Differential antibody isotype reactivity to specific antigens in human lymphatic filariasis: gp15/400 preferentially induces immunoglobulin E (IgE), IgG4, and IgG2

Distinct Serum Immunoglobulins Pattern in Egyptian Patients with Chronic HCV Infection Analyzed by Nephelometry

Hepatitis C has emerged as a major worldwide public health problem. The host immune response to HCV infection is composed of both a non-specific immune response, including interferon (IFN) production and natural killer (NK) cell activity, and a virus-specific immune response, including humoral and cellular components. Susceptibility to infection has been related to immunological disturbances. Several studies have provided experimental evidence of disorders of both cellular and humoral immunity. The present study was carried out to evaluate the serum immunoglobulins level (IgG, IgM, IgA) and IgG-subclasses (IgG1-4) in chronic hepatitis C patients in comparison with healthy control patients. This study included 50 patients with biochemical, serologic, virologic, and histologic evidence of chronic hepatitis C. Total IgG, IgA, and IgM were assayed by nephelometry. IgG subclasses were assayed using human IgG subclasses enzyme immunoassay. The results showed a significant increase of total serum IgG and IgM levels found in patients with chronic HCV compared with the healthy control patients (P < 0.001 for each). There was a statistically significant difference in the IgG subclasses (IgG1 to IgG4) between the patients and controls (P < 0.001 for each). On the other hand, no significant difference was found between patients and healthy controls in IgA level (P = 0.4). The normal total serum immunoglobulins pattern is apparently shifted in chronic hepatitis C infection in the Egyptian patients. This pattern may include an ethnic or biologic background and could be used in the differentiation of the patients with minimal liver disease.

Immune responses and disease enhancement during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.

Allergen-specific IgE and IgG4 are markers of resistance and susceptibility in a human intestinal nematode infection

IgG4 has been proposed to act as a 'blocking antibody' due to its ability to compete for the same epitopes as IgE thus preventing IgE-dependent allergic responses. IgG4 and IgE are both elevated in helminth infections and strong anti-parasite IgE responses are associated with resistance to infection. We wished to determine the relationship between anti-parasite IgG4 and IgE and Ascaris lumbricoides infection status. We examined anti-parasite responses, including antibody levels to recombinant Ascaris allergen-1A (rABA-1A), a target of serum IgE in endemic populations. Worm burden was indirectly estimated by measuring parasite egg output in a cross-sectional human population (N = 105). Levels of anti-parasite IgG4 and IgE in patients' plasma were quantified by immunoassay. Global anti-parasite antibody responses did not bear any significant relationships with intensity of Ascaris infection. Individuals who had detectable levels of IgE but not IgG4 to rABA-1A (11%) had lower average levels of infection compared with individuals who produced anti-rABA-1A IgG4 (40%) and sero-negative individuals (49%) (P = 0.008). The ratio of IgG4/IgE in rABA-1A responders positively correlated with intensity of infection (P < 0.025). IgG4 levels positively correlated with infection level in younger children (age 4-11) where average levels of infection were increasing (P = 0.038), whereas allergen specific IgE emerged as a correlate of immunity in older children and adults (age 12-36) where infection levels were decreasing (P = 0.048). Therefore, in a gastrointestinal helminth infection, differential regulation of anti-allergen antibody isotypes relate to infection level. Our results are consistent with the concept that IgG4 antibody can block IgE-mediated immunity and therefore allergic processes in humans.

