IgE responses in cats infected with Brugia pahangi

Pathological manifestations in lymphatic filariasis correlate with lack of inhibitory properties of IgG4 antibodies on IgE-activated granulocytes

Helminth parasites are known to be efficient modulators of their host's immune system. To guarantee their own survival, they induce alongside the classical Th2 a strong regulatory response with high levels of anti-inflammatory cytokines and elevated plasma levels of IgG4. This particular antibody was shown in different models to exhibit immunosuppressive properties. How IgG4 affects the etiopathology of lymphatic filariasis (LF) is however not well characterized. Here we investigate the impact of plasma and affinity-purified IgG/IgG4 fractions from endemic normals (EN) and LF infected pathology patients (CP), asymptomatic microfilaraemic (Mf+) and amicrofilaraemic (Mf-) individuals on IgE/IL3 activated granulocytes. The activation and degranulation states were investigated by monitoring the expression of CD63/HLADR and the release of granule contents (neutrophil elastase (NE), eosinophil cationic protein (ECP) and histamine) respectively by flow cytometry and ELISA. We could show that the activation of granulocytes was inhibited in the presence of plasma from EN and Mf+ individuals whereas those of Mf- and CP presented no effect. This inhibitory capacity was impaired upon depletion of IgG in Mf+ individuals but persisted in IgG-depleted plasma from EN, where it strongly correlated with the expression of IgA. In addition, IgA-depleted fractions failed to suppress granulocyte activation. Strikingly, affinity-purified IgG4 antibodies from EN, Mf+ and Mf- individuals bound granulocytes and inhibited activation and the release of ECP, NE and histamine. In contrast, IgG4 from CP could not bind granulocytes and presented no suppressive capacity. Reduction of both the affinity to, and the suppressive properties of anti-inflammatory IgG4 on granulocytes was reached only when FcγRI and II were blocked simultaneously. These data indicate that IgG4 antibodies from Mf+, Mf- and EN, in contrast to those of CP, natively exhibit FcγRI/II-dependent suppressive properties on granulocytes. Our findings suggest that quantitative and qualitative alterations in IgG4 molecules are associated with the different clinical phenotypes in LF endemic regions.

Vaccination of Gerbils with Bm-103 and Bm-RAL-2 Concurrently or as a Fusion Protein Confers Consistent and Improved Protection against Brugia malayi Infection

Background

The Brugia malayi Bm-103 and Bm-RAL-2 proteins are orthologous to Onchocerca volvulus Ov-103 and Ov-RAL-2, and which were selected as the best candidates for the development of an O. volvulus vaccine. The B. malayi gerbil model was used to confirm the efficacy of these Ov vaccine candidates on adult worms and to determine whether their combination is more efficacious.

Methodology and Principle Findings

Vaccine efficacy of recombinant Bm-103 and Bm-RAL-2 administered individually, concurrently or as a fusion protein were tested in gerbils using alum as adjuvant. Vaccination with Bm-103 resulted in worm reductions of 39%, 34% and 22% on 42, 120 and 150 days post infection (dpi), respectively, and vaccination with Bm-RAL-2 resulted in worm reductions of 42%, 22% and 46% on 42, 120 and 150 dpi, respectively. Vaccination with a fusion protein comprised of Bm-103 and Bm-RAL-2 resulted in improved efficacy with significant reduction of worm burden of 51% and 49% at 90 dpi, as did the concurrent vaccination with Bm-103 and Bm-RAL-2, with worm reduction of 61% and 56% at 90 dpi. Vaccination with Bm-103 and Bm-RAL-2 as a fusion protein or concurrently not only induced a significant worm reduction of 61% and 42%, respectively, at 150 dpi, but also significantly reduced the fecundity of female worms as determined by embryograms. Elevated levels of antigen-specific IgG were observed in all vaccinated gerbils. Serum from gerbils vaccinated with Bm-103 and Bm-RAL-2 individually, concurrently or as a fusion protein killed third stage larvae in vitro when combined with peritoneal exudate cells.

Conclusion

Although vaccination with Bm-103 and Bm-RAL-2 individually conferred protection against B. malayi infection in gerbils, a more consistent and enhanced protection was induced by vaccination with Bm-103 and Bm-RAL-2 fusion protein and when they were used concurrently. Further characterization and optimization of these filarial vaccines are warranted.

Onchocerciasis and Lymphatic filariasis (LF) are debilitating neglected tropical diseases (NTDs). Practical challenges in implementation of mass drug administration (MDA) such as prolonged treatment regime requirements and the possible emergence of drug resistance will likely impede the elimination of these NTDs. Hence, the availability of an efficacious prophylactic vaccine would be an invaluable tool. The objective of the present studies was to use the B. malayi-gerbil model of filariasis as a surrogate system to test the efficacy of filarial molecules as vaccine targets for an onchocerciasis vaccine. The vaccine efficacy of Onchocerca volvulus recombinant proteins Ov-RAL-2 and Ov-103 was recently demonstrated using a mouse diffusion chamber model. In this communication, we provide encouraging results on the vaccine efficacy of Bm-RAL-2 and Bm-103, individually or in combination. Our data demonstrate that vaccination with Bm-RAL-2 and Bm-103 concurrently and as a fusion protein confers not only a consistent and significant protection against B. malayi infection in gerbils, but also reduces the fecundity of female worms as demonstrated in embryogram analyses. Our results support the contention that Ov-RAL-2 and Ov-103 are excellent onchocerciasis vaccine candidates and that further investigations leading to their development as a vaccine are warranted.

