Altered T lymphocyte phenotype at birth in babies born to atopic parents

The relationships among immunoglobulin levels, allergic sensitization, and viral respiratory illnesses in early childhood

IgE plays an essential role in type I allergy, however, there is less information about the relationship between other immunoglobulins (IgA and IgG) and atopic phenotypes in early childhood. We hypothesized that levels of circulating IgA in early childhood would be inversely related to the number of respiratory infections and the risk of becoming sensitized to allergens. Immunoglobulin levels were analyzed (ELISA) in plasma samples (IgG, IgA), and in nasal secretions (IgA) from children participating in a high-risk birth cohort study. Samples were available from 264 children at age 2 yr and 257 children at age 4 yr, and results were compared to rates of respiratory illnesses, allergic sensitization, atopic dermatitis (AD), and asthma. Children who were sensitized to allergens had higher rather than lower levels of circulating IgA. A subgroup analysis showed that IgA levels were increased in relationship to foods sensitization (58 vs. 50 mg/dl, p = 0.003) but not aeroallergen sensitization (52 vs. 53 mg/dl, p = 0.11). IgA levels in the plasma correlated with levels of IgE levels (r(s) =0.19, p = 0.003). Levels of IgE, but not IgG or IgA, were positively correlated with rates of respiratory illnesses, AD, and the risk of developing asthma. Finally, there were no significant relationships between IgA in nasal secretions and infectious outcomes. In conclusion, low-normal concentrations of plasma IgA are associated with a reduced prevalence of allergic sensitization in infancy. Further, levels of IgA and IgG in plasma within the range of normal, and IgA in nasal secretions, do not appear to influence the risk of subsequent respiratory illnesses. Further studies to define relationships between IgA and allergic sensitization are likely to provide new insights into the pathogenesis of allergic diseases in infancy.

The Urban Environment and Childhood Asthma (URECA) birth cohort study: design, methods, and study population

BACKGROUND

The incidence and morbidity of wheezing illnesses and childhood asthma is especially high in poor urban areas. This paper describes the study design, methods, and population of the Urban Environment and Childhood Asthma (URECA) study, which was established to investigate the immunologic causes of asthma among inner-city children.

METHODS AND RESULTS

URECA is an observational prospective study that enrolled pregnant women in central urban areas of Baltimore, Boston, New York City, and St. Louis and is following their offspring from birth through age 7 years. The birth cohort consists of 560 inner-city children who have at least one parent with an allergic disease or asthma, and all families live in areas in which at least 20% of the population has incomes below the poverty line. In addition, 49 inner-city children with no parental history of allergies or asthma were enrolled. The primary hypothesis is that specific urban exposures in early life promote a unique pattern of immune development (impaired antiviral and increased Th2 responses) that increases the risk of recurrent wheezing and allergic sensitization in early childhood, and of asthma by age 7 years. To track immune development, cytokine responses of blood mononuclear cells stimulated ex vivo are measured at birth and then annually. Environmental assessments include allergen and endotoxin levels in house dust, pre- and postnatal maternal stress, and indoor air nicotine and nitrogen dioxide. Nasal mucous samples are collected from the children during respiratory illnesses and analyzed for respiratory viruses. The complex interactions between environmental exposures and immune development will be assessed with respect to recurrent wheeze at age 3 years and asthma at age 7 years.

CONCLUSION

The overall goal of the URECA study is to develop a better understanding of how specific urban exposures affect immune development to promote wheezing illnesses and asthma.

Prevalence of asthma among Chinese adolescents living in Canada and in China

BACKGROUND

Studies of the prevalence of asthma among migrating populations may help in identifying environmental risk factors.

METHODS

We analyzed data from Vancouver, Canada, and from Guangzhou, Beijing and Hong Kong, China, collected during phase 3 of the International Study of Asthma and Allergies in Childhood. We subdivided the Vancouver adolescents according to whether they were Chinese immigrants to Canada, Canadian-born Chinese or Canadian-born non-Chinese. We compared the prevalence of asthma and wheezing among Chinese adolescents born in Canada, Chinese adolescents who had immigrated to Canada and Chinese adolescents living in China.

