A small variance in the antigenicity but not function of recombinant β-lactoglobulin purified from the culture supernatant of transformed yeast cells

We purified recombinant bovine β-lactoglobulin (rβ-LG) from the culture supernatant of transformed yeast and investigated whether rβ-LG maintained the functional ability and antigenicity of native β-LG. Immunostaining following gel electrophoresis and reversed-phase high-performance liquid chromatography confirmed that rβ-LG was purified homogeneously. rβ-LG showed almost the same retinol-binding ability as native β-LG purified from bovine milk. However, affinities of two anti-β-LG monoclonal antibodies (mAbs) to rβ-LG were different from those to native β-LG, although three other mAbs bound these two proteins equally. Since our panel of five mAbs has been previously shown to be able to detect structural changes occurring in β-LG, this variance in antigenicity can be attributed to conformational differences between rβ-LG and native β-LG. Then, we studied which step in the production and purification procedure was responsible for altering the antigenicity of rβ-LG. Bovine milk native β-LG was added to several steps in this procedure and purified in the same manner as rβ-LG. The results suggested that incubation in the yeast culture had adverse effects on maintaining the antigenicity of this recombinant protein. We conclude from these results that even if no difference between the native and recombinant proteins can be detected by functional analysis, some subtle conformational change which can be distinguished by mAbs may be incorporated into the recombinant protein during its production and ultimately cause a different immune reaction in vivo.Abbreviations β-LG, β-lactoglobulin; rβ-LG, recombinant β-LG; PBS, phosphate-buffered saline; PBS-Tween, PBS containing 0.05% Tween 20; ELISA, enzyme-linked immunosorbent assay.

Th2 polarization enhanced by oral administration of higher doses of antigen

Although oral administration of a soluble proteinantigen can induce various immune responses, theeffect of the dosage of oral antigen on thepredominance of Th2-type cytokine and antibodyresponses has not been well clarified yet. In thepresent study, we fed T cell receptor (TCR) transgenic(tg) mice various amounts of chicken ovalbumin (0.1,5, and 250 mg) and examined the resulting immuneresponses to this antigen. In these TCR tg mice, theresponses of antigen-specific T cells were greatlyamplified concomitantly with significantantigen-specific cytokine secretion. We found that ahigh dose (250 mg) of antigen significantlyupregulated the serum antigen-specific IgG1 and IgAantibody responses in mice later intraperitoneallyinjected with antigen plus adjuvant. The miceadministered the same oral dose but not immunizedshowed upregulation of Th2-type IL-4 and IL-5secretion and downregulation of Th1-type IL-2 andIFN-gamma. This enhancement of Th2-type cytokineand antibody responses was more marked when largerdoses of antigen orally administered. These resultsdemonstrated that antigen feeding induces thedevelopment of T cells secreting Th2-type cytokines ina dose-dependent manner and that these T cells have ahelper function for the production of antibodies ofthe Th2-type isotypes. This experimental system shouldbe useful to screen foods and other substances thatcan modulate Th2-type responses relating to allergy.

Suppression of collagen-induced arthritis in DBA/1J mice by preimmunization with house dust mite extract

Collagen-induced arthritis (CIA) can be induced in DBA/1J mice by immunization with bovine type II collagen (bCII) and is a model of some types of human autoimmune rheumatoid arthritis. In this study we examined whether preimmunization of the mice with various antigens could inhibit the development of CIA. Preimmunization of the mice with an extract of the house dust mite Dermatophagoides farinae (mite antigen), chicken ovalbumin, or keyhole limpet hemocyanin strongly inhibited CIA development, but hen egg lysozyme, beta-lactoglobulin from bovine milk or myelin basic protein from guinea pig brain did not substantially affect CIA development. Splenic T cells and serum antibodies specific for mite antigen did not cross-react with bCII. Preimmunization of the mice with mite antigen did not affect the IFN-gamma and proliferative response of splenic T cells to bCII, nor serum antibody responses. The most inhibitory constituent had a molecular weight between 1,000 and 10,000.

Improved growth and viability of lactobacilli in the presence of Bacillus subtilis (natto), catalase, or subtilisin

In an effort to demonstrate the potential usefulness of Bacillus subtilis (natto) as a probiotic, we examined the effect of this organism on the growth of three strains of lactobacilli co-cultured aerobically in vitro. Addition of B. subtilis (natto) to the culture medium resulted in an increase in the number of viable cells of all lactobacilli tested. Since B. subtilis (natto) can produce catalase, which has been reported to exhibit a similar growth-promoting effect on lactobacilli, we also examined the effect of bovine catalase on the growth of Lactobacillus reuteri JCM 1112 and L. acidophilus JCM 1132. Both catalase and B. subtilis (natto) enhanced the growth of L. reuteri JCM 1112, whereas B. subtilis (natto) but not catalase enhanced the growth of L. acidophilus JCM 1132. In a medium containing 0.1 mM hydrogen peroxide, its toxic effect on L. reuteri JCM 1112 was abolished by catalase or B. subtilis (natto). In addition, a serine protease from B. licheniformis, subtilisin, improved the growth and viability of L. reuteri JCM 1112 and L. acidophilus JCM 1132 in the absence of hydrogen peroxide. These results indicate that B. subtilis (natto) enhances the growth and (or) viability of lactobacilli, possibly through production of catalase and subtilisin.

Cutting edge: introduction of an endopeptidase cleavage motif into a determinant flanking region of hen egg lysozyme results in enhanced T cell determinant display

The choice of which determinants of a whole Ag will be presented on cell surface MHC class II molecules after uptake and processing by APC is the result of the interplay between structural characteristics of the Ag and the processing machinery of the APC. In this study, we demonstrate that introduction of a dibasic motif adjacent to a subdominant determinant enhances the presentation of this determinant from the whole molecule. This is the first report showing that a single amino acid substitution in a whole Ag, designed to introduce an endopeptidase recognition site, enhances display of class II-restricted determinants, most likely by creating a peptide chain cleavage in the antigenic molecule. Our findings have important implications for the understanding of immunodominance and for vaccine design.

Serum IgE response to orally ingested antigen: a novel IgE response model with allergen-specific T-cell receptor transgenic mice

BACKGROUND

The mechanism by which orally ingested allergens elicit an IgE response remains unclear because there are few animal models available for investigation of this response.