Immunotherapy with mutated onchocystatin fails to enhance the efficacy of a sub-lethal oxytetracycline regimen against Onchocerca ochengi

Human onchocerciasis (river blindness), caused by the filarial nematode Onchocerca volvulus, has been successfully controlled by a single drug, ivermectin, for over 25 years. Ivermectin prevents the disease symptoms of severe itching and visual impairment by killing the microfilarial stage, but does not eliminate the adult parasites, necessitating repeated annual treatments. Mass drug administration with ivermectin does not always break transmission in forest zones and is contraindicated in individuals heavily co-infected with Loa loa, while reports of reduced drug efficacy in Ghana and Cameroon may signal the development of resistance. An alternative treatment for onchocerciasis involves targeting the essential Wolbachia symbiont with tetracycline or its derivatives, which are adulticidal. However, implementation of antibiotic therapy has not occurred on a wide scale due to the prolonged treatment regimen required (several weeks). In the bovine Onchocerca ochengi system, it has been shown previously that prolonged oxytetracycline therapy increases eosinophil counts in intradermal nodules, which kill the adult worms by degranulating on their surface. Here, in an "immunochemotherapeutic" approach, we sought to enhance the efficacy of a short, sub-lethal antibiotic regimen against O. ochengi by prior immunotherapy targeting onchocystatin, an immunomodulatory protein located in the adult female worm cuticle. A key asparagine residue in onchocystatin was mutated to ablate immunomodulatory activity, which has been demonstrated previously to markedly improve the protective efficacy of this vaccine candidate when used as an immunoprophylactic. The immunochemotherapeutic regimen was compared with sub-lethal oxytetracycline therapy alone; onchocystatin immunotherapy alone; a gold-standard prolonged, intermittent oxytetracycline regimen; and no treatment (negative control) in naturally infected Cameroonian cattle. Readouts were collected over one year and comprised adult worm viability, dermal microfilarial density, anti-onchocystatin IgG in sera, and eosinophil counts in nodules. Only the gold-standard antibiotic regimen achieved significant killing of adult worms, a profound reduction in microfilarial load, and a sustained increase in local tissue eosinophilia. A small but statistically significant elevation in anti-onchocystatin IgG was observed for several weeks after immunisation in the immunotherapy-only group, but the antibody response in the immunochemotherapy group was more variable. At 12 weeks post-treatment, only a transient and non-significant increase in eosinophil counts was apparent in the immunochemotherapy group. We conclude that the addition of onchocystatin immunotherapy to a sub-lethal antibiotic regimen is insufficient to induce adulticidal activity, although with booster immunisations or the targeting of additional filarial immunomodulatory proteins, the efficacy of this strategy could be strengthened.

A comprehensive, model-based review of vaccine and repeat infection trials for filariasis

SUMMARY Filarial worms cause highly morbid diseases such as elephantiasis and river blindness. Since the 1940s, researchers have conducted vaccine trials in 27 different animal models of filariasis. Although no vaccine trial in a permissive model of filariasis has provided sterilizing immunity, great strides have been made toward developing vaccines that could block transmission, decrease pathological sequelae, or decrease susceptibility to infection. In this review, we have organized, to the best of our ability, all published filaria vaccine trials and reviewed them in the context of the animal models used. Additionally, we provide information on the life cycle, disease phenotype, concomitant immunity, and natural immunity during primary and secondary infections for 24 different filaria models.

Future prospects and challenges of vaccines against filariasis

Filarial infections remain a major public health and socio-economic problem across the tropics, despite considerable effort to reduce disease burden or regionally eliminate the infection with mass drug administration programmes. The sustainability of these programmes is now open to question owing to a range of issues, not least of which is emerging evidence for drug resistance. Vaccination, if developed appropriately, remains the most cost-effective means of long-term disease control. The rationale for the feasibility of vaccination against filarial parasites including onchocerciasis (river blindness, Onchocerca volvulus) and lymphatic filariasis (Wuchereria bancrofti or Brugia malayi) is founded on evidence from both humans and animal models for the development of protective immunity. Nonetheless, enormous challenges need to be faced in terms of overcoming parasite-induced suppression without inducing pathology as well as the need to both recognize and tackle evolutionary and ecological obstacles to successful vaccine development. Nonetheless, new technological advances in addition to systems biology approaches offer hope that optimal immune responses can be induced that will prevent infection, disease and/or transmission.