RESULTS

Of 7794 Chinese adolescents who met the inclusion criteria, 3058 were from Guangzhou, 2824 were from Beijing, and 1912 were from Hong Kong. Of 2235 adolescents in Vancouver, Canada, 475 were Chinese immigrants, 617 were Canadian-born Chinese, and 1143 were Canadian-born non-Chinese. The prevalence of current wheezing among boys ranged from 5.9% in Guangzhou to 11.2% in Canadian-born Chinese adolescents. For girls, the range was 4.3% in Guangzhou to 9.8% in Canadian-born Chinese adolescents. The prevalence of ever having had asthma ranged from 6.6% to 16.6% for boys and from 2.9% to 15.0% for girls. Prevalence gradients persisted after adjustment for other environmental variables (odds ratios for ever having had asthma among Canadian-born Chinese compared with native Chinese in Guangzhou: 2.72 [95% confidence interval 1.75-4.23] for boys and 5.50 [95% confidence interval 3.21-9.44] for girls; p < 0.001 for both). Among Chinese adolescents living in Vancouver, the prevalence of ever wheezing increased with duration of residence, from 14.5% among those living in Canada for less than 7 years to 20.9% among those living their entire life in Canada. The same pattern was observed for the prevalence of ever having had asthma, from 7.7% to 15.9%.

INTERPRETATION

Asthma symptoms in Chinese adolescents were lowest among residents of mainland China, were greater for those in Hong Kong and those who had immigrated to Canada, and were highest among those born in Canada. These findings suggest that environmental factors and duration of exposure influence asthma prevalence.

Novel human in vitro system for evaluating antimycobacterial vaccines

Major research efforts are directed towards the development of a better antimycobacterial vaccine. But progress in the field of tuberculosis vaccine development has been hampered by the lack of human in vitro models to assess vaccine immunogenicity and efficacy. New candidate vaccines will have to be evaluated against the existing Mycobacterium bovis BCG "gold standard." It is therefore important to understand the type of immune responses elicited by BCG vaccination to enable comparisons with potential new candidates. We used a novel human in vitro whole-blood model, which measures immune responses to mycobacteria by use of reporter gene-tagged BCG (BCG lux), to study immune responses to BCG vaccination in 50 neonates in a setting in Cape Town, Republic of South Africa, where tuberculosis is endemic. BCG vaccination significantly reduced growth of BCG lux in whole blood (prevaccination median growth ratio [GR], 9.6; range, 1.3 to 24; postvaccination median GR, 3.9; range, 0.6 to 12.2 [P < 0.0001]). Growth of BCG lux was better restricted in vaccinated infants than in unvaccinated age-matched controls (n = 4). BCG vaccination induced significantly higher gamma interferon production in response to BCG lux (P < 0.0001) and to purified protein derivative (P = 0.0001). No significant changes in either growth of BCG lux or cytokine production occurred in an adult control group (n = 6) over the study period. The whole-blood luminescence model detects changes in cellular immune responses to mycobacteria induced by BCG vaccination. It is therefore a useful new tool in studying the immunogenicity of newly developed vaccine candidates prior to large field trials assessing efficacy.

Human milk--derived oligosaccharides and plant-derived oligosaccharides stimulate cytokine production of cord blood T-cells in vitro

Human milk contains large amounts of free oligosaccharides (HMOs). HMOs have been shown to exert antiinflammatory properties, and evidence for their immunomodulatory effects is increasing. The purpose of this study was to evaluate influences of two human breast milk-derived oligosaccharide samples (neutral and acidic oligosaccharides), and of a low-molecular-weight fucoidan on cytokine production and activation of cord blood mononuclear cells. Cord blood mononuclear cells from randomly chosen healthy newborns were co-cultured with the oligosaccharide samples. By means of flow cytometry, intracellular cytokine production (d 20) and surface marker expression of T cells (d 5) were measured. In vitro-induced Ig levels were quantified nephelometrically (total IgG1) and by ELISA (total IgE) in the supernatant of cell cultures. The acidic oligosaccharide fraction increased the percentage of interferon-gamma producing CD3+CD4+ and CD3+CD8+ cells (p < 0.05) and the IL-13 production in CD3+CD8+ cells (p < 0.05). In acidic oligosaccharide cultures, CD25+ expression on CD3+CD4+ cells was significantly elevated (p < 0.05). Low-molecular-weight fucoidan induced IL-4 production in CD3+CD4+ T cells (p < 0.05) and IL-13 production in CD3+CD8+ T cells (p < 0.05), whereas interferon-gamma production remained unaffected in both T-cell populations. Ig production (total IgE and total IgG1) remained unaffected. Human milk-derived oligosaccharides and plant-derived oligosaccharides affect the cytokine production and activation of cord blood derived T cells in vitro. Therefore, oligosaccharides and, in particular, acidic oligosaccharides may influence lymphocyte maturation in breast-fed newborns.