OBJECTIVE

We tried to develop a murine model suitable for investigation of the IgE response to orally ingested allergens, which would allow us to identify T cells that could promote IgE production.

METHODS

Ovalbumin (OVA)-specific T-cell receptor transgenic mice were fed a diet containing OVA, and both the serum antibody response and cytokine production by splenocytes were examined.

RESULTS

Oral administration of OVA to transgenic mice led to an increase in the levels of both antigen-specific IgE and total IgE in the sera. Subsequent intravenous challenge of OVA-fed transgenic mice with OVA resulted in anaphylactic shock. Analysis of cytokine production by splenocytes revealed that high IL-4-producing T cells appeared in the spleen 1 week after the start of feeding the OVA diet. T cells from these mice were found to promote IgE secretion by BALB/c B cells in vitro. This helper activity and the levels of IL-4 secretion were diminished after long-term feeding. These findings suggest the possibility that the orally ingested antigen elicited a response by a subpopulation of T cells that produce high levels of T(H2)-type cytokines and that promote IgE secretion, and these same T cells were tolerized by the orally ingested antigen.

CONCLUSION

This experimental model with transgenic mice may be a useful tool for further studies of the cellular and molecular mechanisms of the T-cell and IgE responses to orally ingested antigens.

Down-regulation of antigen-specific antibody production by TCR antagonist peptides in vivo

The efficacy of TCR antagonist peptides in inhibition of antigen-specific antibody production and T cell responses in vivo was evaluated. Among amino acid-substituted analogs of a peptide corresponding to residues 119 - 133 of bovine beta-lactoglobulin (p119 - 133), pR124Q and pD129S, prepared by substitution of Gln and Ser for Arg(124) and Asp(129), respectively, have been shown to display TCR antagonist activity for three out of four distinct p119 - 133-specific T cell clones and for polyclonal T cells derived from p119 - 133-immunized C57BL / 6 mice. Both pD129S and pR124Q inhibited in vivo priming and subsequent activation of T cells by p119 - 133 when co-injected with p119 - 133 into mice, as shown by the decreased proliferation of T cells in response to p119-133 in vitro. pD129S significantly inhibited production of anti-p119 - 113 antibodies of IgG1, IgG2b and IgE isotype in vivo when co-injected into mice together with p119 - 133 at the time of the first immunization. However, pR124Q was totally ineffective in inhibition of the antibody responses. Anti-p119 - 133 antibodies from p119 - 133-immunized mice could bind to pR124Q but not to pD129S, suggesting that the difference in cross-reactivity is responsible for the different effect of these two peptides on specific antibody production. Our findings demonstrate that a single TCR antagonist peptide can inhibit antigen-specific polyclonal antibody production when this antagonist peptide does not cross-react with the antibody elicited in response to an antigenic peptide.

Primary response of naive CD4(+) T cells to amino acid-substituted analogs of an antigenic peptide can show distinct activation patterns: Th1- and Th2-type cytokine secretion, and helper activity for antibody production without apparent cytokine secretion

Naive CD4(+) T cells differentiate into two types of helper T cells showing an interferon-gamma-predominant (Th1) or an interleukin-4-predominant (Th2) cytokine secretion profile after repeated antigenic stimulation. Their differentiation can be influenced by slight differences in the interaction between the T cell receptor (TCR) and its ligand at the time of primary activation. However, the primary response of freshly isolated naive CD4(+) T cells to altered TCR ligands is still unclear. Here, we investigated the primary response of splenic naive CD4(+) T cells derived from transgenic mice expressing TCR specific for residues 323-339 of ovalbumin (OVA323-339) bound to I-A(d) molecules. Naive CD4(+) T cells secreted either Th1- or Th2-type cytokines immediately after stimulation with OVA323-339 or its single amino acid-substituted analogs. Helper activity for antibody secretion by co-cultured resting B cells was also found in the primary response, accompanied by either low-level Th2-type cytokine secretion or no apparent cytokine secretion. Our results clearly indicate that dichotomy of the Th1/Th2 cytokine secretion profile can be elicited upon primary activation of naive CD4(+) T cells. We also demonstrate that the helper activity of naive CD4(+) T cells for antibody production does not correspond to the amounts of the relevant cytokines secreted.

The self-directed T cell repertoire against mouse lysozyme reflects the influence of the hierarchy of its own determinants and can be engaged by a foreign lysozyme

The T cell repertoire is shaped by the processes of positive and negative selection. We have previously shown that mice are tolerant to a native self-Ag, mouse lysozyme (ML), but they respond vigorously when challenged with different ML peptides ("cryptic" self-determinants). In this study, we have addressed the issue of the physiological significance of both the hierarchy (dominance/crypticity) of self-determinants within ML and the anti-cryptic, self (ML)-directed T cell repertoire. Our results demonstrate that there are several ML peptides that bind well to MHC but are totally nonimmunogenic when tested for proliferative T cell response and cytokine secretion: a subset of these peptides presumably represent the originally dominant self-determinants of ML, which have rendered the T cells tolerant during thymic selection. Other ML peptides, which bind well to MHC and are immunogenic, correspond to the cryptic determinants of ML: T cells against cryptic ML determinants escape tolerance induction. Thus, the mature T cell repertoire against ML bears the direct imprint of the hierarchy of self (ML)-determinants. Interestingly, hen egg white lysozyme could prime T cells in vivo that were cross-reactive with certain cryptic ML determinants, and vice versa, without requiring any coimmunization with the foreign lysozyme and ML peptide(s). Moreover, repeated, deliberate priming and expansion of T cells by hen egg white lysozyme immunization concomitantly enhanced T cell response to such cross-reactive ML determinants. This reciprocal self-foreign determinant cross-reactivity may play a previously unrecognized, but crucial, role in the expansion and diversification of self-reactive clones in the autoimmune response.