Serum antibody responses to Wolbachia surface protein in patients with human lymphatic filariasis

Wolbachia surface protein (WSP), which is the most abundantly expressed protein of Wolbachia from the human filarial parasite Brugia malayi, was chosen for the present study. B-cell epitope prediction of the WSP protein sequence indicates a high antigenicity, surface probability and hydrophilicity by DNA STAR software analysis. ProPred analysis suggests the presence of HLA class II binding regions in the WSP protein that contribute to T-cell responses and isotype reactivity. In order to validate these findings, the gene coding for endosymbiont WSP was PCR-amplified from the genomic DNA of the human filarial parasite Brugia malayi and cloned in T-7 expression vector pRSET-A. Western blot and ELISA at the total IgG level with recombiant WSP indicated a significantly elevated reactivity in CP compared to MF, EN and NEN individuals. Isotype ELISA also suggested an elevated reactivity in CP patients at the IgG1 level. In contrast, WSP-specific IgG4 levels were found to be elevated in MF patients compared to CP and EN. Besides this, WSP-specific IgE levels indicated an elevated reactivity in CP and MF patients compared to normals. Observations from ELISA supported the in silico predictions that indicate the presence of B- and T-cell epitopes. Hence, a combinatorial approach of in silico predictions and wet-lab studies provides interesting insights into the role of Wolbachia proteins in filarial pathogenesis.

Feline immunoglobulin E: historical perspective, diagnostics and clinical relevance

Immunoglobulin E (IgE) plays a critical role in the immune response to parasitic infections and also mediates pathology in allergic disease. While the role of this antibody in both naturally developing and experimentally induced parasitic and allergic diseases of cats has been recognized for decades, the relatively slow development of reagents specific for feline IgE has hindered studies on clinically important IgE-mediated diseases in the cat. This review highlights the major advances which have been made and discusses the current literature demonstrating the role of IgE in feline parasitic infections and allergy.

T-cell activation and the balance of antibody isotypes in human lymphatic filariasis

Human filarial infection presents a spectrum of clinical states with two major poles: asymptomatic microfilaraemia and amicrofilaraemic chronic disease. Microfilaremia is associated with a Th1-type tolerance, and maximal IgG4 antibodies, while elephantiasis patients react across a broad range of immune parameters. In this review, Rick Maizels and his colleagues discuss recent advances in the immunology of human filariasis and present a summary of their latest studies in an endemic area of Indonesia.

Immunophenotyping of the cutaneous cellular infiltrate after atopy patch testing in cats with atopic dermatitis

Cats with spontaneously occurring atopic dermatitis have clinical and immunocytochemical characteristics compatible with these in humans with atopic dermatitis (AD). The atopy patch test (APT) has proven to be a valuable tool in elucidating the disease process in humans. Additionally, the APT is very specific and bypasses the problem of conflicting results due to differences in chronicity of lesions of AD patients. We adapted the APT for use in cats to explore the suitability of the APT as a tool to study the onset of allergic inflammation in cats with atopic dermatitis. APT were performed in AD cats (n = 6) and healthy cats (n = 10). All cats were patch tested with two allergens in three different dilutions and a diluent control. The allergens for the APT were selected from positive intradermal test and /or prick test results and consisted of: Dermatophagoides farinae, D. pteronyssinus, Tyrophagus putrescentiae, and a grass pollen mixture. APT were read after 10, 24 and 48 h, and punch biopsies for immunohistochemical evaluation were collected at these time points. Macroscopically positive APT reactions were observed in three out of six cats at 24 and/or 48 h with allergen concentrations of 25,000 and 100,000 NU/ml. Reactions were not observed at negative control sites and neither in control animals. A significantly increased number of IL-4+, CD4+, CD3+, MHC class II+ and CD1a+ cells was found in one AD cat with positive APT reactions. Five out of six AD cats had significantly increased IL-4+ T cell numbers at 24 and/or 48 h. Our data indicate that in cats, macroscopically positive patch test reactions can be induced, which have a cellular infiltrate similar to that in lesional skin. We found a high specificity and a macroscopically positive APT reaction in half of the cats, which is similar to what is seen in humans. Hence, the APT in cats might be a useful tool in studying the immunopathogenesis of feline atopic dermatitis.

Parasites and immune responses: memory illusion?

Immunological memory responses to intracellular protozoa and extracellular helminths govern host resistance and susceptibility to reinfection. Humans and livestock living in parasitic disease endemic regions face continuous exposure from a very early age that often leads to asymptomatic chronic infection over their entire lifespan. Fundamental immunological studies suggest that the generation of T-cell memory is driven by tightly coordinated innate and adaptive cellular immune responses rapidly triggered following initial host infection. A key distinguishing feature of immune memory maintenance between the majority of parasitic diseases and most bacterial or viral diseases is long-term antigen persistence. Consequently, functional parasite immune memory is in a continuous, dynamic flux between activation and deactivation producing functional parasite killing or functional memory cell death. In this sense, T-cell immune memory can be regarded as "memory illusion." Furthermore, due to the finite capacity of memory lymphocytes to proliferate, continuous parasite antigen stimulation may exceed a threshold level at some point in the chronically infected host. This may result in suboptimal effector immune memory leading to host susceptibility to reinfection, or immune dysregulation yielding disease reactivation or immune pathology. The goal of this review is to highlight, through numerous examples, what is currently known about T-cell immune memory to parasites and to provide compelling hypotheses on the survival and maintenance of parasite "memory illusion." These novel concepts are discussed in the context of rationale parasite vaccine design strategies.