Maternally delivered nutritive allergens in cord blood and in placental tissue of term and preterm neonates

BACKGROUND

The proliferation of cord blood mononuclear cells in response to nutritive and inhalant allergens implies intrauterine exposure with resulting T cell priming. However, the mechanisms triggering these fetal allergen-specific immune responses are incompletely understood.

METHODS

We studied the placental release of endogenous beta-lactoglobulin (BLG) and ovalbumin (OVA) by the use of an open ex vivo placental perfusion model. Preterm and term placentas were obtained immediately after delivery to recover functionally active fetal and maternal circulations. Fetal and maternal perfusate samples were collected throughout the perfusion experiments with medium. Matched cord blood samples were collected separately. All samples were tested for the presence of OVA and BLG by allergen-specific ELISAs.

RESULTS

In 16 out of 19 placentas, the nutritive allergens could be detected both in fetal and maternal perfusate samples. Fetal wash out levels of the allergens BLG and OVA from the placental tissue of preterm and term deliveries were observed in traces and up to 44.4 and 2.6 ng/mL, respectively. In cord blood of preterm and term neonates, BLG and OVA could be detected at concentrations up to 16.7 and 5 ng/mL, respectively.

CONCLUSION

These findings provide direct evidence for the release of tiny amounts of nutritive allergens from placental tissue indicating diaplacental allergen transfer and fetal exposure to nutritive allergens in vivo.

Immune and airway effects of house dust mite aeroallergen exposures during postnatal development of the infant rhesus monkey

BACKGROUND

The effect of chronic environmental aeroallergen exposure on the immune system and airways has not been experimentally defined in very young children.

OBJECTIVE

The purpose of this study was to determine the immunophenotype of peripheral blood and airway leucocytes in the newborn rhesus macaque monkey, following recurrent aerosol exposure to house dust mite (HDM) (Dermatophagoides farinae).

METHODS

A regimen of HDM aerosolization was initiated for 2 h per day, three times per week, starting when rhesus macaque monkeys were 1 week of age. All monkeys were inoculated with diptheria, tetanus, and acellular pertussis vaccine at 5 weeks of age to simulate human infant vaccination schedules.

RESULTS

Following 8 weeks of HDM aeroallergen exposure, infant monkeys exhibited a significant reduction in the total peripheral blood lymphocyte numbers and a decreased frequency of peripheral blood CD4+ T lymphocytes with a CD45RA-'memory' immunophenotype. Lavage CD4+ T lymphocytes from HDM-exposed monkeys showed elevated expression of CD25, as well as an increase in CD45RA-/CD62L-/CD11ahigh immunophenotype. Eosinophils were more abundant within airways of HDM-exposed monkeys, accumulating maximally within the trachea.

CONCLUSION

These data demonstrate the development of immunological responses following chronic inhalation of a common environmental allergen during postnatal maturation in the non-human primate.

In utero priming of allergen-specific helper T cells

BACKGROUND

Allergic diseases are major health problems in developed countries. Cord blood mononuclear cells (CBMC) at birth can proliferate after stimulation with allergen and this has led to the widespread view that the sensitization of the fetal immune system by allergens is a key determinant in establishing immunological bias towards allergy. However, the notion that the immune system can be primed by allergen in utero remains unproven. Determination of the CD45 isoform of responding T helper cells is an established method of determining the activation status of responding T helper cells because unsensitized cells express CD45RAhigh and previously sensitized cells CD45ROhigh.

OBJECTIVE

To determine if sensitization of allergen-specific T helper cells can occur in utero by determining the CD45 isoform of CBMC proliferating in response to allergen.

METHODS

CBMC proliferative responses were measured after stimulation in culture with a panel of allergens, mitogen and control antigen. To ascertain whether any responding T helper cells had been primed in utero, depletion experiments established whether they carried the CD45ROhigh marker of previous activation or the CD45RAhigh marker of unstimulated T cells.