Immunoglobulin Isotype Profile of Tissue Transglutaminase Autoantibodies is Correlated with the Clinical Presentation of Coeliac Disease

Coeliac disease (CD) is characterized by the appearance of autoantibodies against tissue transglutaminase (tTG-Ab). Immunoglobulin A (IgA) tTG-Ab have been described as excellent diagnostic markers, but the Ig subclass distribution and the importance of isotype tTG-Ab have not yet been established. In this study, using newly developed isotype- and subclass-specific radioligand assays, we examined anti-tTG IgA1, IgA2, IgG1, IgG4 and IgE antibodies in 30 symptomatic, untreated patients with CD and 22 subjects suspected to suffer from silent CD (sCD). Among 30 patients with CD, 27 (90.0%) were positive for IgA1 tTG-Ab, whereas only 12 (40.0%) had autoantibodies of the IgA2 subclass (P <0.001). IgG1, IgG4 and IgE tTG-Ab were detected in 17 (56.6%), 0 and 3 (10.0%) individuals, respectively. IgA1 was also the predominant anti-tTG subclass in patients with sCD (n=20, 90.1%), followed by IgA2 antibodies (n=7, 31.8%), IgG1 antibodies (n=4, 18.2%), IgG4 antibodies (n=1, 4.5%) and IgE antibodies (n=1, 4.5%). The comparison between both groups revealed a significantly higher prevalence of IgG1 antibodies in patients with symptomatic CD (P <0.01). In 10 of 11 subjects undergoing an intestinal biopsy, the diagnosis of an sCD was confirmed. In this subgroup, there was a positive association between the presence of IgA2 and IgG1 tTG-Ab and severe (Marsh 2-3) mucosal abnormalities. In conclusion, patients with symptomatic and sCD predominantly have IgA1 tTG-Ab. IgG1 tTG-Ab are associated with symptomatic disease and, when present in patients with sCD, are correlated with a severe mucosal destruction. These data suggest that tTG-Ab subclasses could reflect inflammatory events associated with epithelial destruction.

Wuchereria bancrofti: cloning and characterization of heat shock protein 70 from the human lymphatic filarial parasite

Heat shock protein 70 (HSP70) was identified as an immunodominant antigen by screening a Wuchereria bancrofti (Wb) microfilarial cDNA library with pooled Wb-infected sera, with 28% of the immunopositive clones coding for Wb-HSP70. The deduced amino acid sequence showed greater than 97 and 85% identity with HSP70 from filarial nematodes and humans, respectively. Recombinant HSP70 (74 kDa) and a recombinant protein from the C-terminal portion (43 kDa) also reacted with pooled Wb-infected sera, suggesting that the C-terminal region of HSP70 contains at least one antibody epitope. Brugia malayi L3 larvae showed increasing levels of HSP70 with increasing temperatures. Further, a polyclonal mouse anti-Wb-HSP70 antibody had reactivity to the HSP70 of cattle filarial parasite Settaria digitata and to human HSP70 derived from a Hep-2 cell line. Immune reactivity to Wb-HSP70 was strong, with uninfected non-endemic normal sera showing significantly greater reactions than sera from filaria-infected individuals. Both immunodominant self-HSP70 and HSP70 from other microbial infections may be primary targets for developing autoantibodies naturally.

Mice genetically deficient in immunoglobulin E are more permissive hosts than wild-type mice to a primary, but not secondary, infection with the filarial nematode Brugia malayi

Primary and secondary murine and human infections with Brugia malayi are characterized by substantial increases in levels of immunoglobulin E (IgE). To investigate whether this is necessary for worm clearance, IgE(-/-) mice were subjected to primary- and secondary-infection protocols. Following a primary infection, IgE(-/-) mice displayed a profound deficit in their ability to clear an intraperitoneal injection of L3 infective-stage larvae in comparison to wild-type counterparts and maintained substantial worm burdens as late as 10 weeks postinfection. Although viable adult parasites were recovered at this late time point from IgE(-/-) mice, the majority of the mice remained free of microfilariae. IgE(-/-) cohorts subjected to a secondary-infection protocol were able to clear the challenge inoculation in an accelerated manner, with kinetics similar to that observed in the wild-type animals. Analysis of the humoral response in IgE(-/-) mice following infection demonstrates a defect in IgG1 and IgG2a production, in addition to the expected lack of IgE. The IgG1 deficiency is no longer evident following a secondary infection. These data imply that deficiencies other than IgE production (i.e., IgG1 production) deficiency may be responsible for the increased permissiveness of IgE(-/-) mice as hosts following infection with B. malayi.