Evaluation of skin test reactivity to environmental allergens in healthy cats and cats with atopic dermatitis

OBJECTIVE

To evaluate skin test reactivity to environmental allergens in healthy cats and in cats with atopic dermatitis (AD).

ANIMAL

10 healthy cats and 10 cats with AD.

PROCEDURE

10 allergens in serial dilutions were injected ID on the lateral aspect of the thorax of sedated cats. Histamine (0.01% solution) and buffer solutions were used as positive and negative controls, respectively. Immediately after the last injection, 10% fluorescein solution was administered IV. Skin test results were evaluated with ultraviolet light after 15 to 30 minutes and at 4 and 6 hours by 2 independent observers. In the control group, skin tests were repeated after 6 weeks. Skin test reactivity and the nature of the immunoglobulin involved were investigated by use of the Prausnitz-Küstner test with untreated and heat-treated cat sera.

RESULTS

Intertest and interobserver agreement were high when measurement of the diameter of the fluorescent wheal was used to evaluate skin test responses, compared with assessment of its intensity. In both groups of cats, immediate skin test reactivity was observed as an IgE-mediated reaction, as an IgG-mediated reaction, and as a result of nonspecific mast cell degranulation. There was no correlation between allergen concentration and the type of reaction observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Skin test reactivity in cats should be evaluated after IV administration of 10% fluorescein solution by means of a Prausnitz-Küstner test to differentiate among IgE-mediated, IgG-mediated, and nonspecific reactions.

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.

Brugia malayi: establishment in inbred and outbred strains of mice

Immunocompetent mouse model for human filarial parasite Brugia malayi is urgently required in view of the paucity of commercial reagents for other susceptible rodent viz. mastomys and gerbil. Genes within the major histocompatibility complex have been reported to influence the susceptibility of mouse to helminth parasites. Attempts have therefore been made in the present investigation to experimentally infect various inbred strains of mice viz. NZB/BINJ, BALB/c, AKR, C(3)H, and SJL/J with H-2 haplotype (H-2: d, d, k, k, s, respectively) and outbred strains of mice viz. Parks and Swiss. Findings indicate that susceptibility of mice to B. malayi is strain associated. This is the first report on the successful completion of full developmental cycle of subperiodic B. malayi in NZB/BINJ, an immunocompetent mouse strain. In some of the other strains, partial development or low degree of establishment of worms was observed.

Macrophage effector functions controlled by Bruton's tyrosine kinase are more crucial than the cytokine balance of T cell responses for microfilarial clearance

Macrophages from X-linked immunodeficient (xid) mice lacking functional Bruton's tyrosine kinase (Btk) show poor NO induction and enhanced IL-12 induction, and contribute to delayed clearance of injected microfilaria (mf) in vivo. We now show that Btk is involved in other macrophage effector functions, such as bactericidal activity and secretion of proinflammatory cytokines (TNF-alpha, IL-1beta), but not the T cell-directed cytokine IL-12. Induction of some transcriptional regulators of the NF-kappaB family, crucial for the expression of proinflammatory cytokines, is also poor in Btk-deficient macrophages. Thus, Btk appears to be involved in signaling for inducible effector functions, but not APC functions, in macrophages. Furthermore, adoptive transfer of T cells from mf-infected xid or wild-type mice did not alter the course of mf clearance in recipients, mf clearance was unaltered in IFN-gamma-deficient mice, and improved mf clearance was seen only if greater inducibility of IL-12 was accompanied by greater NO secretion from macrophages, as seen in Ity(r) C.D2 mice as compared with congenic Ity(s) BALB/c mice. Thus, delayed mf clearance in xid mice was correlated not with the high IL-12/Th1 phenotype but with low NO induction levels. Also, xid macrophages showed poor toxicity to mf in vitro as compared with wild-type macrophages. Inhibition of NO production blocked this mf cytotoxicity, and an NF-kappaB inhibitor blocked both NO induction and mf cytotoxicity. Thus, Btk is involved in inducing many macrophage effector functions, and delayed mf clearance seen in Btk-deficient xid mice is due to poor NO induction in macrophages, resulting in compromised microfilarial toxicity.

Interleukin 4-producing CD4+ T cells in the skin of cats with allergic dermatitis

Lesional skin of cats with allergic dermatitis has a cellular infiltrate and a CD4/CD8 ratio comparable to that in humans with atopic dermatitis. CD4+ helper T cells and in particular cells belonging to the Th2 subset play an important role in disease pathogenesis in humans. We investigated the cytokine pattern of CD4+ T cells in situ, with special emphasis on the putative presence of cells producing interleukin 4 (IL4), in cats with allergic dermatitis. Immunohistochemical procedures were used to determine that CD4+ T cells in lesional and nonlesional skin of cats with allergic dermatitis can produce IL4, as occurs in humans. Lesional and nonlesional skin of cats with allergic dermatitis had significantly more IL4+ T cells (P = 0.001) than did skin of healthy control cats. Double staining indicated that all IL4+ cells were positive for pan-T or CD4 markers. Double labeling for mast cell chymase and IL4 stained primarily different cells. Western blotting demonstrated cross-reactivity between the antibody against human IL4 and a feline recombinant IL4. These results indicate that IL4 is primarily produced by CD4+ T cells and is also present in clinically uninvolved skin, indicating a role in the pathogenesis of allergic dermatitis in cats.