RESULTS

CBMC from a high proportion of 223 randomly selected neonates were stimulated to proliferate in vitro by allergens, with 76% responding to timothy grass pollen. In 50% of such responses to timothy grass, the CD45 isoform of the T cells that proliferate indicated that they had been previously activated. However, the remaining 50% of responses to timothy grass were mediated by previously unstimulated T cells. Proliferative responses mediated by CBMC sensitized in utero tended to be greater in magnitude than those mediated by unsensitized cells (P = 0.08). Seventy-five per cent of CBMC samples proliferated after stimulation with mycobacterial PPD and, as in BCG-vaccinated adults, all such CBMC proliferative responses at birth were predominately mediated by sensitized cells.

CONCLUSION

Allergen- and antigen-specific Th cells can be primed in utero.

Lymphoproliferative responses in cord blood and at one year: no evidence for the effect of in utero exposure to dust mite allergens

BACKGROUND

Maternal allergen exposure beyond the 22nd week of pregnancy may be important in foetal T cell priming. Allergen-specific cord blood mononuclear cell (CBMC) immunoproliferative responses without corresponding bacterial antigen responses (tetanus toxoid), have been suggested as evidence of in utero sensitization.

OBJECTIVES

To investigate the relationship between lymphoproliferative responses at birth and at 1 year with maternal and 1-year infants house dust mite allergen exposure.

METHODS

Home visits and dust sampling were performed by the 20th week of pregnancy, immediately after birth, and then at 1 years of age. Der p 1 was assayed using a two-site immunometric ELISA. CBMC immunoproliferative responses (AIM V serum-free medium; 1 x 105 cells/well) were measured for 225 neonates (171 had a high risk of atopy (HR)--both parents skin test positive; 59 had a low risk of atopy (LR) - both parents skin test negative, no history of atopy) by 3H-Thymidine (1microCi/well) incorporation after stimulation in primary culture with phytohaemagglutinin (PHA) (1 microg/mL), house dust mite [HDM] extract (30 microg/mL), immunopurified Der p 1 (30 microg/mL), Tetanus toxoid (TT) (aluma free, 30 Lf/mL) or vehicle. Blood was collected from 144 infants at the age of 1 years and stimulated proliferative responses were assessed using the same procedure.

RESULTS

PHA-stimulated lymphoproliferative response was significantly lower in HR compared to LR neonates (mean difference 38%, 95% CI 15%-54%; P = 0.003); significantly lower proportion of positive CBMC responses to HDM occurred in LR than in HR neonates (30.4% vs. 46.6%; P = 0.034). There was no relationship between Der p 1 levels in maternal bed and CBMC immunoproliferative responses, despite the 21 000-fold range of maternal Der p 1 exposure. No significant differences in magnitude, or in proportion of positive responses to any stimulant were observed between the neonates at low, medium or high tertile of allergen exposure. Immunoproliferative responses at birth were not predictive of 1-year PBMC responses. There was no relationship between maternal allergen exposure in pregnancy and 1-year PBMC proliferative responses. However, the proportion of positive proliferative responses at 1 years significantly increased with increasing infant Der p 1 exposure at 1 years.

CONCLUSION

These results indicate that the magnitude of immunoproliferative responses are unrelated to maternal mite allergen exposure and cannot be used as evidence for in utero sensitization to inhalant allergens. The immunoproliferative responses at 1 year seem to shift away from the genetically influenced responses at birth towards responses to specific stimulants which correlate with environmental exposure to those specific stimulants. These data support the concept of sensitization to inhalant allergens occurring in early life, but not in utero.

