Cat allergen-induced cytokine secretion and Fel d 1-immunoglobulin G immune complexes in cord blood

Fetal Phagocytes Take up Allergens to Initiate T-Helper Cell Type 2 Immunity and Facilitate Allergic Airway Responses

RATIONALE

Actively acquired tolerance occurs when foreign antigens come into contact with the immature fetal immune system.

OBJECTIVES

Armed with the knowledge of actively acquired tolerance, we attempted to prenatally abolish or diminish allergic responses.

METHODS

In utero injection of adjuvant-free ovalbumin (OVA) was conducted in Gestational Day 14 FVB/N mouse fetuses. Postnatally, mice were evaluated for their resistance to intraperitoneal OVA sensitization and oral or aerosolized OVA challenge, and then they were examined for humoral and cellular immunological profiles, airway hyperresponsiveness to bronchospastic stimuli, and lung histology. Fluorescent conjugates of OVA were used for further studies of mechanisms.

MEASUREMENTS AND MAIN RESULTS

This presumed tolerogenic action turned out to be a sensitization process with the development of anaphylaxis or heightened recall, T-helper cell type 2-skewed responses to postnatal encounter with OVA. Further postnatal aerosolized OVA stress triggered allergic lungs with functional and structural alterations of airways. The unintended consequence resulted from macrophage-like fetal phagocytes that took up OVA and differentiated toward dendritic cells. These fetal dendritic cell progenitors attenuated proteolysis of endocytosed OVA for delayed presentation in postnatal life. This specialty of fetal phagocytes effectively retains the memory of antigens internalized early before full development of the immune system, leading to an event of in utero sensitization.

CONCLUSIONS

Our results have mechanical implications for prenatal imprinting of atopy and shed light on the importance of fetal phagocytes in shaping the developing immune system and initiating allergic airway diseases.

Maternofetal Transfer of Antibodies and the Influence of Maternal Atopic Status on the Neonate

Background

Epidemiologic evidence has shown that sensitization of allergic diseases develops early in life, even before birth. The gestational environment, including maternal atopic status and transplacentally transferred antibodies to allergens, may be of importance in the sensitization process.

Objective

To investigate maternofetal transfer of antibodies and the influence of maternal atopic status on the neonatal immune response.

Methods

Fifty-seven healthy pregnant women who underwent elective cesarean section (ECS) were recruited. Total and specific IgE (Phadiatop) levels in cord blood (CB) and maternal blood (MB) were determined using the ImmunoCAP assay. MB- and CB-specific IgG1 and IgA1 antibodies against ovalbumin and house dust mite were analyzed by enzyme linked immunosorbent assay. The cytokines, interleukin (IL)-13, interferon (IFN)-γ, and IL-10 in the supernatant of cultured CB mononuclear cells were quantified by enzyme linked immunosorbent assay. Two subgroups were defined based on the maternal levels of specific IgE (atopic group, Phadiatop IgE more than or equal to 0.35 kilo international units of allergen-specific antibody (KUA)/L; nonatopic group, Phadiatop IgE less than 0.35 KUA/L).

Results

Although total IgE was detectable in all MB samples, it could only be detected in 7% (4/57) of the CB samples. Specific IgE was detectable in all MB samples but undetectable in all CB samples. There was no correlation of total IgE between mothers and their neonates. The concentrations of IL-10, IL-13, and allergen-specific IgG1 and IgA1 in the CB samples did not differ significantly between the atopic and nonatopic groups. IFN-γ was undetectable in the CB samples.

Conclusions

Maternal IgE cannot be transferred to the child in utero. Maternal atopic status has no significant effect on neonatal immune responses.

The role of microbes in developmental immunologic programming

The role of microorganisms in the gastrointestinal tract has undergone significant modification in the past few decades with new observations from clinical, epidemiologic, and basic science research. We now know that the perception of these gut microbes as pathogens or even as commensals is somewhat outdated. It is becoming increasingly clear that the gut microbiome plays an important role in a host of activities including digestion, protection from potentially pathogenic organisms, and the regulation and development of the host immune system. The complex interactions between microbes and host combined with recent clinical observations and epidemiologic trends may point to the convergence of two well-supported (though imperfect) hypotheses: the "hygiene hypothesis" and the "fetal programming hypothesis." We are beginning to understand that exposure to microbes before conception, during gestation, and in the neonatal period have profound effects on the developing immune system. Recent observations from a variety of fields help support the expansion of the "fetal programming hypothesis" to a host-microbe corollary that microbe-host interactions at critical windows influence the future immune phenotype, the maintenance of immune health, and the development of immune-mediated disease.