Accelerated secretion of mutant beta-lactoglobulin in Saccharomyces cerevisiae resulting from a single amino acid substitution

Transformed yeasts producing a mutant form of bovine beta-lactoglobulin (beta-LG), W19Y, in which Trp(19) was replaced with Tyr, were shown to secrete 6 times more than those producing wild type beta-LG. Northern blot analysis suggested that the enhanced level of secretion was not the result of upregulated transcription of W19Y. The ratio of the amount of W19Y secreted into the supernatant to the amount of W19Y remaining inside the cells was much larger than that in the case of wild type beta-LG as shown by immunoblot analysis. A pulse/chase experiment revealed that the speed of secretion of W19Y was significantly accelerated, compared to wild type beta-LG. These results indicated that W19Y was more efficiently and rapidly transported in the course of secretion than wild type beta-LG. Our previous study showed that the DeltaG of unfolding of W19Y in water is 6.9 kcal/mol smaller than that of wild type beta-LG. Furthermore, immunoblot analysis of intracellular beta-LG under non-reducing conditions indicated that W19Y as well as wild type beta-LG maintained a specific folded structure inside the yeast cells, whereas other non-secretable mutant beta-LGs with Phe or Ala at position 19 (W19F and W19A, respectively) did not. These data suggest that low molecular stability and the maintenance of a specific folded structure inside the yeast cells are prerequisites for efficient and rapid secretion. W19Y was more efficiently secreted than wild type beta-LG also in transformed ern1 mutant yeast cells expressing only a basal level of BiP which is considered to function in quality control in the endoplasmic reticulum (ER) by playing an important role in determining the secretion efficiency of secretory proteins. Thus, the reason for the enhanced secretion of W19Y is considered to be that the improved folding ability of W19Y can allow the half-life of the W19Y-BiP complex to become shorter than that of the wild type beta-LG-BiP complex, leading to faster translocation of W19Y into transport vesicles, or that W19Y can fold in a BiP-independent manner in the ER of the yeast cells. Our findings demonstrate that the amount of protein secreted can be improved by alteration of a single amino acid residue crucial for its structure.

Autocrine B-cell stimulation by interleukin-2 during a cognate interaction with T-cells

Interleukin-2 (IL-2) secretion as well as expression of IL-2 receptor has been demonstrated for B-cells in response to several activating stimuli. However, the exact role of B-cell-derived IL-2 in the T-cell-dependent antibody response remains to be determined. Here, we have examined the autocrine regulatory roles of IL-2 secreted from B-cells. Splenic resting B-cells were stimulated with a fixed pre-activated Th1 clone, G1.19, in the presence of a single amino acid-substituted peptide (pD129A; Ala-129 substituted for Asp-129), an analog of the original ligand (p119-133, derived from bovine beta-lactoglobulin) recognized by G1.19 cells. pD129A allowed a cognate interaction between B-cells and fixed pre-activated G1.19 T-cells, but pD129A had no agonistic activity against G1.19 T-cells. Thus, the level of expression of B-cell-activating molecules on T-cells remained unchanged after stimulation with pD129A. Regardless of the lack of ability to induce IL-2 secretion in the case of T-cells, pD129A significantly enhanced antibody secretion from B-cells, and this was partially blocked by anti-IL-2 antibody. Furthermore, IL-2 secretion from B-cells was modestly upregulated in response to added pD129A. Taken together, these data suggest that helper signals from interacting cognate T-cells induce IL-2 secretion by B-cells, which can enhance antibody secretion in an autocrine manner.

Changes in fecal microflora induced by intubation of mice with Bacillus subtilis (natto) spores are dependent upon dietary components

We examined changes in mouse fecal microflora after various dietary components and Bacillus subtilis (natto) spores were delivered by intubation. The administration of intact spores of Bacillus subtilis (natto) did not affect fecal Enterobacteriaceae and Enterococcus spp. in all three diet groups; on the other hand, it did affect fecal Bacteroidaceae and Lactobacillus spp., depending upon the diets fed. The administration of autoclaved spores did not alter fecal microflora. In vitro cultures of Lactobacillus murinus obtained from mouse feces, together with Bacillus subtilis (natto) under aerobic conditions as a mixed culture, revealed that the growth of L. murinus was enhanced by the addition of intact spores of Bacillus subtilis (natto). This enhancement of growth was displayed only in media containing either sucrose, glucose, maltose, or fructose but not in media containing cornstarch, soluble starch, or microcrystalline cellulose. From these results it was evident that some metabolites of Bacillus subtilis (natto) produced during germination and (or) outgrowth of spores of this strain, requiring monosaccharides or oligosaccharides, participated in the enhancement of the growth of L. murinus.

Anti-DNA IgA autoantibodies are spontaneously generated in mouse Peyer's patches

IgA antibodies in the mucosal immune system are produced specifically to environmental antigens such as virus and bacteria, and possibly to some food components, which will provide a potential luminal antigen, DNA. To study the immune response to DNA in the gut, we established B-cell hybridomas producing IgA monoclonal antibodies (mAb) from Peyer's patches (PP) of non-immunized, non-autoimmune, specific pathogen-free BALB/c mice, and examined their specificity by enzyme-linked immunosorbent assay (ELISA). Three mAb out of 18 bound strongly to self, bacterial and synthetic DNA, with Kd of about 10-7 m. One of the three mAb also reacted with the histone component and another reacted with some mouse food component. The VH genes of these three mAb have not previously been reported to have anti-DNA specificity, and carry putative somatically mutated sites favouring DNA binding in CDR. The features resemble those of anti-DNA antibodies found in human and murine models of systemic lupus erythmatosus (SLE), and are indicative of an antigen-driven selection process. Our findings suggest that even in normal healthy animals, anti-DNA antibodies of IgA isotype can be produced in certain peripheral environments such as in PP by spontaneous antigenic stimulation.

Intranasal administration of denatured type II collagen and its fragments can delay the onset of collagen-induced arthritis

Collagen-induced arthritis (CIA) is an autoimmune animal model for some types of human rheumatoid arthritis (RA). We have evaluated the effectiveness of intranasal administration of antigen in inhibiting CIA in DBA/1 mice. The intranasal administration of heat-denatured or trypsin-digested bovine type II collagen (CII) before immunization with CII strongly delayed the onset of CIA, whereas administration of native CII did not do so. The mice administered denatured or digested CII possessed much lower titers of anti-CII IgG2a than the control mice, whereas titers of anti-CII IgG1 and IgG2b were unchanged or slightly decreased. Responding to CII and peptides containing immunodominant T cell determinants, lymph node cells from mice administered denatured CII produced less IFN-gamma. These results suggest that intranasal administration of antigen downregulated preferentially Th1-type responses, whereas an enhanced Th2-type response was not observed. We demonstrate that the methods shown here are a possible treatment for rheumatoid arthritis.