Two-color flow cytometric analysis of preterm and term newborn lymphocytes

Immune system maturation proceeds postnatally in humans. Therefore, newborns, especially those of a lower gestational age, are not fully immunocompetent and are more likely to acquire perinatal infections. In order to investigate the neonatal immune system status, the major lymphocyte subpopulations were studied in newborns of different gestational age, comparing term newborns and adults. The cord blood from 66 newborns and the peripheral blood from 23 adults were analyzed using fluorochrome labelled monoclonal antibodies and two-color flow cytometry. The newborns were divided into three groups according to their gestational age. Ten prematures were under 32 weeks of gestation, 35 were of 32-37 weeks and there were 21 term newborns. The percentage of cytotoxic T lymphocytes (CD4 CD8+) was lower in term newborns as compared to the adult controls (17.8 versus 30.3%), and so were the percentages of activated T lymphocytes (CD3+Ia+; 0.3 versus 3.7%), cytotoxic non-MHC restricted T lymphocytes (CD3+CD16+CD56+; 0.2 versus 1.8%) and NK cells (CD3-CD16+CD56+; 4.8 versus 15.5%). On the contrary, the proportions of unlabelled cells were increased in term cord blood. The expression of CD45R0 marker on neonatal lymphocytes was very low (1%). In comparison to the higher-gestation newborns, the lower gestation prematures had reduced percentages of T lymphocytes (CD3+; 43 versus 65%), mostly helper T lymphocytes (CD4+CD8-; 35 versus 50%), and increased percentages of unlabelled cells. The percentages of NK cells (CD3+CD16+CD56+) and B lymphocytes (CD3-CD19+; CD3-Ia+) did not differ among the tested newborn groups. There were no significant differences in major lymphocyte subpopulations between the group of highest-gestation prematures and the group of term newborns that differed significantly when compared to adults. The lowest-gestation newborns showed the most immature lymphocyte phenotype with the highest percentages of unlabelled cells.

Determination of T-cell subpopulations and intracellular cytokine production (interleukin-2, interleukin-4, and interferon-gamma) by cord blood T-lymphocytes of neonates from atopic and non-atopic parents

This report describes the results of a prospective study on immunological markers in cord blood for the prediction of allergic diseases in children. First we evaluated methodological aspects of the flow cytometric technique on cord blood cytokine measurements. Subsequently, the T-cell subsets and percentage of cytokine-producing cord blood T-helper (Th) and T-suppressor/cytotoxic lymphocytes of neonates from atopic and non-atopic parents were compared. A group of 33 healthy, full-term newborn infants of whom 23/33 were at risk for atopy (i.e. having at least one parent with one or more atopic symptoms and positive specific immunoglobulin E [IgE] to at least one common inhalant allergen) was studied. A flow cytometric technique was used to analyze cord blood T-cell subsets and to determine the percentage of interleukin (IL)-2-, IL-4-, and interferon-gamma (IFN-gamma)-producing cord blood Th and T-suppressor/cytotoxic lymphocytes following stimulation with phorbol 12-myristate 13-acetate (PMA) and ionomycin. The percentage of CD3 (T lymphocytes), CD3+ CD4+ (Th lymphocytes), CD3+ CD8+ (T-suppressor/cytotoxic lymphocytes), CD19+ (B lymphocytes), CD3+ CD4+ CD45RO+ (memory Th lymphocytes), and CD3+ CD4+ CD45RA+ (naive Th lymphocytes) cells was unrelated to parental atopic status. PMA stimulation augmented the percentage of IL-2- and IFN-gamma-producing Th and T-suppressor/cytotoxic lymphocytes, whereas the number of IL-4-producing T lymphocytes remained very low or undetectable. No differences in the percentage of TL-2-, IL-4- and IFN-gamma-producing Th and T-suppressor/cytotoxic lymphocytes were found between neonates from atopic and non-atopic parents. These results will be re-evaluated when the atopic status of the children at the age of 1 and 2 years can be assessed.

Normal immune responses to ingested foods

This is a short review of the literature with a bias toward the author's work. Small amounts of dietary antigens are taken up into the circulation. B-cell responses to foods (antibodies and antibody-secreting cells) occur as a physiological event locally and in the circulation in all three major immunoglobulin classes. A low levels of IgE is also a normal phenomenon. IgA anti-gliadin antibodies represent an exception. Antibody titers in general tend to decline with age. T-cell responses specific for foods are low in the circulation of healthy subjects. T-cell cytokines are more frequently produced in the gastrointestinal mucosa compared with the circulation. Results indicate that the phenomenon of oral tolerance takes place in humans. Oral tolerance within the T cell system may represent an important regulatory mechanism for normal immunity.

Can we predict which wheezy infants will continue to wheeze?