IgG reactive to CTL-directed epitopes of self-antigens is either lacking or unbalanced in atopic dermatitis patients

We previously demonstrated that CTL-directed epitopes derived from non-mutated self-antigens elicit a type-I allergy in the majority of healthy donors (HD) as did the presence of IgE and IgG reactive to these peptides in the sera of the donors. We investigated in this study whether Igs reactive to eight types of CTL-directed peptides were elevated in the sera of 40 patients with atopic dermatitis (AD). Total IgE levels in the sera of AD patients were significantly higher than those of HD, however, no significant differences between the AD patients and the HD were observed in either the serum levels or the positive rates of IgE reactive to seven of the eight peptides. Total IgG levels were not different from each other, however, IgG reactive to the two peptides with no sequence similarity to other species and one peptide that had similarity to DNA helicase II of enterobacteria were not detectable in the sera of the AD patients. Although IgG reactive to the remaining five peptides, which had sequence similarity to other species, were detectable in both the AD patients and the HD, ratios of peptide-specific IgG1/IgG2 were mostly lower in the AD patients than in the HD. These results indicate that IgG reactive to CTL-directed epitopes of self-antigens is either lacking or unbalanced in AD patients. This information may provide new insight into the immune-mechanisms of elevated auto-reactivity of AD patients.

Elevated immunoglobulin E against recombinant Brugia malayi gamma-glutamyl transpeptidase in patients with bancroftian filariasis: association with tropical pulmonary eosinophilia or putative immunity

A major allergen of the lymphatic filarial nematode Brugia malayi, a homologue of gamma-glutamyl transpeptidase (gamma-GT), is involved in the pathology of tropical pulmonary eosinophilia (TPE) through its potent allergenicity and the induction of antibodies against the host pulmonary epithelium. To investigate the immunoglobulin G (IgG) subclass and IgE responses to recombinant B. malayi gamma-GT, we analyzed the results obtained from 51 patients with differing clinical manifestations of bancroftian filariasis. gamma-GT-specific IgG1, rather than IgG4, was the predominant IgG subclass, particularly in patients with TPE (geomean, 6,321 ng/ml; range, 78 to 354,867 ng/ml) and was 75 times higher than in patients with elephantiasis (CP) (P < 0.003) and 185 times higher than in endemic normal individuals (ENL) (P < 0.010). IgG2 responses were low and IgG3 was almost absent, with no significant differences among the groups. gamma-GT-specific IgG4 responses were significantly elevated in those with subclinical microfilaremia (MF) compared to the CP and ENL groups and correlated with the presence of circulating filarial antigen (CAg). More significantly, gamma-GT-specific IgE antibody levels were strikingly elevated in patients with TPE (geomean, 681 ng/ml; range, 61 to 23,841 ng/ml) and in the ENL group (geomean, 106 ng/ml; range, 13 to 1,405 ng/ml) whereas the gamma-GT-specific IgE level was 44 and 61 times lower in those with MF and CP, respectively (P < 0.001). Elevated gamma-GT-specific IgE/IgG4 ratios were demonstrated in patients with TPE (ratio, 45) and ENL (ratio, 107). Because expression of gamma-GT in Brugia infective third-stage larvae (L3) was demonstrated by immunoblot analysis, the elevated gamma-GT-specific IgE antibodies appear to be associated not only with pulmonary pathology but also with possible resistance to infection in lymphatic filariasis.

