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A study on the immunological basis of the dissociation between type I-hypersensitivity skin reactions to Blomia tropicalis antigens and serum anti-B. tropicalis IgE antibodies

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A study on the immunological basis of the dissociation between type I-hypersensitivity skin reactions to Blomia tropicalis antigens and serum anti-B. tropicalis IgE antibodies
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  RESEARCH ARTICLE Open Access A study on the immunological basis of thedissociation between type I-hypersensitivity skinreactions to  Blomia tropicalis  antigens and serumanti- B. tropicalis  IgE antibodies João CM Ponte 1 , Samuel B Junqueira 1 , Rafael V Veiga 1 , Mauricio L Barreto 2 , Lain C Pontes-de-Carvalho 3 andNeuza M Alcântara-Neves 1* Abstract Background:  Two conditions are used as markers of atopy: the presence of circulating anti-allergen IgE antibodiesand the presence of positive skin prick test (SPT) reactions to allergenic extracts. The correlation between theseconditions is not absolute. This study aimed at investigating immunological parameters that may mediate this lack of correlation. Individuals whose sera contained anti- B. tropicalis  extract IgE antibodies ( a -Bt  E IgE) were divided intotwo groups, according to the presence or absence of skin reactivity to  B. tropicalis  extract ( Bt  E). The followingparameters were investigated: total IgE levels;  a -Bt  E IgE levels; an arbitrary  a -Bt  E IgE/total IgE ratio; the proportionof carbohydrate-reactive  a -Bt  E IgE; the proportion of   a -Bt  E IgE that reacted with  Ascaris lumbricoides  extract (  Al  E);the production of IL-10 by  Bt  E- and  Al  E-stimulated peripheral blood cells (PBMC). Results:  Total IgE levels were similar in the two groups, but  a -Bt  E IgE was significantly higher in the SPT-positivegroup (SPT  + ). A large overlap of   a -Bt  E IgE levels was found in individuals of both groups, indicating that theselevels alone cannot account for the differences in SPT outcome. Individuals of the two groups did not differ,statistically, in the proportion of   a - Bt  E IgE that reacted with carbohydrate and in the production of IL-10 by  Bt  E-and  Al  E-stimulated PBMC. Both groups had part of   a - Bt  E IgE activity absorbed out by  Al  E, indicating the existenceof cross-reactive IgE antibodies. However, the  a - Bt  E IgE from the SPT-negative individuals (SPT-) was moreabsorbed with  AlE   than the  a - Bt  E IgE from the SPT+ individuals. This finding may be ascribed to avidity differencesof the  a - Bt  E IgE that is present in the two groups of individuals, and could occur if at least part of the  a - Bt  E IgEfrom the SPT- individuals were elicited by  A. lumbricoides  infection. Conclusion:  The present results suggest that a low ratio of specific IgE to total IgE levels (in a minority of individuals), and differences in  a - Bt  E IgE avidities (which would have high affinities for  A. lumbricoides  antigens inSPT- than in SPT  +  individuals) may play a role in the down-modulation of type-I hypersensitivity reaction againstaeroallergens described in helminth-infected individuals. Background Asthma is a complex disease whose phenotypic hetero-geneity has been shown to depend both on genetic fac-tors, such as those that underlie the appearance of atopy, and on environmental factors [1,2]. Among theenvironmental factors, one that is  sine qua non  in thedetermination of the development, severity and chroni-city of allergic asthma is the contact with environmen-tal allergens, especially those derived from indoormites, cockroaches, pet epithelia and pollens [3,4].Indeed, atopy is usually defined as an intrinsic condi-tion characterized by the presence of circulating IgEantibodies against those environmental allergens (i.e.,antibodies against innocuous antigens) and/or skinreactivity to the same allergens. Although a good * Correspondence: Neuza@ufba.br 1 Departamento de Biointeração, Instituto de Ciências da Saúde, UniversidadeFederal da Bahia, Av. Reitor Miguel Calmon, Sem no. Canela, Salvador,40110-100, Bahia, BrazilFull list of author information is available at the end of the article Ponte  et al  .  BMC Immunology   2011,  12 :34http://www.biomedcentral.com/1471-2172/12/34 © 2011 Ponte et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative CommonsAttribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction inany medium, provided the srcinal work is properly cited.  