Determinant analysis of IgE and IgG4 antibodies and T cells specific for bovine alpha(s)1-casein from the same patients allergic to cow's milk: existence of alpha(s)1-casein-specific B cells and T cells characteristic in cow's-milk allergy

In an effort to clarify the etiology of milk allergy from the standpoint of allergen-specific immune reactions, we investigated the determinants of IgE, IgG4, and T cells specific for bovine alpha(s)1-casein from the same individual patients by using its synthetic peptides and cyanogen bromide-digested fragments. Alpha(s)1-casein is a major allergen in cow's milk, and its unique conformation enabled us to investigate the determinants of antibodies without consideration about missing the reactivities because of conformational changes. Nine patients were selected as subjects from among 129 milk-sensitive infants screened by ELISA to assess the anti-alpha(s)1-casein IgE levels in their sera. By using ELISA for epitope mapping, a C-terminal region of alpha(s)1-casein was identified as a common binding site for IgE from all of these patients, whereas those for anti-alpha(s)1-casein IgG4 were located in multiple regions of alpha(s)1-casein. We determined the specificities of seven alpha(s)1-casein-specific T-cell lines established from peripheral blood mononuclear cells of two of the patients. These T cells have been shown to secrete IL-4. All of the T-cell lines had different specificities to alpha(s)1-casein. However, a common amino acid residue use was found among the determinants of various T-cell lines from each patient. The results suggest that patients allergic to cow's milk have characteristic B cells recognizing a limited region of alpha(s)1-casein and secreting alpha(s)1-casein-specific IgE. These B cells may interact particularly with T cells recognizing determinants with a common structure.

MHC class II/T-cell receptor interactions potentiate secretion of IgG but not IgM in response to T-dependent antigens

We have examined whether the interaction of peptide-loaded MHC molecules on the surface of B-cells with antigen-specific T-cell receptors (TCRs) enhances Ig secretion in the presence of other antigen-independent interactions in vitro. B-cells specific for region 25-40 of beta-lactoglobulin (beta-LG) were stimulated in a T-cell dependent manner using plasma membranes (PM) derived from two different T-helper (Th) clones, culture supernatants of activated Th2 cells and beta-LG as a specific antigen. PM were obtained from either the beta-LG-specific T-cell clone H1.1 which can mediate specific TCR/MHC class II interactions as well as antigen-independent ones or from the D10 clone which bears a TCR of an irrelevant specificity and thus, can only mediate antigen-independent interactions. IgG, but not IgM, secretion was specifically enhanced by H1.1 PM, but not D10 PM in the presence of beta-LG. Furthermore, a blockade of TCR/MHC class II interactions using either anti-T-cell receptor, beta or anti-CD4 monoclonal antibodies inhibited this enhanced IgG secretion in response to beta-LG. The results show that while antigen-independent interactions between T- and B-cells can enhance secretion of IgM antibodies, specific interactions between TCRs and peptide:MHC complexes stimulate B-cells to enhance secretion of IgG but not IgM antibodies. This mechanism may contribute to antibody secretion only from B-cells activated through cognate interaction in vivo.

Lactobacillus casei inhibits antigen-induced IgE secretion through regulation of cytokine production in murine splenocyte cultures

BACKGROUND

Lactobacillus casei is a nonpathogenic gram-positive bacterium widely used in dairy products and has been shown to enhance the cellular immunity of the host.

METHODS

To examine the inhibitory effect of L. casei on IgE production, splenocytes obtained from ovalbumin (OVA)-primed BALB/c mice were restimulated in vitro with the same antigen in the presence of heat-killed L. casei. The effect of this bacterium on T helper (Th) phenotype development was also examined with naive T cells from OVA-specific T cell receptor-transgenic mice.

RESULTS

L. casei induced IFN-gamma, but inhibited IL-4 and IL-5 secretion, and markedly suppressed total and antigen-specific IgE secretion by OVA-stimulated splenocytes. The inhibitory effect of L. casei on IgE, IL-4, and IL-5 production was partially abrogated by addition of neutralizing antibody to IFN-gamma. Augmented IL-12 production was also observed in the cell cultures containing L. casei, and anti-IL-12 monoclonal antibody completely restored the IgE, IL-4, and IL-5 production to the control levels. The IL-12 augmentation by L. casei was macrophage-dependent. The Th cell development assay showed the ability of L. casei to induce Th1 development preferentially. This effect was also completely blocked by anti-IL-12 antibody.

CONCLUSIONS

This is the first demonstration that a nonpathogenic microorganism, L. casei, can inhibit antigen-induced IgE production through induction of IL-12 secretion by macrophages. The findings suggest a potential use of this organism in preventing IgE-mediated allergy.

Characterization of a water-soluble polysaccharide fraction with immunopotentiating activity from Bifidobacterium adolescentis M101-4

The soluble and insoluble fractions obtained after sonication and centrifugation of Bifidobacterium adolescentis M101-4 cells were examined, and both of these fractions exhibited mitogenic activity in an assay of murine splenocytes and Peyer's patch cells in vitro. The soluble fraction was further treated by a 6-step procedure involving proteinase K-treatment, ultrafiltration with a 50-kDa cut-off molecular-sieving membrane, anion-exchange chromatography, dialysis, ultrafiltration through a 6-kDa cut-off membrane filter, and gel-filtration to yield a soluble high molecular weight fraction (SHF) which was effective for stimulating the proliferation of murine splenocytes. Almost three quarters of this fraction by weight was found to consist of carbohydrates containing glucose and galactose as major constituents, and the average molecular weight was estimated to be between 60,000 and 2,460,000, with the main peak at 1,550,000 Da, by the retention time of gel permeation chromatography. A structural analysis by 1H- and 13C-nuclear magnetic resonance and methylation indicated that SHF contained polysaccharides consisting of -4Galp1-, -4Glcp1-, and -6Glcp1- as the major residues, and Galf1- and -6Galf1- as the minor residues. Immunopotentiating SHF was found to contain galactofuranosyl residues as characteristic constituents which had not been previously detected in other soluble fractions from Gram-positive bacteria.

