Cyro Alves de Brito

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.

Maternal immunization with ovalbumin prevents neonatal allergy development and up-regulates inhibitory receptor FcγRIIB expression on B cells

BackgroundPreconception allergen immunization prevents neonatal allergen sensitization in mice by a complex interaction between regulatory cells/factors and antibodies. The present study assessed the influence of maternal immunization with ovalbumin (OVA) on the immune response of 3 day-old and 3 week-old offspring immunized or non-immunized with OVA and evaluated the effect of IgG treatment during fetal development or neonatal period.ResultsMaternal immunization with OVA showed increased levels of FcγRIIb expression in splenic B cells of neonates, which were maintained for up to 3 weeks and not affected by additional postnatal OVA immunization. Maternal immunization also exerted a down-modulatory effect on both IL-4 and IFN-γ-secreting T cells and IL-4 and IL-12- secreting B cells. Furthermore, immunized neonates from immunized mothers showed a marked inhibition of antigen-specifc IgE Ab production and lowered Th2/Th1 cytokine levels, whereas displaying enhanced FcγRIIb expression on B cells. These offspring also showed reduced antigen-specific proliferative response and lowered B cell responsiveness. Moreover, in vitro evaluation revealed an impairment of B cell activation upon engagement of B cell antigen receptor by IgG from OVA-immunized mice. Finally, in vivo IgG transference during pregnancy or breastfeeding revealed that maternal Ab transference was able to increase regulatory cytokines, such as IL-10, in the prenatal stage; yet only the postnatal treatment prevented neonatal sensitization. None of the IgG treatments induced immunological changes in the offspring, as it was observed for those from OVA-immunized mothers.ConclusionMaternal immunization upregulates the inhibitory FcγRIIb expression on offspring B cells, avoiding skewed Th2 response and development of allergy. These findings contribute to the advancement of prophylactic strategies to prevent allergic diseases in early life.

Balance between early life tolerance and sensitization in allergy: dependence on the timing and intensity of prenatal and postnatal allergen exposure of the mother

Allergens can be maternally transferred to the fetus or neonate, though it is uncertain how this initial allergen exposure may impact the development of allergy responses. To evaluate the roles of timing and level of maternal allergen exposure in the early life sensitization of progeny, female BALB/c mice were given ovalbumin (OVA) orally during pregnancy, lactation or weekly at each stage to investigate the immunoglobulin E (IgE) antibody production and cellular responsiveness of their offspring. Exposure to OVA during pregnancy was also evaluated in OVA‐specific T‐cell receptor (TCR) transgenic (DO11.10) mice. The effect of prenatal antigen exposure on offspring sensitization was dependent on antigen intake, with low‐dose OVA inducing tolerance followed by neonatal immunization that was sustained even when pups were immunized when 3 weeks old. These offspring received high levels of transforming growth factor‐β via breastfeeding. High‐dose exposure during the first week of pregnancy or perinatal period induced transient inhibition of IgE production following neonatal immunization; although for later immunization IgE production was enhanced in these offspring. Postnatal maternal antigen exposure provided OVA transference via breastfeeding, which consequently induced increased offspring susceptibility to IgE antibody production according to week post‐birth. The effect of low‐dose maternal exposure during pregnancy was further evaluated using OVA transgenic TCR dams as a model. These progeny presented pronounced entry of CD4+ T cells into the S phase of the cell cycle with a skewed T helper type 2 response early in life, revealing the occurrence of allergen priming in utero. The balance between tolerance and sensitization depended on the amount and timing of maternal allergen intake during pregnancy.

The neonatal immune system: immunomodulation of infections in early life

The innate and adaptive immune responses in neonates are usually functionally impaired when compared with their adult counterparts. The qualitative and quantitative differences in the neonatal immune response put them at risk for the development of bacterial and viral infections, resulting in increased mortality. Newborns often exhibit decreased production of Th1-polarizing cytokines and are biased toward Th2-type responses. Studies aimed at understanding the plasticity of the immune response in the neonatal and early infant periods or that seek to improve neonatal innate immune function with adjuvants or special formulations are crucial for preventing the infectious disease burden in this susceptible group. Considerable studies focused on identifying potential immunomodulatory therapies have been performed in murine models. This article highlights the strategies used in the emerging field of immunomodulation in bacterial and viral pathogens, focusing on preclinical studies carried out in animal models with particular emphasis on neonatal-specific immune deficits.

Role of nitric oxide in immune responses against viruses: beyond microbicidal activity

IntroductionNitric oxide (NO) is a free radical produced during l-arginine metabolism. In addition to its physiological activities in vascular and neuronal functions, its role in the immune system as a microbicide and tumor-killing mediator has been well described, as well as its release by activated macrophages. Furthermore, NO is produced by a variety of immune and non-immune cells and is involved in the regulation of several immune functions, such as T-cell polarization and suppression.ResultsViral infections generally promote NO production; however, according to its concentration, NO can trigger different effector mechanisms in immune responses. NO can activate the second messenger cyclic guanosine monophosphate (cGMP), can increase the cytoplasmic p53 tumor suppressor molecule, and can modify host and viral molecules by nitrosylation. Because of its microbicide function, NO has frequently been considered a protective mediator in viral infections; however, in some cases NO could be deleterious, potentiating inflammation or contributing to virus latency.ConclusionsThus, advances in the knowledge of the role of NO in immunomodulation and in the pathogenesis of viral diseases could contribute not only to the development of vaccines and therapeutic strategies but also to the use of its metabolites (nitrate/nitrite) and the enzyme responsible for its production (iNOS) as prognostic markers of some of these viral infections.