Immunity to filarial nematodes

Mosquito-borne filarial nematodes cause the severe, debilitating disease of human lymphatic filariasis. In areas endemic for this disease, differential responses range from putative immunity through asymptomatic microfilaraemic infection to chronic pathology. Current research in mouse models of infection is elucidating the immunological mechanisms that can lead to immunity against this disease. In this review, the importance of different immunological pathways are discussed in relation to their role in human disease and in terms of their ability to kill separate developmental stages of the filarial parasite.

Molecular cloning and phylogenetic analysis of a cDNA encoding the cat (Felis domesticus) Ig epsilon constant region

A feline splenic cDNA library was screened with a (32)P-labelled cDNA probe encoding the canine IgE epsilon heavy chain subunit. A cDNA sequence of 1614 nucleotides encoding the complete feline IgE heavy chain, as well as a portion of a variable region, was identified. A search of the GenBank database revealed an identity of 82% at the nucleotide level and 76% at the amino acid level between the feline epsilon heavy chain sequence and the canine homologue. In a separate study, feline genomic DNA, isolated from whole feline embryo cells, was subjected to PCR amplification using primers based on known partial genomic DNA sequences for the feline C epsilon gene. Following removal of an intron from the 683 bp PCR product, the coding sequence yielded an ORF of 506 bp. The DNA sequence of this PCR clone differed by a single nucleotide from the cDNA clone. This difference is silent, and therefore the proteins encoded by the two sequences are identical over the regions cloned and sequenced. Phylogenetic analysis of the constant regions of nine immunoglobulin epsilon genes revealed that the feline cDNA is most similar to the canine homologue.

Partial sequences of feline and caprine immunoglobulin epsilon heavy chain cDNA and comparative binding studies of recombinant IgE fragment-specific antibodies across different species

Parts of the feline and caprine IgE epsilon heavy chain cDNA (third and fourth constant domains, IgEf3/4) were cloned, sequenced, and expressed to raise antibodies (Abs). The DNA and derived protein sequences of the feline recombinant IgEf (rIgEf) shared high homology with the analogous canine parts (81% at the nucleotide and 71% at the protein levels) and the caprine with the ovine ones (95%/84%), respectively. The polyclonal Abs raised in chickens against the feline and caprine rIgEf3/4 were subjected to a comparative binding study utilizing an ELISA including rIgEf and specific Abs to these rIgEf from dog and horse (rIgEf2 and rIgEf3/4) and sheep (rIgEf3/4). All but the ovine-specific rIgEf3/4 Ab were polyclonal, which had been raised in chickens, and bound to most applied rIgEf; the ovine-specific monoclonal mouse Ab recognized only in addition to ovine rIgEf3/4 the closely related caprine rIgEf3/4. Significant, positive correlations were detected between binding reactions of the polyclonal Abs in ELISA and percentage protein sequence homology (p<0.01). Thus, the newly described feline and caprine IgE nucleotide sequences and corresponding Abs represent useful tools for further species-specific and comparative allergy and disease-associated research.

Vaccination against helminth parasites--the ultimate challenge for vaccinologists?

Helminths are multicellular pathogens which infect vast numbers of human and animal hosts, causing widespread chronic disease and morbidity. Vaccination against these parasites requires more than identification of effective target antigens, because without understanding the immunology of the host-parasite relationship, ineffective immune mechanisms may be invoked, and there is a danger of amplifying immunopathogenic responses. The fundamental features of the immune response to helminths are therefore summarised in the context of vaccines to helminth parasites. The contention between type-1 and type-2 responses is a central issue in helminth infections, which bias the immune system strongly to the type-2 pathway. Evidence from both human and experimental animal infections indicates that both lineages contribute to immunity in differing circumstances, and that a balanced response leads to the most favourable outcome. A diversity of immune mechanisms can be brought to bear on various helminth species, ranging from antibody-independent macrophages, antibody-dependent granulocyte killing, and nonlymphoid actions, particularly in the gut. This diversity is highlighted by analysis of rodent infections, particularly in comparisons of cytokine-depleted and gene-targeted animals. This knowledge of protective mechanisms needs to be combined with a careful choice of parasite antigens for vaccines. Many existing candidates have been selected with host antibodies, rather than T-cell responses, and include a preponderance of highly conserved proteins with similarities to mammalian or invertebrate antigens. Advantage has yet to be taken of parasite genome projects, or of directed searches for novel, parasite-specific antigens and targets expressed only by infective stages and not mature forms which may generate immunopathology. With advances under way in parasite genomics and new vaccine delivery systems offering more rapid assessment and development, there are now excellent opportunities for new antihelminth vaccines.