Early intervention strategies in infant wheezing will be dependent on the ability to predict persistence of disease. We undertook a prospective longitudinal study to determine which factors might be predictive for the persistence of wheeze. We examined a group of 107 children 3 to 36 mo of age with at least one atopic parent. Children were recruited within 12 wk of first wheeze. Factors assessed included: personal atopy (IgE > 1 SD above age-related normal and/or eczema and/or positive skin tests); parental atopy; number of siblings; age at first wheeze; sex; serum-soluble IL-2R; proliferation of peripheral blood mononuclear cells (PBMC) to beta-lactoglobulin and to D. pteronyssinus; production of IFN-gamma on stimulation of PBMC with beta-lactoglobulin and with D. pteronyssinus. A positive clinical outcome (child requiring prophylactic antiasthma treatment after 1 yr) was observed in 53 (49.5%) children. Predictor variables were assessed by univariate and multivariate logistic regression. Wheeze was more likely to be persistent in older, atopic children with biparental atopy. The model offering best prediction of persistent wheeze with least risk of including asymptomatic subjects was age at presentation + sIL-2R. Trials of early intervention strategies using a logistic regression equation based on this model for patient recruitment can now be designed.

Respiratory symptoms and duration of residence in immigrant teenagers living in Melbourne, Australia

OBJECTIVE

Examination of the relation between respiratory symptoms and time since arrival in Australia in immigrant teenagers living in Melbourne.

DESIGN

Two stage, stratified, cross sectional survey.

SETTING

High schools (n = 51).

SUBJECTS

9794 people aged 13-19 years.

MAIN OUTCOME MEASURES

Prevalence of wheeze during a 12 month period, region of birth, duration of residence in Australia.

RESULTS

The estimated population 12 month period prevalence of wheeze was 18.9% (95% confidence interval (CI), 18.0 to 19.9). In subjects born outside Australia, residence for five to nine years in Australia was associated with a 2.1-fold (CI, 1.1 to 4.0) increase in the odds of self reported wheeze; after 10-14 years, this risk increased 3.4-fold (CI, 1.8 to 6.7). There was no difference in severity of wheeze, measured by reported frequency of attacks, between Australian born and non-Australian born subjects.

CONCLUSIONS

The notion of a continued secular increase in the prevalence of wheezing is not supported. There is a time dose effect on the prevalence of symptoms in subjects born outside Australia and now living in Melbourne, which is independent of age and country of birth.

Is childhood asthma an inflammatory disease?

There is now extensive evidence that asthma results from inflammation in large and small airways, and that the degree of inflammation reflects the clinical severity of the disease. Most of this evidence, however, has come from studies in adult patients. Evidence in children comes largely from indirect studies such as measurements of peripheral blood cells and inflammatory markers, rather than from direct bronchoscopic examination. Studies in adults show that inflammation in asthma is characterized by eosinophilia, epithelial damage, and bronchial hyperresponsiveness, and that activation of allergen-specific T cells plays an important role in orchestrating the inflammatory process. In children, indirect evidence of inflammation comes from the observation that anti-inflammatory agents such as inhaled corticosteroids improve symptoms and bronchial hyperresponsiveness, reduce the number of asthma exacerbations, and limit the progressive decline in lung function. Further evidence comes from measurements of nitric oxide and hydrogen peroxide (potential inflammatory markers) in exhaled air, and of inflammatory mediators in plasma and urine. As in adults, there is evidence that lymphocytes play an important role in orchestrating the inflammatory process. The immunologic profile appears to shift from a Th1-type cytokine profile to an allergen-related Th2-type profile prior to birth. Such a Th2 predominance constitutes a risk factor for the subsequent development of bronchial hyperresponsiveness and asthma in response to allergen.

Peripheral blood T and B lymphocyte subpopulations in infants with acute respiratory syncytial virus brochiolitis