Lymphatic filariasis-specific immune responses in relation to lymphoedema grade and infection status. I. Cellular responses

The filariasis-specific cellular responsiveness was assessed in 109 adult individuals from a Wuchereria bancrofti-endemic area in north-east Tanzania. There were 9 study groups. Five groups of individuals were negative for microfilariae (mf) and specific circulating filarial antigen (CFA) and had leg lymphoedema of varying severity ranging from early to more advanced grades (pathology groups 1-5). Another group comprised individuals with mixed grades of lymphoedema and positive for mf and/or CFA (mixed pathology group). Three asymptomatic groups consisted of individuals without leg pathology but with different infection status: (i) CFA- and mf-negative individuals, (ii) CFA-positive but mf-negative individuals, and (iii) CFA- and mf-positive individuals. Peripheral blood mononuclear cells were collected and proliferative responsiveness and secretion of interleukin (IL)-4, IL-10 and gamma interferon (IFN gamma) were measured upon stimulation with a Brugia pahangi antigen. No distinct differences in responses were observed between the 5 uninfected pathology groups. Instead, responses were associated with infection status, with generally higher proliferative activity and higher levels of IL-4 and IFN gamma in uninfected as compared to infected individuals. High levels of IL-10 were observed in asymptomatic individuals without infection and in asymptomatic CFA-positive but mf-negative individuals. Asymptomatic individuals with mf had relatively low IL-10 levels. Groups presenting with chronic pathology generally had low levels of IL-10 independently of infection status. The findings thus give no immediate indication that the measured immunological parameters are related to progression of leg pathology. However, alternative interpretations are presented which suggest a possible role of immunological reactions in development of pathology in lymphatic filariasis.

Lymphatic filariasis-specific immune responses in relation to lymphoedema grade and infection status. II. Humoral responses

The filarial-specific humoral responses (IgG1, IgG2, IgG3, IgG4 and IgE) to a Brugia pahangi antigen was assessed in 9 groups of adult individuals from a Wuchereria bancrofti-endemic area in north-east Tanzania. In 5 of the groups, individuals were negative for microfilariae (mf) and circulating filarial antigen (CFA) and had leg lymphoedema of varying severity ranging from early to more advanced grades. A 6th group had mixed grades of lymphoedema and were actively infected with mf and/or CFA. Three groups of asymptomatic individuals with different infection status (mf+CFA+; mf-CFA+; mf-CFA-) were also included. No differences in the antibody levels were observed between the 5 uninfected pathology groups. However, groups with advanced lymphoedema had a significantly higher level of IgG3 as compared to groups with early lymphoedema. A decline in the IgG4/IgE ratios were observed when moving from groups with early to groups with more advanced lymphoedema, which could indicate that increasing levels of IgE relatively to IgG4 are associated with progression of pathology. When all study groups were compared, higher IgG4/IgE ratios were observed in infected groups than in uninfected groups. This could suggest that high levels of IgG4 relative to IgE protect the parasite, whereas the opposite may play a role in parasite killing. When relating IgG4/IgE ratios to levels of gamma interferon (IFN gamma), a clear inverse relationship was observed. Thus, high levels of IFN gamma were found in groups with low IgG4/IgE ratios (uninfected groups) and low levels of IFN gamma were found in groups with high IgG4/IgE ratios (infected groups). The relationship between cellular (IFN gamma) and humoral (IgG4/IgE ratios) responses and their possible role in parasite protection and killing, and in development of early lymphoedema, are discussed.

Cloning and characterisation of mmc-1, a microfilarial-specific gene, from Brugia pahangi

Nine differentially expressed genes were cloned from Brugia pahangi in a screen which sought to identify cDNAs that were differentially expressed between the microfilariae from the mammalian host and the mosquito vector. One gene (mmc-1), that was up-regulated in mammalian-derived microfilariae, was characterised in detail. RT-PCR analysis demonstrated that mmc-1 was specific to the microfilarial stage of the life cycle and was not transcribed by developing microfilariae in utero, but only following the release of the microfilariae from the adult female. Analysis of DNA from other filarial worms suggested that mmc-1 may be a Brugia-specific gene. Using serum samples from individuals exposed to Brugia malayi infection, it was shown that MMC-1 was specifically recognised by antibodies of the IgG3 subclass. mmc-1 has no homologues in the data bases and its function in the parasite is unknown.