Delayed Clearance of Filarial Infection and Enhanced Th1 Immunity Due to Modulation of Macrophage APC Functions in xid Mice

Bruton’s tyrosine kinase (Btk) mutant CBA/N mice show delayed clearance of injected microfilaria (mf) compared with wild-type CBA/J mice. Anti-mf T cells from CBA/N mice make relatively more IFN-γ than those from CBA/J mice. The anti-mf T cell proliferative responses are also greater in CBA/N mice. This CBA/N immune phenotype is not restricted to filarial Ags, because immunization with pure proteins also yields T cell responses of greater proliferative magnitude skewed away from Th2 cytokines in CBA/N compared with CBA/J mice. The increased magnitude of CBA/N T cell proliferative responses is reflected in increases in both precursor frequencies and clonal burst sizes of responding Ag-specific T cells, and is independent of the source of re-stimulating APCs. Transfer of CBA/J peritoneal resident cells (PRCs) into CBA/N mice before pure protein immunization leads to a wild-type immune phenotype in the recipient CBA/N mice, with a reduction in the proliferative response and a relative decrease in the IFN-γ produced. When wild-type PRC subpopulations are similarly transferred, the wild-type immune phenotype is transferred by macrophages rather than by B cells. Transfer of wild-type PRCs into CBA/N mice before injection of mf also causes similar changes in the anti-mf T cell responses and enhances the clearance of mf. Thus, Btk is involved in critical macrophage APC functions regulating priming of T cells, and can modulate these responses in pathophysiologically relevant fashion in vivo.

Increased numbers of CD4+ and CD8+ T cells in lesional skin of cats with allergic dermatitis

The aim of this study was to characterize T cells in the skin of cats with an allergic dermatitis histologically compatible with atopic dermatitis, since T cells play an important role in the pathogenesis of atopic dermatitis in humans. We observed a significantly greater number of T cells in lesional skin of domestic short-haired cats with allergic dermatitis (n = 10; median age 5.8 years) than in the skin of healthy control animals (n = 10; median age 5.0 years). In the skin of the healthy control animals, one or two CD4+ cells and no CD8+ cells were found. A predominant increase of CD4+ T cells and a CD4+/CD8+ ratio (mean +/- SD: 3.9 +/- 2.0) was found in the lesional skin of 10 cats with allergic dermatitis. The CD4+/CD8+ cell ratio in the skin of healthy control animals could not be determined because of the absence of CD8+ cells. The CD4+/CD8+ cell ratio in the peripheral blood of 10 cats with allergic dermatitis (mean +/- SD: 1.9 +/- 0.4) did not differ significantly from that in 10 healthy control animals (2.2 +/- 0.4). The CD4+/CD8+ cell ratio and predominance of CD4+ T cells in the lesional skin of cats with allergic dermatitis is comparable to that found in atopic dermatitis in humans. In addition, the observed increase of CD4+ T cells in the nonlesional skin of cats with allergic dermatitis compared to the skin of healthy cats is similar to what is seen in humans. Cytokines produced by T cells and antigen-specific T cells are important mediators in the inflammatory cascade resulting in atopic dermatitis in humans. This study is a first step to investigate their role in feline allergic dermatitis.

Production and characterisation of polyclonal antisera against feline IgE

Cats, naturally or experimentally infected with Toxocara cati were immunised with dinitrophenylated ascaris antigen (DNP-Asc). All cats developed immediate skin reactivity to DNP coupled to bovine serum albumin (DNP-BSA) and the sera of the nine cats had a heat labile homocytotropic antibody detectable by homologous Prausnitz-Küstner (PK) tests. Reagin-rich fractions were prepared from these sera and used for the preparation of polyclonal antisera in rabbits. Resultant antisera were passed through a immunoabsorbent column of Sepharose 4B coupled to heated normal cat serum. An immunoabsorbent column prepared with the resultant antisera removed the PK reactivity from the cat sera, and the activity was recovered following acid elution. The antiserum failed to detect any recognised immunoglobulin in cat sera, but precipitated with a heat labile protein with gamma-1 electrophoretic mobility in the sera of parasited cats. These findings support the contention that the antisera are specific for feline IgE.

Modelling variability in lymphatic filariasis: macrofilarial dynamics in the Brugia pahangi--cat model

A striking feature of lymphatic filariasis is the considerable heterogeneity in infection burden observed between hosts, which greatly complicates the analysis of the population dynamics of the disease. Here, we describe the first application of the moment closure equation approach to model the sources and the impact of this heterogeneity for macrofilarial population dynamics. The analysis is based on the closest laboratory equivalent of the life cycle and immunology of infection in humans--cats chronically infected with the filarial nematode Brugia pahangi. Two sets of long-term experiments are analysed: hosts given either single primary infections or given repeat infections. We begin by quantifying changes in the mean and aggregation of adult parasites (inversely measured by the negative binomial parameter, kappa in cohorts of hosts using generalized linear models. We then apply simple stochastic models to interpret observed patterns. The models and empirical data indicate that parasite aggregation tracks the decline in the mean burden with host age in primary infections. Conversely, in repeat infections, aggregation increases as the worm burden declines with experience of infection. The results show that the primary infection variability is consistent with heterogeneities in parasite survival between hosts. By contrast, the models indicate that the reduction in parasite variability with time in repeat infections is most likely due to the 'filtering' effect of a strong, acquired immune response, which gradually acts to remove the initial variability generated by heterogeneities in larval mortality. We discuss this result in terms of the homogenizing effect of host immunity-driven density-dependence on macrofilarial burden in older hosts.