Antigen-specific inhibition of CD4+ T-cell responses to beta-lactoglobulin by its single amino acid-substituted mutant form through T-cell receptor antagonism

T-cell responses can be antagonized by some single amino acid-substituted analogs of a peptide ligand for T-cell receptors (TCR), and these are called TCR antagonists. In this study, we addressed the question of whether TCR antagonism can be elicited by a whole protein antigen carrying a mutated T-cell determinant region corresponding to a TCR antagonist peptide. To clarify this, we examined the ability of a single amino acid-substituted mutant form of bovine beta-lactoglobulin (beta-Lg) to inhibit three CD4+ T-cell clones recognizing a peptide corresponding to an immunodominant determinant region 119-133 of beta-Lg (p119-133). First, we identified pD129A, an analog of p119-133 with a substitution of Ala for 129Asp, as an antagonist which can inhibit the response of two of the three T-cell clones. Then, using a yeast expression system, we prepared a mutant beta-Lg (mutD129A) with the same substitution of Ala for 129Asp as that in pD129A. This mutant protein could inhibit the proliferation of the two T-cell clones in a manner similar to the effect of pD129A. From these results we can demonstrate that TCR antagonism can be elicited by peptides naturally processed from a single-substituted mutant protein as well as by the corresponding peptides added exogenously.

Fine mapping of T-cell determinants of bovine beta-lactoglobulin

T-cell recognition sites, i.e. T-cell determinants, of bovine beta-lactoglobulin, a major allergen in milk, were analyzed in detail. For this purpose, we prepared primary cultures of lymph node cells from three strains of mice, C57BL/6 (H-2b), C3H/HeN (H-2k), and BALB/c (H-2d), and examined the proliferative response of these cells to a complete set of overlapping 15-mer peptides which covered the entire sequence of beta-lactoglobulin by shifting in single amino acid steps. We were able to determine the putative core sequence of each T-cell determinant and estimate its relative importance. In the case of C57BL/6 mice, dominant, subdominant, and minor determinants were identified as residues 122-130, 16-26, and 108-122, respectively, as represented by their core sequences. Each determinant peptide induced the production of interferon-gamma, the amount of which showed a correlation with the intensity of the proliferative response induced by each determinant. In the case of C3H/HeN mice, a dominant determinant comprised of residues 140-148 was identified together with three subdominant and two minor determinants. Dominant T-cell determinants recognized in BALB/c mice were identified as residues 67-75, 71-79, and 80-88, and six other regions were identified as subdominant determinants. Comparisons between our results and the determinants predicted from relevant MHC-binding motifs reported to date revealed the inadequacy of the motifs in predicting even the dominant determinants. The information obtained by complete mapping of T-cell determinants as done in this study is expected to be helpful in establishment and evaluation of new prediction methods and also may contribute to the development of a new approach to control immune responses by manipulation of the T-cell determinants of allergens.

In vivo macrophage-stimulation activity of the enzyme-degraded water-soluble polysaccharide fraction from a marine alga (Gracilaria verrucosa)

The water-soluble polysaccharide fraction from Gracilaria verrucosa (GWS) has been reported to increase the phagocytic activity of mice [Yoshizawa et al., Nippon Shokuhin Kogyo Gakkaishi, 41, 557-560 (1994)]. In this study, the macrophage-stimulation activity of enzyme-degraded GWS (GWS-E) was investigated by intraperitoneally and orally administering GWS-E to mice. The intraperitoneal administration of GWS-E increased the number of peritoneal exudate cells (PEC), and increased the phagocytic activity and oxygen radical-secreting activity (spontaneous chemiluminescence) of PEC. This administration could also stimulate splenic macrophages (SPM), increasing radical-secreting activity. When GWS-E was administered orally, the radical-secreting activity of PEC and SPM increased. In this case of oral administration, the activity of SPM increased in a dose-dependent manner, while that of PEC had an optimum dose. These results indicate that GWS-E had macrophage-stimulation activity in vivo and would be suitable as a source for a physiologically functional food with protective and immunopotentiating activity.

The direct cloning of the immunoglobulin VH genes from primary cultured B cells specific for a short peptide

A new and simple method was devised to obtain immunoglobulin VH genes directly from primary cultured B cells specific for a short peptide. Peptide-specific B cells were separated from splenocytes of peptide-immunized BALB/c mice with antigen-coated magnetic beads, and were cloned by a limitedly diluted culture in the presence of lipopolysaccharide, recombinant interleukin (rIL) -2, rIL-4 and rIL-5, and 3T3 fibroblasts as filler cells for 7 days. Seventeen clones were obtained from 3 x 10(3) fractionated cells by screening the positive wells containing anti-peptide antibody-secreting cells by an enzyme-linked immunosorbent assay (ELISA). The VH cDNAs of these clones were amplified by a set of primers; a primer complementary to the mu-chain constant region gene and the other with high complementarity to most of the VH genes. This is the first report of success in obtaining unknown VH genes directly from primary B cell clones, after their antigen-specificity has been confirmed by ELISA. This new method will provide a powerful tool for designing specific recombinant antibodies.

Establishment and characterization of alpha s1-casein-specific T-cell lines from patients allergic to cow's milk: unexpected higher frequency of CD8+ T-cell lines

To study cow's milk allergy at the cellular level, we assessed the reactivity of peripheral blood mononuclear cells from patients allergic to cow's milk to alpha s1-casein, which is one of the major allergens in cow's milk. Proliferation of the cells to alpha s1-casein activation showed a rather weak response. Therefore to understand T-cell reactivity to alpha s1-casein in more detail, we prepared alpha s1-casein-specific T-cell lines from patients allergic to cow's milk and established 26 T-cell lines. These T-cell lines could be classified into three groups by analyzing their surface marker expression: those containing predominantly CD4+ CD8- T cells, those containing both CD4+CD8- and CD4-CD8+ T cells, and those containing predominantly CD4- CD8+ T cells. The CD8+ T cells were obtained at an unexpectedly higher frequency from the patients. These T-cell lines produced interferon-gamma and IL-4. These results suggest that CD8+ T cells specific for alpha s1-casein and CD4+ T cells were primed by the stimulation with alpha s1-casein in patients allergic to milk and that both T cells may play a key role in the onset, progression of, or recovery from cow's milk allergy.