association between the presence in the circulation of IgE antibodies and a skin prick test (SPT) positivity forthe same aeroallergen has been reported, especially inhigh-income countries and in affluent sub-populationsof developing countries [5,6], this is not always thecase. Thus, a poor association between these two atopy markers in people from rural communities or non-affluent countries has been observed [7,8]. Recently, inpartial disagreement with previous studies, the ISAACresearch group reported dissociation between theseatopy markers in both affluent and non-affluent popu-lations [9].Helminth infections usually accompany low eco-nomic development in the tropics, and they may play arole in establishing the discrepancy between the pre-sence of positive SPT and allergen-specific IgE antibo-dies (sIgE) found in low-income communities [10].Several hypotheses have been proposed to explain why,in some individuals with sIgE, contact of skin mastcells with allergen does not lead to their degranulation.Some of these hypotheses involve: (i) the competitionof polyclonal IgE raised by helminths with sIgE formast-cell Fc ε  receptors [11]; (ii) anti-allergen IgG4antibodies blocking IgE-mediated immunity and aller-gic processes [12]; (iii) presence of cross-reactive IgEantibodies that react with glycoprotein carbohydratemoieties [ a (1,3)-fucose and ß(1,2)-xylose on N-gly-cans], which are widely present in plants and inverte-brates and produce clinically irrelevant antibodies [13];(iv) the induction of regulatory CD4 + CD25 + Foxp3 + Tcells that are capable of down-regulating the allergicprocess [14].In the present study, six different parameters werestudied in individuals who had circulating IgE antibodiesagainst  B. tropicalis  extract (  Bt  E) and had either a nega-tive (SPT-negative individuals) or positive (SPT-positiveindividuals) result in a SPT in which  Bt  E was used asantigen (  Bt  E SPT). The studied parameters were: (i) thelevels of circulating anti-  B. tropicalis  IgE antibodies( a  Bt  E IgE); (ii) the levels of total circulating IgE; (iii) anarbitrary   a  Bt  E IgE/total IgE ratio; (iv) the proportion of the  a  Bt  E IgE that reacted with carbohydrate antigenicdeterminants; (v) the production of IL-10 by   Bt  E- and  A. lumbricoides  extract (  Al  E)-stimulated blood mono-nuclear cells; (vi) the proportion of   a  Bt  E IgE that cross-reacted with  Al  E.IgE antibodies are usually biologically active inremarkably low concentrations [15]. The identificationof the underlying factors that in some cases may leadthese antibodies to fail to trigger, in the presence of antigen, the most potent of the IgE-associated effectormechanisms, namely the degranulation of mast cells,may be relevant for the development of possible thera-pies for allergic diseases. Results Anti- Bt  E IgE levels and their correlation with wheal sizesof SPT reactions The SPT-positive individuals had higher  a  Bt  E IgE levelsthan the SPT-negative individuals, although a greatoverlap in these antibody levels could be seen betweenthe two groups (p < 0.05; Mann-Whitney U test, Figure1A). A weak, but statistically significant correlation (r =0.385, Pearson ’ s correlation; p < 0.05) was also foundbetween  a -Bt  E IgE levels and the  Bt  E SPT wheal sizes(Figure 1 B). NegativePositive 0.00.40.81.21.62.02.4  A * Result of SPT reaction to B. tropicalis extract    A  n   t   i  -    B .   t  r  o  p   i  c  a   l   i  s    I  g   E  a  n   t   i   b  o   d  y   l  e  v  e   l   (   O   D   4   9   0   ) 0204060801001200.00.51.01.52.02.5 r = 0.385P < 0.05 Wheal size of the SPT reaction to B. tropicalis  extract (mm 2 )    A  n   t   i  -    B .   t  r  o  p   i  c  a   l   i  s    I  g   E  a  n   t   i   b  o   d  y   l  e  v  e   l  s   (   O   D    4   9   0  n  m    ) B      A  n   t   i  -    B .   t  r  o  p   i  c  a   l   i  s    I  g   E   l  e  v  e   l  s   (   O   D    4   9   0  n  m    ) Figure 1  Anti- B. tropicalis  IgE antibody levels (A) andcorrelation between the sizes of the wheals produced by skinprick test (SPT) reaction to  B. tropicalis  extract and anti- B.tropicalis  IgE antibody levels (B) in 32 individuals . Serum anti- B.tropicalis  IgE antibody levels and total IgE were assessed by indirectELISA as described in the Methods section. Each symbol representsthe result obtained from an individual serum. The horizontal solidlines represent the median value of the group results, and thehorizontal dashed line represents the assay cut-off. *, p < 0.05,Mann-Whitney U test and Spearman ’ s correlation. Ponte  et al  .  