Human immunoglobulin isotype profiles produced in response to antigens recognized by monoclonal antibodies specific to Anisakis simplex

BACKGROUND

Anisakis simplex is a medically important pathogen which not only causes anisakiasis but may provoke allergy reactions, ranging from mild urticaria to anaphylactic shock.

OBJECTIVE

To investigate anti-Anisakis isotype profiles in anisakiasis and Anisakis allergy patients.

METHODS

Capture ELISA techniques were used to investigate the isotype profiles of antibodies specific for two defined Anisakis simplex antigens, in serum from Japanese patients with confirmed anisakiasis and from Spanish patients with allergy to Anisakis. The antigens were 'UA2R antigens' (two proteins with MW of 48 and 67 kDa, recognized by our monoclonal antibody UA2) and 'UA3R antigens' (two proteins with MW of 139 and 154 kDa, recognized by our monoclonal antibody UA3).

RESULTS

Considering IgG, the two most frequent isotypes in the response to the UA2R antigens were IgG1 and IgG2, with IgG4 detected in only one case; in response to the UA3R antigens, by contrast, the two most frequent isotypes were IgG1 and IgG4 (though IgG2 remained reasonably frequent). As regards potential utility for serodiagnosis, 95% of the Japanese anisakiasis patients and 84% of the allergy patients showed detectable IgG1 antibodies to the UA3R antigens. Furthermore, all allergy patients showed IgE antibodies to these antigens.

CONCLUSION

Anisakis simplex contains antigens that induce responses which are differentially regulated. Because of their immunogenicity, immunodominance and allergenic nature, we consider that the 139/154-kDa antigens recognized by our MoAb UA3 are good candidates for use in tests for the diagnosis of anisakiasis and of the allergy caused by this parasite.

The effectiveness of different rat IgG subclasses as IgE-blocking antibodies in the rat basophil leukaemia cell model

The degranulation of mast cells in an allergic response is initiated by the aggregation of high-affinity IgE receptors (Fc epsilon RI) by IgE and antigen. Recently it has been shown that such degranulation can be inhibited by cross-linking Fc epsilon RI and low-affinity IgG receptors (Fc gamma RII) which are also expressed by mast cells. The ability of various monoclonal antibodies to block the degranulation of rat basophil leukaemia (RBL) cells sensitized with IgE antidinitrophenyl (DNP) antibodies has been investigated. Sensitized cells were challenged with immune complexes formed using varying concentrations of antigen, and of both high- and low-valency antigen. It is reported here that rat IgG1 antibodies, which are associated in the rat with a Th1-type response, act as highly effective blocking antibodies over a wide concentration range. Rat IgG2a antibodies, which are associated with a Th2-type response, were able only to inhibit degranulation when immune complexes were formed with very low concentrations of high-valency antigen (DNP32-HSA). Under these conditions, some inhibitory activity was seen with high-affinity murine IgA anti-DNP but not with low-affinity rat IgG2b anti-DNP antibody-containing immune complexes. In addition to this inhibitory activity, IgG2a antibodies were shown to be capable of inducing degranulation of cells via unoccupied Fc epsilon RI. These results demonstrate that blocking activity may arise via both inhibitory receptors and by masking of antigen.

Natural immunity to Ascaris lumbricoides associated with immunoglobulin E antibody to ABA-1 allergen and inflammation indicators in children

Children putatively immune to the large roundworm Ascaris lumbricoides were identified in an area of Nigeria where infection is hyperendemic. Immunity was associated with higher levels of serum ferritin, C-reactive protein, and eosinophil cationic protein, indicating ongoing acute phase or inflammatory processes. In contrast, children who were susceptible to the infection had little serological evidence of inflammation despite their high parasite burdens. Immunoglobulin G (IgG) antibody activity in all subclasses was present in high titer in most children but appeared to have no protective function. Despite exceptionally high total IgE levels, there was no evidence that atopic responses to local common allergens was associated with natural immunity to Ascaris. Among those individuals who produced IgG antibody to recombinant ABA-1 allergen of Ascaris, the naturally immune group had significantly more IgE antibody to the allergen than did those susceptible to the infection. IgE antibody responses in conjunction with innate inflammatory processes therefore appear to associate with natural immunity to ascariasis.