Antigen processing and T cell repertoires as crucial aleatory features in induction of autoimmunity

Induction of self-reactive T cell responses leading eventually to autoimmune pathology involves several key events: (1) availability of a determinant cross-reactive with the pathogenic self or foreign determinant upon processing of native antigen; the foreign molecule bearing the related determinant may have additional processing sites flanking the determinant, or at least different ones (the same determinant may only be available on the native self molecule under inflammatory conditions) (2) a T cell bearing T cell receptor (TCR) capable of response to the autoantigen; (3) ability of the processed self determinant to bind efficiently to the appropriate major histocompatibility complex (MHC) molecule as well as to interact with the appropriate TCR, coordinated with the absence of competitively dominant determinants; and (4) the lack of regulation. At any step of this cascade of interactions, the conditions could either favour induction of an autoreactive T cell response or the process may be truncated/stalled at any step without any adverse effect. A major component determining the outcome of the above interactions is the aleatory nature of the antigen processing events. Experiments highlighting these aleatory events are the focus of this report.

IL-3 augments TCR-mediated responses of type 2 CD4 T cells

A subset of type 2, but not type 1, CD4 T cell clones expresses IL-3R and can be stimulated by IL-3. Expression of IL-3R on these type 2 T cell clones is induced by TCR stimulation, and subsequent stimulation by IL-3 augmented the proliferation of and IL-4 production by these cells. This augmented response is inhibited by anti-IL-4 mAb, suggesting the involvement of IL-4 in this response. In place of TCR stimulation, treatment of these type 2 CD4 T cell clones with PMA rendered them responsive to further stimulation of proliferation by IL-3, indicating the cooperation between the IL-3R-elicited signals and PKC-mediated signals in stimulating proliferation. Although the augmentation of the TCR-mediated proliferative response by IL-3 was mainly due to the increased production of IL-4, we also demonstrated the presence of IL-4-independent mechanism mediating the response to IL-3. In situ, we found that splenic T cells could be induced to respond to Il-3 by TCR stimulation. Thus, IL-3 can stimulate a specific population of T cells and influence the immune response.

IL-3 augments TCR-mediated responses of type 2 CD4 T cells

A subset of type 2, but not type 1, CD4 T cell clones expresses IL-3R and can be stimulated by IL-3. Expression of IL-3R on these type 2 T cell clones is induced by TCR stimulation, and subsequent stimulation by IL-3 augmented the proliferation of and IL-4 production by these cells. This augmented response is inhibited by anti-IL-4 mAb, suggesting the involvement of IL-4 in this response. In place of TCR stimulation, treatment of these type 2 CD4 T cell clones with PMA rendered them responsive to further stimulation of proliferation by IL-3, indicating the cooperation between the IL-3R-elicited signals and PKC-mediated signals in stimulating proliferation. Although the augmentation of the TCR-mediated proliferative response by IL-3 was mainly due to the increased production of IL-4, we also demonstrated the presence of IL-4-independent mechanism mediating the response to IL-3. In situ, we found that splenic T cells could be induced to respond to Il-3 by TCR stimulation. Thus, IL-3 can stimulate a specific population of T cells and influence the immune response.

Macrophage stimulation activity of the polysaccharide fraction from a marine alga (Porphyra yezoensis): structure-function relationships and improved solubility

The polysaccharide fraction from Porphyra yezoensis (PASF) has already been shown to stimulate murine phagocytic functions in vivo and in vitro [Y. Yoshizawa et al., Biosci. Biotech. Biochem., 57, 1862-1866 (1993)]. In this study, various treatments were applied to PASF to assess its structure-function relationships. Desulfation of PASF decreased in vitro macrophage-stimulation activity, while further sulfation of PASF did not change the activity. Among 7 fractions obtained by anion-exchange chromatography of PASF, stronger activity was found in the fractions having a lower or higher sulfate content than in those having a medium sulfate content. Digests of PASF with beta-agarase showed higher activity and solubility, and lower viscosity, than undigested PASF. These results indicate that the sulfate groups in PASF, probably porphyran, contributed to the macrophage stimulating activity, although a larger number of sulfate groups did not always cause stronger activity.

Differential inhibition of T and B cell responses to individual antigenic determinants in orally tolerized mice

Immunological tolerance of systemic immunity can be induced by the oral administration of an exogenous antigen, which is termed oral tolerance. We examined whether there was a difference in the degree of tolerance between individual antigenic determinants in oral tolerance. Feeding bovine alpha s1-casein, a major protein in cow's milk, as a constituent of the diet induces oral tolerance in mice. However, a weak antibody response can be elicited in the alpha s1-casein-fed animals by subsequent immunization with the antigen. We examined the fine specificity of such anti-alpha s1-casein antibodies produced in alpha s1-casein-fed mice. The results demonstrated that there was a difference in the inhibition of antibody response between different B cell determinants. Differential inhibition could also be observed for T cell responses. T cells specific for dominant determinants were preferentially tolerized, while those for cryptic determinants escaped oral tolerance. Our results imply the importance of antigen presentation for this differential inhibition of antigenic determinants. We suggest that orally administered antigen does not induce tolerance to some of the B and T lymphocyte repertoire which could potentially induce harmful food hypersensitivity.

Tryptophan-19 of beta-lactoglobulin, the only residue completely conserved in the lipocalin superfamily, is not essential for binding retinol, but relevant to stabilizing bound retinol and maintaining its structure

Residue 19 of tryptophan in bovine beta-lactoglobulin (beta-LG) is the only invariant residue throughout the lipocalin superfamily having two characteristic features: binding ability for small hydrophobic molecules and the unique beta-barrel three-dimensional structure. In this study, we investigated whether this strictly conserved Trp-19 of beta-LG would be indispensable for its structure and function such as maintaining the molecular structure and biological activity of beta-LG. Spectroscopic and enzymatic oxidation experiments on retinol bound to W19Y, in which Tyr was substituted for Trp-19, showed that Trp-19 was not critical for this binding, but was important for stably maintaining the environment surrounding retinol and the bound retinol. An using four anti-beta-LG monoclonal antibodies as probes, revealed a structural change in region 20-29, but not in the reverse region of Trp-19. A guanidine hydrochloride-induced unfolding study showed that the conformational stability of W19Y was greatly reduced by 6.9 kcal/mol compared to that of wild-type beta-LG. These facts indicated that Trp-19 is one of the important residues in correctly maintaining the local structure of beta-LG and stably retaining its overall structure, thereby conserving the bound retinol molecule.