BMC Immunology   2011,  12 :34http://www.biomedcentral.com/1471-2172/12/34Page 2 of 9  Total IgE and  a  BtE IgE/total IgE ratios No statistical difference in total IgE levels was foundbetween the groups, although a few individuals in theSPT negative group had markedly high IgE levels(Figure 2A). The  a -  Bt  E IgE/total IgE arbitrary ratio wassignificantly smaller in the SPT negative group (p <0.05; Mann-Whitney  ’ s U test), although the ranges of  values between the two groups almost completely over-lapped (Figure 2B). Proportion of   a  Bt  E IgE that reacted with carbohydrateantigenic determinants and IL-10 production byperipheral blood cells Overall, pre-treatment of the  Bt  E-solid phase with meta-periodate/borohydride led to varied degrees of reductionin the binding of IgE, allowing the determination that10 to 60% of the  a  Bt  E IgE present in the sera reactedwith a metaperiodate/borohydride-sensitive antigen(Figure 3). However, no statistically significant differencewas found in the proportion of   a  Bt  E IgE that reactedwith metaperiodate/borohydride-treated  Bt  E betweenthe two studied groups (p > 0.05, Mann-Whitney U test).Blood cells from subjects of the two different groupswere assessed for their capacity to produce IL-10 whencultivated without stimulus or stimulated with  Bt  E,  Al  E,bacillus Calmette-Guérin (BCG) lysate, or pokeweedmitogen (PWM)  in vitro . No statistically significant dif-ferences between the negative SPT and the positive SPTgroups were found (Figure 4). Cross-reactivity of IgE antibodies with  B. tropicalis  and  A.lumbricoides  antigens Sera from SPT-positive and SPT-negative individualswere pre-incubated with increasing amounts of   Al  Ebefore assayed for  a -  Bt  E IgE or total IgE levels. Overall,more reduction in  a -  Bt  E IgE levels was found in thenegative SPT group than in the positive SPT group inall  Al  E concentrations. (Figure 5A). A plateau of reduc-tion was reached when the sera were incubated with 30 μ g/mL of   Al  E: larger concentrations of this extract didnot lead to lower binding of the  a -  Bt  E IgE to the solid-phase  Bt  E (data not shown). However, only with the NegativePositive0.00.40.81.2 Result of SPT reaction to B. tropicalis  extract    T  o   t  a   l   I  g   E   (     g   /  m   L   ) NegativePositive02468 B* Result of SPT reaction to B. tropicalis  extract    A  n   t   i  -    B .   t  r  o  p   i  c  a   l   i  s     I  g   E   /   t  o   t  a   l   I  g   E  r  a   t   i  o Figure 2  Total serum IgE concentrations (A) and anti- B.tropicalis  IgE/total IgE ratio (B )  in individuals with and withoutpositive skin prick test (SPT) results . Serum anti- B. tropicalis  IgEantibody and total IgE levels were assessed by indirect and captureELISA, respectively, as described in the Methods section. Eachsymbol represents the result obtained from an individual serum. Thehorizontal solid lines represent the median value of the groupresults. *, p < 0.05, Mann-Whitney U test. NegativePositive010203040506070 Result of SPT reaction to B. tropicalis  extract    C  a  r   b  o   h  y   d  r  a   t  e  -   b  o  u  n   d  a  n   t   i  -    B .   t  r  o  p   i  c  a   l   i  s    I  g   E  a  n   t   i   b  o   d   i  e  s   (   %   ) Figure 3  Proportion of anti- B. tropicalis  IgE antibodies bindingto carbohydrate epitopes in individuals with and withoutpositive skin prick test (SPT) results . The values represent thereduction in the binding to the  B. tropicalis  extract, in an ELISA, of the antibodies, caused by pre-treating the antigen bymetaperiodate/borohydride, as explained in the Methods section.Each symbol represents the result obtained from an individualserum. The horizontal lines represent the median value of the groupresults. There was no statistically significant difference between thetwo studied groups (p > 0.05, Mann-Whitney U test). Ponte  et al  .  BMC Immunology   2011,  12 :34http://www.biomedcentral.com/1471-2172/12/34Page 3 of 9  lowest concentration of   Al  E (0.3  μ g/mL) that was used,the difference between the groups was statistically signif-icant (p < 0.05, Mann-Whitney U test). In most of thestudied sera, the proportion of total IgE that wasreduced by incubation with  Al  E (Figure 5B) was lowerthan the proportion of   a -Bt  E IgE that was reduced by the same treatment (Figure 5A). In some sera, in fact,the reduction in  a -  Bt  E IgE level was not accompaniedby any measurable reduction in total IgE level. Forinstance, 18 out of 28 sera (64%) had a proportion of their  a -Bt  E IgE inhibited by incubation with 30  μ g/mLof   Al  E (in these 18 sera, the proportion of inhibitedantibody activity ranged from 3 to 79%), whereas only 7of these 28 sera (25%) had their total IgE levels reducedby the same treatment (in these 7 sera, the proportionof reduction in total IgE levels ranged from 2 to 34%). Discussion Some aspects of the immune response that may underliethe absence of a positive  Bt  E SPT in the presence