Antibody responses to filarial infective larvae are not dominated by the IgG4 isotype

The humoral immune response in humans to filarial parasites is generally dominated by the IgG4 isotype, when measured by ELISA against somatic adult worm extract. In contrast, as we report here, antibodies reactive to somatic extracts of infective larvae are more equally represented by IgG1 and IgG4. Moreover, binding to surface exposed epitopes in immunofluorescence on larval stages is mediated foremost by IgG1 and IgM, secondarily by IgG2 and IgG3, and very little by IgG4. Both anti-L3 surface and somatic antibodies are strongest in elephantiasis patients, and tend to increase with age. Antibody to the L3 surface is also present in most microfilaraemic individuals who bear no detectable antibodies to the surface of the microfilarial stage. These results demonstrate that a stage- and isotype-specific response is mounted to the L3 surface which should be considered as a possible mediator of concomitant immunity in filariasis.

Cytostatic and cytotoxic effects of activated macrophages and nitric oxide donors on Brugia malayi

The susceptibility of Brugia malayi microfilariae and adults to injury by the murine macrophage cell line J774 activated with gamma interferon and bacterial lipopolysaccharide has been examined in vitro. Parasites of both stages showed a decline in viability over 48 h of coculture with activated macrophages, assessed by their capacity to reduce the tetrazolium salt 3-[4,5-diethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), although adult parasites were more resistant than microfilariae. Removal of parasites to cell-free medium following exposure to activated macrophages for up to 48 h resulted in partial recovery of their capacity to reduce MTT, suggesting that the effects were primarily cytostatic. However, prolonged exposure to activated J774 cells for 72 h resulted in parasite death. Addition of the nitric oxide synthase inhibitor L-NMMA (N(G)-monomethyl-L-arginine monoacetate) indicated that nitric oxide derivatives were responsible for cytostasis and ultimate toxicity. The toxicity of nitric oxide derivatives was confirmed by coincubation of parasites with chemical donors, although far higher concentrations were required than those generated by activated J774 cells, implying additional complexity in macrophage-mediated cytotoxicity. These experiments further suggested that peroxynitrite or its by-products were more potently damaging to filariae than nitric oxide per se. Examination of ultrastructural changes on exposure of parasites to activated macrophages or donors of nitric oxide indicated that hypodermal mitochondria were highly vacuolated, with less prominent cristae. The data are discussed with reference to immunity to lymphatic filariae and their mechanisms of energy generation.

Lymphatic filariasis: What mice can tell us

Human lymphatic filariasis is a major tropical disease in which clinical manifestations range from asymptomatic microfilaraemia to chronic pathology. Investigative immunological research into this disease is hampered by the fact that mice are refractory to the full developmental cycle of this parasitic nematode. However, studies using either single-stage infections or immunocompromised mice have greatly added to our knowledge of the filarial-induced immune pathways leading to protective immunity, pathology and immunological tolerance. In this review, Rachel Lawrence discusses the recent advances in our understanding of the immunology of lymphatic filariasis using the mouse model.

Focal and generalized alopecia

Focal or generalized alopecia is defined as hair loss affecting the ventral, lateral, perineal, and dorsal aspects of the trunk of the cat, usually in a symmetric pattern. This may be attributable to failure of hair coat production, excess loss of hair due to self trauma, or excess shedding of whole hairs. Self trauma is the most common cause of hair loss and is associated particularly with flea allergy dermatitis. Other causes of hair loss are reviewed.

Bancroftian filariasis in Kwale District of Kenya. III. Quantification of the IgE response in selected individuals from an endemic community

One hundred and sixty-two individuals from a community in Kwale District, Kenya, endemic for bancroftian filariasis, were selected for a study on the IgE response to filarial antigen (prepared from adult Brugia pahangi). Following clinical and parasitological examination, the individuals were grouped into different categories, based on the presence/absence of microfilaraemia, the presence/absence of acute or chronic (hydrocele or elephantiasis) clinical manifestations, and age. The total and filarial-specific IgE responses were evaluated in all individuals, and the responses in the various categories were compared with each other and with the responses of control groups of individuals from filariasis-free areas. The majority of individuals from the endemic area had highly elevated serum concentrations of total IgE. Overall and within each clinical category, the concentration of total IgE was higher in those individuals from the endemic area who had microfilaraemias than in those that did not. The majority of individuals from the filariasis endemic area also had significantly elevated levels of filarial-specific IgE. In contrast, the concentration of specific IgE was lower in subjects with microfilariae than in those without, irrespective of their clinical status. Only a small proportion of total IgE was filarial-specific, the mean value varying from 0.4% to 9.8%, depending on category. Among the endemic individuals, the mean proportion of total IgE which was filarial-specific was 3.6 times higher in the microfilaria-negative than in the microfilaria-positive, indicating that much of the filarial-induced IgE in microfilaraemic individuals could be non-specific. No clear relationship was observed between the IgE response and the clinical manifestations or age of the endemic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytophilic antibodies in cats with miliary dermatitis and eosinophilic plaques: passive transfer of immediate-type hypersensitivity

Passive cutaneous anaphylaxis test and Praunitz-Küstner tests were performed in healthy recipient cats with heated and unheated sera of 17 cats suspected of having allergic dermatitis and of 12 healthy control cats. Positive reactions occurred with heated and unheated sera. It was therefore hypothesized that a heat-stabile cytophilic antibody is involved in the pathogenesis of eosinophilic plaques and miliary dermatitis in some cats.