Activation of murine macrophages by polysaccharide fractions from marine algae (Porphyra yezoensis)

Two discrete immunomodulating fractions were obtained from marine algae (Porphyra yezoensis): one was the Porphyra water-soluble fraction (PWSF) which was extracted with hot water from the whole body of algae, and the other was the Porphyra acid-soluble fraction (PASF) which was extracted with acid from the residue. The major constituent in both PWSF and PASF was a polysaccharide, the total sugar concentration in PWSF (56.4%) being lower than that in PASF (82.2%). The high contents of 3,6-anhydrogalactose and sulfate indicated the porphyran structure in PWSF and PASF. The results of an in vitro culture assay with proteose peptone-induced macrophages from mice revealed the PWSF and PASF both enhanced glucose consumption, as well as the production of nitrite and tumor necrosis factor (TNF), but that these were increased more by PWSF than by PASF. PWSF augmented IL-I secretion from these macrophages, while PASF did not. On the other hand, the carbon clearance activity of phagocytes from mice injected intraperitoneally with PASF was higher than that from PWSF-injected mice. The injection of PASF into mice also enhanced the carbon clearance activity in a dose-dependent manner. These results suggest that the two individual fractions possessed the ability to activate macrophages in vitro and in vivo in different ways.

Unfolding/refolding studies on bovine beta-lactoglobulin with monoclonal antibodies as probes. Does a renatured protein completely refold?

We investigated whether any local moieties within a protein molecule could completely refold from the denatured state to regain the native conformation. Bovine beta-lactoglobulin (beta-LG) was denatured in the presence of guanidine hydrochloride (GdnHCl) as the denaturant. Renaturation of the denatured beta-LG was attempted by dialyzing to remove GdnHCl. The renatured molecules regained the same retinol binding activity as that of native beta-LG, and physicochemical studies also indicated that refolding of the denatured beta-LG had been almost completely successful. Local structural differences between the native and renatured beta-LG molecules were evaluated by using our panel of four anti-beta-LG monoclonal antibodies (anti-beta-LG mAbs). The structures of the epitope regions in native beta-LG recognized by two of these mAbs were the same as those in renatured beta-LG. However, it is notable that the binding properties of the other two mAbs to native beta-LG indicated a wide structural difference in the epitope regions between the native and renatured beta-LG. These regions unable to completely refold were the same as those that unfolded preferentially to the alpha-helix region, shown in the previous report (Kaminogawa, S., Shimizu, M., Ametani, A., Hattori, M., Ando, O., Hachimura, S., Nakamura, Y., Totsuka, M., and Yamauchi, K. (1989) Biochim. Biophys. Acta 998, 50-56). Complete refolding was never attained by several renaturation conditions such as quicker or slower removal of the denaturant, nor by additional oxidation treatment after reducing the disulfide bonds. These results suggest that some specific moiety(ies) in a protein molecule cannot return to the native conformation from a denatured state, even if the other moieties refold completely, and that such a conformational difference between renatured and native forms has no affect on the biological function of ligand binding.

Cryptic B cell determinant in a short peptide: T cells do not induce antibody response of B cells when their determinants entirely overlap each other

A synthetic peptide fragment encompassing residues 21-40 (F21-40) of bovine beta-lactoglobulin was used as a model antigen to investigate the relationship between T and B cell determinants. The establishment of fine specificity for these determinants in F21-40 in BALB/c mice revealed that this short peptide contained two T cell determinants, Td1 (residues 21-32) and Td2 (28-40), and that Td2 entirely overlapped the dominant B cell determinant (Bd) of residues 28-40. A truncated peptide, F25-40, was capable of strongly restimulating F21-40-primed T cells in vitro, and its binding affinity to anti-F21-40 antibodies was the same as that of F21-40, indicating that F25-40 maintained the same antigenic structure as that of region 25-40 in F21-40. However, immunization with F25-40 could not elicit specific antibodies despite priming specific T cells. From these results, Bd in F25-40 can be regarded as a cryptic B cell determinant. The absence of antibody response to F25-40 was probably caused by the complete overlapping of Td2 and Bd. This overlapping may have caused the presentation of Td2 only by professional antigen-presenting cells, but never by Bd-specific B cells possessing the potential to be differentiated to antibody-producing cells by T cell help. These findings demonstrate that the co-existence of T and B cell determinants within a single molecule does not always assure specific antibody production, which depends upon the spatial relationship between these determinants.

Dominance and crypticity of T cell antigenic determinants

In this review, we first consider the inherent structural constraints for binding of a peptide to MHC class II molecules. Such parameters at the site of TCR recognition are dependent upon the efficient generation of the antigenic determinant during natural processing of the whole protein antigen. Strikingly, only a minor fraction of such potential determinants on an antigen are presented in an immunodominant manner, while the remaining peptides are silent (cryptic). Why one determinant is selected while the majority are neglected is still unresolved, but we review the experimental evidence pertaining to this choice. Thus, features of the antigen remote from the actual determinant can either steer processing toward disclosure or revelation of a determinant, or interfere with the binding of peptides to MHC (hinderotopy). The evidence is reviewed for "MHC-guided processing," where the unfolding antigen binds at an early stage to an MHC molecule through its most available and affine agretope and then is trimmed down to final size, while the rest of the molecule, including cryptic determinants, is discarded. Different MHC molecules can compete for determinants at an early stage of processing when the antigen is close to its original length. There are shifts in the hierarchy of display of dominant and cryptic determinants, and these shifts relate to local inflammatory states, to changes in the state or composition of the APC population, and to aspects of exogenous vs endogenous processing. The impact of this differential display of determinants on tolerance and autoimmunity is discussed.

Strong influence of the processing of the antigen on negative effects on T cell activation by regions outside the determinant area of bovine alpha s1-casein

alpha s1-Casein can elicit a proliferative response in responding T cell clone 3D20 cells (specific for I-Ab plus fragment 136-151), even when using fixed splenic antigen-presenting cells (APC) not carrying antigen processing ability. The order of potency of each tested antigen for fixed APC was the determinant peptide (136-151) > the long peptide (136-195) > the intact protein (199 residues), indicating that regions outside the determinant area negatively affected the stimulatory potency of the antigens. On the other hand, the order for normal splenic APC was the short peptide > the intact protein > the long peptide. This shows that negative effects by regions outside the determinant area were strongly influenced by the antigen processing.