Distribution of IgG subclasses in antimonial unresponsive Indian kala-azar patients

Sodium antimony gluconate (SAG) is the mainstay of treatment for visceral leishmaniasis (VL) or kala-azar. In view of the increasing incidence of refractoriness to SAG in India, we compared the levels of parasite-specific IgG and IgG subclasses in 20 longitudinally followed up kala-azar patients. In both SAG-responsive (n = 10) and unresponsive patients (n = 10), the levels of total IgG, IgG1, IgG2, IgG3 and IgG4 were increased, the rank order being IgG1 > IgG2 > IgG3 = IgG4. Following treatment, a significant decrease in total IgG and the four subclasses occurred in the SAG-responsive group, whereas in the SAG-unresponsive group these levels were unchanged or slightly increased. Therefore, monitoring of IgG1 and IgG2 levels in Indian kala-azar patients is a good serologic alternative to monitoring the disease status.

Carrier-dependent suppression of the anti-phosphorylcholine plaque-forming cell response in Trichinella-infected mice is mediated by anti-hapten IgG1 antibodies

In normal mice, the phosphorylcholine(PC)-bearing Trichinella spiralis antigen FCp induces PC-specific IgM antibodies. Infection with T. spiralis appears to suppress this response, without affecting the production of anti-PC antibodies in response to other PC-bearing antigens; the suppression can thus be considered carrier-dependent. Previous work in our laboratory has indicated that the observed suppression is due to a soluble factor present in the serum of infected mice. In the work reported here, we investigated the identity of this factor. After in vitro stimulation with FCp, spleen cells from FCp-primed infected mice showed a stronger anti-PC IgM response than spleen cells from FCp-primed uninfected mice, confirming that cell memory for FCp is unimpaired by infection. Passive transfer of serum from infected mice to normal recipients, followed by immunization of recipients with FCp or another thymus-dependent or thymus-independent PC-bearing antigen, confirmed that the suppressive agent is soluble and that its activity is carrier-dependent. The suppressive agent was retained by immunoaffinity chromatography with PC or rabbit anti-mouse Ig as ligand, showing that it is a PC-specific Ig. Gel filtration of the fractions retained by PC-immunoaffinity, and subsequent identification of Ig isotypes by an ELISA-based procedure, indicated that the suppressive Igs are of the IgG1 isotype. These findings may be relevant for understanding antibody-mediated down-regulation of the immune response.

Setaria digitata adult 14- to 20-kDa antigens induce differential Th1/Th2 cytokine responses in the lymphocytes of endemic normals and asymptomatic microfilariae carriers in bancroftian filariasis

High titers of parasite antigen-specific IgG4 antibodies have been found to be circulating in the peripheral blood of chronic patients, asymptomatic microfilariae carriers, and endemic normals in bancroftian filariasis. But in contrast to this, the titers of antigen-specific IgG1, IgG2, and IgG3 isotype antibodies are much lower. Using soluble antigens of adult Setaria digitata, a cattle parasite which shows strong antigenic reactivity with filaria sera, we have identified, by immunoblot, 14- to 20-kDa antigens which are recognized only by the IgG4 isotype antibodies present in the sera of asymptomatic microfilariae carriers. These 14- to 20-kDa antigens, after fractionation by SDS-PAGE and transfer to nitrocellulose paper, when solubilized and tested in vitro, induced secretion of a higher quantity of IFN-gamma and a lower quantity of IL-4, IL-5, and IL-10 (differential Th1 and Th2 response) in the lymphocytes of endemic normals in comparison to what they induced in the lymphocytes of asymptomatic microfilariae carriers.