Vaccine research and development for the prevention of filarial nematode infections

The development of vaccines for the prevention of filarial nematode infections is in a state of relative infancy in comparison to vaccines for other parasitic diseases, such as schistosomiasis and malaria. There are many reasons for this slow start. Some of the principal problems are: (1) the lengthy and complex life cycle of these organisms with attendant complex immune responses, (2) the unique characteristics associated with a relatively large number of different pathogens, (3) the lack of suitable model systems for study of medically important infections, (4) the paucity of parasite material for antigen discovery and recombinant library construction, (5) the lack of substantial evidence suggesting the natural occurrence of protective immune responses, and (6) the limited data on mechanisms responsible for protective immunity. As technical hurdles are considered, it is also critical to focus on the characteristics of a vaccine necessary for its eventual utility. In the case of a vaccine for D. immitis a completely successful product will need to approach a 99+% efficacy. This is because of the 99+% efficacy of competitive chemotherapeutic products and the fact that microfilaremia observed on blood examination, resulting from as few as two worms, would present as a vaccine failure. Although very low worm burdens in large dogs could be perceived as success in the context of protection from clinical disease, because of the option of virtually complete chemoprophylactic protection, the typical veterinary practitioner would probably fail to appreciate less than complete vaccine protection. In contrast, a vaccine that produced a reduction in adult worm burdens without complete protection in either lymphatic filariasis or onchocerciasis would be very important. Highly effective chemoprophylactic agents are not widely available for prevention of the human filariases, and dramatically reduced clinical disease provided by less than a completely effective vaccine could occur as the result of fewer adult worms. The importance of developing these vaccines has outweighed the obstacles to this research. There has been a great deal of epidemiological and experimental evidence to suggest a vaccine is feasible and antigen discovery has progressed relatively rapidly within just the past few years. Efforts to generate appropriate larval cDNA libraries are beginning to yield dividends and a variety of fascinating vaccine candidates have been cloned. Additional antigen discovery, research on appropriate modalities for overexpression of genes from these parasites, and the complex tasks associated with vaccinology remain as significant research and development obstacles.(ABSTRACT TRUNCATED AT 400 WORDS)

The complete cDNA and deduced amino acid sequence of equine IgE

The cDNA from a transcript encoding the complete heavy chain of the equine immunoglobulin IgE has been cloned and sequenced. A fragment of the equine epsilon gene was amplified from cDNA using PCR and this fragment was then used to probe a horse cDNA library prepared from peripheral blood lymphocytes. A recombinant clone containing the cDNA encoding the complete horse epsilon chain and its associated V-D-J and leader, was subsequently isolated and sequenced. Comparison of the deduced amino acid sequence of equine IgE with the C epsilon heavy chains of other species indicates it to be most similar to human C epsilon (54%), followed by sheep C epsilon (52%); the greatest sequence similarity was found in the C epsilon 3 and C epsilon 4 domains among the species compared. The associated V-region had greatest similarity in FR1 to those reported for sheep and the cow (> 80%) but less than 60% to the VH sequences of other species in FR3.

Studies on the isolation and characterisation of a reaginic antibody in a cat

A reaginic antibody has been demonstrated, by passive cutaneous anaphylaxis (PCA), in the serum of a cat infected with the microfilariae of Brugia pahangi. Recipient cats and pigs were challenged with an extract of Ascaris suum after either a four-hour or a 72-hour period of sensitisation. When the serum was heat treated at 56 degrees C it lost its PCA activity. Gel filtration of the serum revealed a pattern of positive PCA fractions similar to that observed in other species. Attempts to purify the PCA-positive material by Superose gel filtration and ion exchange chromatography by fast protein liquid chromatography (FPLC) were unsuccessful. Affinity chromatography of PCA-positive material by FPLC on protein A demonstrated two bound peaks, the second of which was PCA-positive and eluted as a single peak by ion exchange chromatography. The PCA-positive material from gel filtration did not bind to protein G. The protein A, PCA-positive peak provides a partially purified reaginic antibody for further study.

Nematodes and the spleen: an immunological relationship

Despite being a major organ of the immune system, the spleen's role in resisting, controlling or simply ameliorating nematode infections has been neglected. A review of both filarial and gastrointestinal nematodes suggests that though it is difficult to fully assess or quantify the organ's importance in vivo, the spleen is prominent in acting against nematode parasites in mammals. One manifestation of this is that transfer of lymphocytes from the spleen of immunised individuals can protect recipients against the disease. Expansion of splenic lymphoid tissue also alludes to its activity during nematode infection. There is a considerable need for investigation of the spleen under natural conditions as well as much more rigorously controlled experiments even in mammals besides birds and other vertebrates.