Immune adjuvants in early life: targeting the innate immune system to overcome impaired adaptive response

The neonatal phase is a transitory period characterized by an absence of memory cells, favoring a slow adaptive response prone to tolerance effects and the development of Th2-type responses. However, when appropriately stimulated, neonates may achieve an immune response comparable with adult counterparts. One strategy to stimulate the immunological response of neonates or children in early infancy has been to explore natural or synthetic ligands of cell receptors to stimulate innate immunity. The use of adjuvants for activating different cell receptors may be the key to enhancing neonatal adaptive immunity. This review highlights recent advances in the emerging field of molecular adjuvants of innate immune response and their implications for the development of immunotherapies, with particular focus on the neonatal period.

Bystander effect in synergy to anergy in oral tolerance of Blomia tropicalis/ovalbumin murine co-immunization model.

Oral tolerance is an important approach in allergic diseases and murine model can provide useful information to improve its understanding and therapeutic measures. To address the influence of non-related allergen sensitization in immunized mice with the mite Blomia tropicalis (Bt) or ovalbumin (OVA) or with both Bt/OVA allergens. Furthermore, we sought to verify oral tolerance effect in the Bt/OVA co-immunization model. Mice sensitized with Bt and then exposed to OVA developed an enhanced IgE response to both allergens; contrariwise, this effect was not observed when OVA-sensitization was prior to Bt-sensitization. Co-injection of Bt and OVA led to a dominant IgE response towards OVA over Bt, which was not observed when co-immunization was performed with a 240-fold less amount of OVA. Induction of oral tolerance with OVA, prior to co-immunization, suppressed IgE response to both allergens, probably as a consequence of the increased levels of IFN-γ found in these animals. The results evidenced that, depending on allergenic potential, new allergen exposure may exert an adjuvant effect to the first allergen used in the sensitization. The bystander suppression to non-related allergens through oral tolerance should be a useful mechanism to control sensitization to new allergens.

Mucosal and systemic anti-GAG immunity induced by neonatal immunization with HIV LAMP/gag DNA vaccine in mice

Vaccines capable of inducing mucosal immunity in early postnatal life until adulthood, protecting early sexual initiation, should be considered as strategies to vaccination against HIV. The HIV-1 GAG protein as a chimera with the lysosome-associated membrane protein (LAMP/gag), encoded by a DNA vaccine, is targeted to the endosomal/lysosomal compartment that contains class II MHC molecules and has been shown to be immunogenic in adult mice. Assuming that one such strategy could help to overcome the immunological immaturity in the early postnatal period, we have evaluated the systemic and mucosal immunogenicity of LAMP/gag immunization in neonatal mice. Intranasal immunization with LAMP/gag vaccine induced higher levels of sIgA and IgG anti-GAG antibodies in intestinal washes than did the gag vaccine. The combination of ID injections and the IN protocol with the chimeric vaccine promoted the increase of Ab levels in sera. Both vaccines induced splenic IFN-γ- secreting cells against GAG peptide pools, as well as in vivo cytotoxic T lymphocyte (CTL) function, and increased the percentage of CD8+ T cells to the immunodominant class I peptide in gut and spleen. However, only the chimeric vaccine was able to enhance Th1/Th2 cytokine secretion in response to class II GAG peptide and to enhance IL-4-secreting cells against GAG peptides and p24 protein stimuli. Long-lasting humoral and cellular responses were detected until adult age, following neonatal immunization with the chimeric vaccine. The LAMP/gag vaccination was able to induce potent GAG-specific T and B cell immune responses in early life which are essential to elicit sustained and long-lasting mucosal and systemic humoral response.

Immunization of neonatal mice with LAMP/p55 HIV gag DNA elicits robust immune responses that last to adulthood.

Successful T cell priming in early postnatal life that can generate effective long-lasting responses until adulthood is critical in HIV vaccination strategies because it prevents early sexual initiation and breastfeeding transmission of HIV. A chimeric DNA vaccine encoding p55 HIV gag associated with lysosome-associated membrane protein 1 (LAMP-1; which drives the antigen to the MIIC compartment), has been used to enhance cellular and humoral antigen-specific responses in adult mice and macaques. Herein, we investigated LAMP-1/gag vaccine immunogenicity in the neonatal period in mice and its ability to generate long-lasting effects. Neonatal vaccination with chimeric LAMP/gag generated stronger Gag-specific immune responses, as measured by the breadth of the Gag peptide-specific IFN-gamma, proliferative responsiveness, cytokine production and antibody production, all of which revealed activation of CD4+ T cells as well as the generation of a more robust CTL response compared to gag vaccine alone. To induce long-lived T and B cell memory responses, it was necessary to immunize neonates with the chimeric LAMP/gag DNA vaccine. The LAMP/gag DNA vaccine strategy could be particularly useful for generating an anti-HIV immune response in the early postnatal period capable of inducing long-term immunological memory.

Staphylococcal enterotoxin B induces specific IgG4 and IgE antibody serum levels in atopic dermatitis

Atopic dermatitis (AD) is a chronic recurrent inflammatory disease, with prevalence of about 10–20% in children and 1–3% in adults. Staphylococcus aureus is present in 80–100% of skin from atopic patients and is related to worsening of the disease by the action of enterotoxins. The aim of this study was to evaluate the profile of anti‐Staphylococcus aureus enterotoxin B (SEB) antibody isotypes and IgG subclass levels in adult AD.