of cir-culating  a -  Bt  E IgE were assessed in a group of poor indi- viduals from a Brazilian northeastern large urban center.Both individuals with positive SPT and individuals withnegative SPT were selected from the same area, and wereprobably subjected to the same social and environmentalconditions, including exposition to the same pathogens.All studied subjects had serum  a -  Bt  E IgE levels clearly above the cut-off of the employed assay.The total IgE levels did not differ in the two studiedgroups, although the levels in three out of the 12 SPT-negative individuals were at least 4.7-fold higher thanthe highest total IgE value in the group of SPT-positiveindividuals. As there was a great overlap of total IgElevels between the two groups, a possible blocking of IgE receptors in mast cells by allergen-unrelated IgEcould not explain the negativity in the SPT in themajority of the individuals. However, since distinct fac-tors may mediate the SPT negativity in differentpatients, one cannot exclude that the high levels of totalIgE in a minority of individuals could be inhibiting, by  -+-+-+-+-+02505007501000  - Bt  E  Al  EPWMBCGResult of SPT reaction to B. tropicalis extract    I   L  -   1   0   (   p   g   /   m   L   ) Figure 4  IL-10 production by peripheral blood cells fromindividuals with positive or negative skin prick test (SPT)reactions to  B. tropicalis  extract ( Bt  E), as indicated in the x-axis .Whole blood cells were assessed for their capacity of producing IL-10  in vitro  either when non-stimulated (-) or when stimulated with Bt  E,  A. lumbricoides  extract (  Al  E), pokeweed mitogen (PWM) orbacillus Calmette-Guérin lysate (BCG), as indicated in the top of thefigure. Columns represent the mean IL-10 concentrations in thesupernatants of cultures from 12 individuals with negative SPT reaction to  Bt  E or from 19 individuals with positive SPT reaction to Bt  E. Vertical bars represent the standard deviations of the means. Nostatistically significant differences were found between the negativeSPT and the positive SPT groups for any of the tested stimulants (p> 0.05, Mann-Whitney U test). 30g.mL -1 3g.mL -1 0.3 g.mL -1 020406080SPT-positive individualsSPT-negative individuals *A  A. lumbricoides extract concentration    R  e   d  u  c   t   i  o  n   i  n   t   h  e   b   i  n   d   i  n  g  o    I  g   E   t  o    B .   t  r  o  p   i  c  a   l   i  s   e  x   t  r  a  c   t   (   %   ) 30g.mL -1 3g.mL -1 0.3 g.mL -1 020406080SPT-positive individualsSPT-negative individuals B  A. lumbricoides extract concentration    R  e   d  u  c   t   i  o  n   i  n   t  o   t  a   l   I  g   E   l  e  v  e   l   (   %   ) Figure 5  Reaction of anti- B. tropicalis  IgE antibodies and totalIgE to  A. lumbricoides  extracts . Sera from individuals with positive(SPT-positive individuals) or negative (SPT-negative individuals) skinprick test reactions to  B. tropicalis  extract were pre-incubated withthe indicated concentrations of   A. lumbricoides  extract and tested inan indirect ELISA using  B. tropicalis  extract as antigen ( A ) or assayedfor total IgE level ( B ). The reductions in anti- B. tropicalis  IgE antibodylevels and total IgE levels were calculated as described in Methodssection. *, p < 0.05, Mann-Whitney U test. Ponte  et al  .  BMC Immunology   2011,  12 :34http://www.biomedcentral.com/1471-2172/12/34Page 4 of 9  competition with low levels of specific IgE, the degranu-lation of mast cells. Indeed, when an arbitrary ratio of specific to total IgE was calculated for each serum, theratios in two out of 12 sera from the SPT-negative indi- viduals were smaller than the smallest ratio observed inthe sera from 20 SPT-positive individuals. In these twoindividuals, therefore, it is possible that the negativity inthe SPT could be due to the blocking of allergen-speci-fic by non-specific IgE. A prediction of this hypothesis isthat the sera from these two individuals would fail tosensitize basophils for  in vitro  allergen-triggered degra-nulation. A larger sample of SPT-positive and SPT-negative individuals than the one used in the presentwork, however, should be studied in order to allow oneto conclude that a significant proportion of SPT-nega-tive individuals have smaller specific to total IgE ratiosthan the SPT-positive individuals.In the studied population,  a -  Bt  E IgE levels were sig-nificantly higher in those subjects presenting with posi-tive SPT than with negative SPT, indicating that highserum specific IgE antibody levels are associated withSPT positivity. In agreement with this finding, a statisti-cally significant correlation, although weak, between cir-culating  a -  Bt  E IgE levels and the mean wheal size