Antibody-dependent transplacental transfer of malaria blood-stage antigen using a human ex vivo placental perfusion model

Prenatal exposure to allergens or antigens released by infections during pregnancy can stimulate an immune response or induce immunoregulatory networks in the fetus affecting susceptibility to infection and disease later in life. How antigen crosses from the maternal to fetal environment is poorly understood. One hypothesis is that transplacental antigen transfer occurs as immune complexes, via receptor-mediated transport across the syncytiotrophoblastic membrane and endothelium of vessels in fetal villi. This hypothesis has never been directly tested. Here we studied Plasmodium falciparum merozoite surface protein 1 (MSP1) that is released upon erythrocyte invasion. We found MSP1 in cord blood from a third of newborns of malaria-infected women and in >90% following treatment with acid dissociation demonstrating MSP1 immune complexes. Using an ex vivo human placental model that dually perfuses a placental cotyledon with independent maternal and fetal circuits, immune-complexed MSP1 transferred from maternal to fetal circulation. MSP1 alone or with non-immune plasma did not transfer; pre-incubation with human plasma containing anti-MSP1 was required. MSP1 bound to IgG was detected in the fetal perfusate. Laser scanning confocal microscopy demonstrated MSP1 in the fetal villous stroma, predominantly in fetal endothelial cells. MSP1 co-localized with IgG in endothelial cells, but not with placental macrophages. Thus we show, for the first time, antibody-dependent transplacental transfer of an antigen in the form of immune complexes. These studies imply frequent exposure of the fetus to certain antigens with implications for management of maternal infections during pregnancy and novel approaches to deliver vaccines or drugs to the fetus.

Maternal-fetal interaction: preconception immunization in mice prevents neonatal sensitization induced by allergen exposure during pregnancy and breastfeeding

Allergen exclusion measures during pregnancy and lactation have been given consideration in studies of primary allergy prevention but complete avoidance of mother/neonatal allergen exposure has proven to be a difficult procedure. To evaluate a strategy to prevent allergen sensitization in early life in mice, we first established a neonatal model with ovalbumin sensitization through maternal allergen exposure during pregnancy or breastfeeding. The modulatory potential of preconception immunization was investigated on the neonatal development of subsequent allergic responses to maternal allergen exposure. Herein, we demonstrate that immunized mothers exposed to antigen during pregnancy or breastfeeding underwent intense vertical transmission of antibodies, including immunoglobulin G (IgG) in complex with ovalbumin and IgG1 antibody with anaphylactic function. It was further shown that maternal immunization efficiently decreased the passage of free antigens through breastfeeding and inhibited the enhanced IgE antibody response after postnatal antigen exposure. In addition, antenatal immunization decreased the antigen-specific proliferative response of immunized neonates, in parallel with profound downmodulatory effects on both the activation and differentiation of T and B cells after a non-specific stimulus and cytokine production. These findings showed that early life sensitization, subsequent to maternal allergen exposure during both the prenatal and postnatal periods, could be avoided by preventive vaccination of the mother.

Prenatal versus postnatal sensitization to environmental allergens in a high-risk birth cohort

BACKGROUND

The timing of allergen sensitization is controversial, with conflicting evidence suggesting transplacental priming versus exclusively postnatal priming. Resolution of this question is important in relation to rational design of allergy prevention strategies, particularly the issue of allergen avoidance during pregnancy.

OBJECTIVE

To elucidate the kinetics of sensitization in high-risk children during their first 2 years of life.

METHODS

We prospectively studied house dust mite (HDM)-specific IgE and IgG(4) antibody production and associated T-cell immunity in a cohort of 200 high-risk infants. Parallel antibody studies tracked responses against a broader panel of inhalant and dietary allergens including peanut.

RESULTS

HDM-induced T(H)2 responses in PBMC from 6 months onward, particularly IL-4 and IL-5, correlated increasingly strongly with sensitization outcomes at 2 years, and a contrasting negative relationship was observed with IFN-gamma response capacity. HDM-induced T-cell responses in cord blood, although common, were unrelated to subsequent sensitization. Transient HDM-IgE (and IgG(4)) production frequently peaked at 6 or 12 months before returning to baseline, which suggests the onset of protective tolerance. This finding contrasted with progressively increasing HDM-IgE titers in children sensitized by 2 years of age. Comparably contrasting patterns were observed in peanut-specific responses in sensitized versus nonsensitized children.

CONCLUSION

Priming of T(H)2 responses associated with persistent HDM-IgE production occurs entirely postnatally, as HDM reactivity in cord blood seems nonspecific and is unrelated to subsequent development of allergen-specific T(H)2 memory or IgE.

CLINICAL IMPLICATIONS

These findings question the scientific basis for existing recommendations for allergen avoidance by high-risk women during pregnancy.