocytochemistry; (ii) of antibody secreting cells in vitro by spot-ELISA; and (iii) antibodies in solution by capture ELISA. The availability of synthetic peptide-enzyme conjugates using detector enzymes other than alkaline phosphatase would offer several important advantages, for example in double staining approaches. This paper reports the production of synthetic peptide-horseradish peroxidase conjugates and synthetic peptide-beta-galactosidase conjugates. A peptide of 21 amino acids (SP 29) was coupled to peroxidase in seven differing molar ratios of peptide over peroxidase, ranging from 1:3.4 to 1:575, using periodate oxidation of the enzyme. SP 29 was coupled to beta-galactosidase in four molar ratios ranging from 1.25 to 10, using glutaraldehyde pre-activation of the enzyme. The enzyme activity of the different conjugates was determined, the conjugates were tested in direct capture-ELISA with peptide-specific monoclonal antibodies, and the conjugates were tested in immunocytochemistry to detect peptide-specific B cells. The results show that the conjugates perform best if the peptide is coupled to the enzyme at relatively low molar ratios (1-30). The availability of these new peptide-enzyme conjugates broadens the applicability of synthetic peptides for detection purposes in several assay systems.