Differences in defining residues relevant to antibody binding by ELISA and proteolysis protection at the level of peptide antigenic determinants

The interaction of monoclonal antibody (mAb) 1C3 with bovine beta-casein was analyzed by two methods. The competitive enzyme-linked immunosorbent assay in which mAb 1C3 bound competitively to a peptide in solution or beta-casein adsorbed to wells in microtitration plates showed that beta-casein (f194-200) (peptide of residues 194 to 200 of beta-casein) was the shortest peptide among the tested peptides that had binding ability for mAb 1C3. Protection against proteinase digestion was analyzed by incubating proline-specific endopeptidase, carboxypeptidase Y or aminopeptidase T with beta-casein (f193-202) in the presence of mAb 1C3 or nonspecific mAb 31A4. Proteolysis of peptide bonds between residues 200 and 201, and 201 and 202 was depressed in the presence of mAb 1C3. However, peptide bonds between 193 and 194, and 194 and 195 were cleaved in the presence of mAb 1C3 as easily as in the presence of mAb 31A4, suggesting that the region of residues 200 to 202 was obscured by, or within the antibody binding site, but that the region of residues 193 to 195 was not. The apparent antibody binding site shown from the protection against proteolysis by mAb was clearly not identical to the shortest antigen peptide, beta-casein (f194-200), indicated from the competitive binding assay.

T cell determinant structure: cores and determinant envelopes in three mouse major histocompatibility complex haplotypes

T lymphocytes recognize discrete regions on an antigen. The specificity of the T cell responses in three mouse strains of differing major histocompatibility complex (MHC) haplotype to a protein antigen, lysozyme, was analyzed using a series of peptides that walk the antigen in single amino acid steps. These peptide series were synthesized using the pin synthesis system, which was modified to allow the peptides to be cleaved from the pins into a physiological buffer free of toxic compounds. This methodology overcomes many of the problems associated with the production of peptides for screening proteins for antigenic determinants. The T cell determinants for the three strains were markedly different. This result points out the limitations of algorithms predicting determinants without reference to the MHC, and the importance of the empirical methodology. This analysis of the T cell response to lysozyme constitutes the most complete study of reactivity to a foreign protein to date and illustrates many important features of antigen recognition by T cells, e.g., presence of major and minor determinant regions. The outer boundaries of each immunogenic region, the determinant envelope, are difficult to define from recently immunized lymph nodes because of the heterogeneity in T cell recognition. However, core sequences common to all the immunogenic peptides in a continuous sequence can be easily defined.

Monoclonal antibodies as probes for monitoring the denaturation process of bovine beta-lactoglobulin

Five monoclonal antibodies (MAbs) of different idiotypes were produced against bovine beta-lactoglobulin (beta-LG). Among them, MAbs 61B4 and 62A6 reacted preferentially to native beta-LG, while MAbs 21B3 and 31A4 reacted more strongly to the reduced carboxymethylated (denatured) beta-LG than to the native material. These two types of MAb were used to analyze the denaturation process of a beta-LG molecule during heating. The binding affinity of MAbs 21B3 and 31A4 with beta-LG was increased by increasing the heating temperature, the transition temperature being 67-68 degrees C, while that of MAbs 61B4 and 62A6 was reduced by increasing the temperature, this transition temperature being about 80 degrees C. Epitopes recognized by MAbs 31A4 and 61B4 were shown to be included in the segments, Lys8-Trp19 (mostly in the random-coil region) and Thr125-Lys135 (helical region), respectively. The heat-induced conformational change of the beta-LG molecule is, therefore, likely to start in random-coil region as Lys8-Trp19, and to be followed by a structural change in a helical region as Thr125-Lys135. This study demonstrates that MAb is a useful probe to monitor local conformational changes of a protein molecule during denaturation.

Antibody response of three different strains of mice to alpha s1-casein analyzed by using proteolytic and synthetic peptides

The location of immunodominant regions on bovine alpha s1-casein (alpha s1-CN) was compared among three strains of mice (BALB/c, C3H/He and C57BL/6). Anti-alpha s1-CN antisera were separated 5 weeks after the first immunization. Thirty-seven kinds of peptides were obtained from alpha s1-CN by proteolysis, and the segmental 19- to 20-residue peptides overlapping with their adjacent neighbors by 5 residues were synthesized over the entire polypeptide chain of alpha s1-CN. The ability of the anti-alpha s1-CN antibody to bind peptides was tested by an enzyme-linked immunosorbent assay, in which the peptides were adsorbed to the solid phase. All the strains responded highly to alpha s1-CN. The immunodominant antigenic regions of alpha s1-CN were not common to the three strains of mice, the H-2 haplotypes being different from each other (BALB/c, regions 1, 3, 5, 6 and 7; C3H/He, regions 2, 3, 5, 6, 6', 7 and 7'; and C57BL/6, regions 2, 4, 5, 6 and 7).

Rapid screening of antigenically reactive fragments of alpha s1-casein using HPLC and ELISA

Screening of antigenically reactive fragments of alpha S1-casein (alpha S1-CN), the major casein in bovine milk, was done by using HPLC and enzyme-linked immunosorbent assay (ELISA). BALB/c mice (6-week-old) were injected intraperitoneally with alpha S1-CN and complete Freund's adjuvant, and 14 days later, all the mice were boosted with alpha S1-CN and incomplete Freund's adjuvant. Twenty-one days after the 1st immunization, the mice were bled and antiserum was separated. Anti alpha S1-CN antibody fraction was obtained by precipitation from the antiserum with 50% saturated ammonium sulfate. alpha S1-CN was digested with trypsin and chymotrypsin, and 35 peptides were purified from the digests by reversed-phase HPLC with ODS (octadecylsilica) columns. Reactivity of peptides with the antibody were examined by ELISA. The solid phase in the wells of the polystyrene microtiter plate was coated with peptides, and the plate was successively incubated with anti alpha S1-CN antibody, conjugate of anti mouse immunoglobulin with alkaline phosphatase (ALP) and substrate of ALP. Two tryptic fragments (the residues 104-119 and 133-151) and three chymotryptic fragments (33-54, 105-121, and 174-199) were positive in an ELISA test. These five fragments would correspond to four antigenic sites. We could thus find antigenically reactive fragments of alpha S1-CN by the direct and simple detection of specific antigen-antibody interaction.