Most data concerning immunopathogenetic mechanisms involved in respiratory syncytial virus (RSV) infection are derived from animal studies. In infants with RSV bronchiolitis the target organ i.e. the airway is hard to explore. We looked for specific alterations in peripheral blood lymphocyte subpopulations in infants hospitalized for RSV bronchiolitis. Flow cytometric analysis with a large panel of monoclonals was performed on peripheral blood lymphocytes in thirty-two infants (mean age: 4.9 months) admitted for RSV bronchiolitis. Data collected on admission were compared with age-matched control values and also with results obtained at the end of the first week of hospitalization. Differences between age-groups (older or younger than 4 months) and between clinical subgroups (clinical severity score more or less than 6) were looked for. In the group of infants as a whole, regardless of age and clinical score the number of CD4+ cells on admission was significantly elevated compared to normal values for age (p<.0001) including a high fraction of the naive suppressor-inducer subpopulation (CD4+/CD45RA+) and a low fraction of the reciprocal memory helper-inducer subpopulation (CD4+/CD29+). Within the CD8+ cell population the number of T cells with cytotoxic activity (CD8+/S6F1+) was significantly elevated (p<.0001) as were other types of cytotoxic cells. A significant decrease (p<.0001) in the proportion of the precursor/suppressor-effector subpopulation (CD8+/S6F1-) was seen. Absolute numbers and percentages of CD19+ B cells were significantly elevated (p<.0001) with a significant increase in the CD5+ subfraction (p<.0001) as well as in the CD10+ subfraction (p<.0001). In the older age group immunophenotypic cytotoxicity was more pronounced with increased clinical score. During recovery the CD45RA+:CD29+ ratio tended to normalize within the CD4+ T cells. Within the B lymphocyte subsets significant increase in the CD19+/CD5+ fraction (p<.05) was seen. We conclude that there are significant changes in the number of peripheral blood lymphocyte subsets in infants with RSV bronchiolitis as compared to age-related controls. We hope that present data could be useful in further exploration of RSV immunology in humans. A possible link between RSV bronchiolitis and the subsequent development of atopy is mentioned.

Prenatal origins of asthma and allergy

The prevalence of asthma and related allergic disorders has increased considerably over the last 25 years. Genetic stock has not changed, so environmental factors must have influenced the phenotype. Infants who develop allergy already have an altered immune response at birth. We have investigated the development of immune responses during gestation and the effect of maternal allergen exposure during pregnancy and infant exposure in the first month of life on the development of allergy and disease. There was higher specific peripheral blood mononuclear cell proliferation to house dust mite (P = 0.01) and birch pollen (P = 0.004) in the third trimester compared with the second trimester, with the first positive responses seen at 22 weeks gestation. Maternal exposure to birch pollen after 22 weeks resulted in higher (P = 0.005) infant peripheral blood mononuclear cell responses to birch pollen at birth. Infants born at term, with at least one atopic, asthmatic parent, who developed allergic symptoms and positive skin prick test by one year of age had raised proliferative responses to house dust mites at birth compared to those with no symptoms (P = 0.01). In genetically predisposed individuals, antenatal factors, including maternal and thereby fetal exposure to allergens and maternoplacental-fetal immunological interactions, are active in determining whether an allergic predisposition is manifested as disease.

Fetal peripheral blood mononuclear cell proliferative responses to mitogenic and allergenic stimuli during gestation

Blood samples were obtained from fetuses and premature babies (n = 51) (15-34 weeks gestation) to determine at what stage the fetal immune system was able to produce a positive proliferative response to common allergens. Peripheral blood mononuclear cells (PBMC) were stimulated with the mitogen, phytohaemagglutinin (PHA), and the allergens, house dust mite, cat fur, birch tree pollen, beta-lactoglobulin, ovalbumin and bee venom (mellitin). Results were expressed as ratios of stimulated to unstimulated 3H thymidine incorporation, and as percent positive responders. There was an increase in proliferation ratio which correlated with increasing gestational age for PHA (p < 0.0001), cat fur (p = 0.042), birch pollen (p = 0.022) and beta-lactoglobulin (p = 0.006). The point in gestation when cells from some individuals began responding to the allergens with a ratio of 2.0 was at approximately 22 weeks. PBMC proliferative response ratios were higher from samples from babies > 22 weeks gestation compared to < 22 weeks for the mitogen and all allergens, except mellitin. There was also a greater proportion of positive responders from samples > 22 weeks compared to < 22 weeks for the mitogen and all allergens, except mellitin. Maternal exposure to birch pollen, which has a discrete season, was assessed to determine whether exposure had occurred at 22 weeks gestation or beyond. Results showed a higher proliferative response in infant cells stimulated with birch pollen (p = 0.005) and higher proportion of positive responders (p = 0.01) in the group of babies whose mothers had been exposed to birch pollen beyond 22 weeks, compared to those whose mothers had not been so exposed. These results suggest that in utero fetal exposure to an allergen from around 22 weeks gestation may result in primary sensitisation to that allergen, leading to positive proliferative responses, at birth.