of theSPT reactions was observed. However, as a great overlapof   a -  Bt  E IgE levels was found between the SPT-negativeand the SPT-positive groups (11 out of 12 sera from thenegative SPT group, and 11 out of 20 sera from thepositive SPT group, produced ELISA optical densitiesbetween the cut-off and 0.3), the simple explanationthat low levels of specific IgE led to negative SPT in allthe studied individuals does not hold up.Allergenic cross-reactive carbohydrate determinants(CCDs) are sugar moieties of glycoproteins that induceIgE production and cross-react with a broad range of allergens [13]. CCDs have been implicated in the discre-pancy between the presence of specific IgE to pollenand the absence of a positive SPT to that same allergen,as the cross-reactive IgE antibodies seem to be incapableof inducing mast cell degranulation [16]. It is thereforebelieved that the carbohydrate-reactive IgE antibodiesare clinically irrelevant, possibly because they are unableto trigger degranulation by cross-linking the mast-cellreceptors or because they have low affinity for the anti-gen [17]. In the present work, the pre-treatment of   Bt  Ewith metaperiodate/borohydride caused varying reduc-tion levels (from 10 to 60%) in the optical densities thatwere obtained in the ELISA performed with sera fromboth SPT-positive and SPT-negative individuals. How-ever, the difference in percentages of reduction betweenthe positive-SPT and negative-SPT groups was not sta-tistically significant. These carbohydrates-binding IgEantibodies, therefore, do not appear to affect the mastcell-dependent skin response to  B. tropicalis  antigens,unlike the antibodies against pollen antigens [16]. How-ever, the possibility that the IgE antibodies from the twogroups of individuals studied in the present work recog-nize different carbohydrate moieties in the  Bt  E, and theanti-carbohydrate IgE in the SPT-negative individualswould not cross-link mast-cell receptors in the presenceof   B. tropicalis  antigens, cannot be excluded. It would,therefore, be worthwhile to investigate whether carbohy-drate-binding antibodies from the two groups areequally able to sensitize basophils for antigen-triggereddegranulation  in vitro .Helminthic infections have the ability to modulate thehuman immune system and suppress allergic responses,although this does not happen in infections with all hel-minth species [18]. With regard to asthma and atopy,the role of   A. lumbricoides  infections is controversial. Instudies with Chinese and Costa Rican children, anincreased risk of childhood asthma and atopy has beenassociated with  A. lumbricoides  infection [19,20]. How-ever, studies with Cuban and Ethiopian children haveshown that infection with this worm protects againstatopic dermatitis and wheezing [21,22]. In the presentwork, an  A. lumbricoides  extract was used in order tostudy the influence of   Ascaris  antigens in two aspects of the immune response: IL-10 production and presence of cross-reactive antibodies.It has been proposed that a balance between differentpopulations of cytokine-producing lymphocytes, such asTh2 and Th1, and the presence of IL-10 - producingTr1, greatly affect the response to harmless environmen-tal molecules and the development of an allergic inflam-matory response [23]. Moreover, the  in vitro  productionof histamine by human mast cells, derived from umbili-cal cord blood, has been shown to be inhibited by IL-10[24]. In an attempt to assess if there were differences inIL-10 production by peripheral blood cells from indivi-duals with serum  a -  Bt  E IgE, with or without positive  Bt  E SPT, their blood were cultivated in the presence of PWM, BCG lysate,  Bt  E, and  Al  E. The IL-10 productionby the blood cells, subjected to any of the four stimuli,of subjects with and without positive  Bt  E SPT, did notdiffer. This result is consistent with the finding thatmesenteric lymph node cells of IL-10 -/- mice that hadbeen chronically infected with the helminth  Heligmoso-moides polygyrus , when transferred into uninfected aller-gen-sensitized wild-type recipients, suppressed theallergic inflammation, leading to the conclusion that thecells activated by   H. polygyrus  infection do not dependon intrinsic IL-10 to suppress the allergic response [14].This is a controversial issue and probably depends onthe species of helminth and/or of the host. For instance,Gabonese children with urinary schistosomiasis havebeen shown to have a lower prevalence of a positiveskin reaction to house-dust mite than those without the Ponte  et al  .  BMC Immunology   2011,  12 :34http://www.biomedcentral.com/1471-2172/12/34Page 5 of 9
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