Immune activation during infancy in healthy humans

First molecular approach to diagnose paediatric pulmonary lophomoniasis: A case series

A prospective study was conducted from 2017 to 2021 at Bouali Hospital in Mazandaran province, Sari, Iran. Out of 58 patients who were enrolled in our study, lophomoniasis was diagnosed in bronchoalveolar lavage fluid of nine patients, for the first time, using an in‐house polymerase chain reaction technique. All patients were treated with metronidazole at 7.5 mg/kg/day every 12 h for 14 days. After 6 months of follow‐up, symptoms were fully resolved.

Clinical value of fecal calprotectin

Inflammatory bowel disease (IBD) denotes a group of chronic incurable disorders characterized by relapsing-remitting inflammation of the gastrointestinal tract. IBD represents a growing global burden with a prevalence exceeding 0.3% in the Western world and an accelerating incidence in newly industrialized countries. The target for treating IBD has shifted in recent years from symptom control to mucosal healing (MH), which has been shown to be associated with favorable long-term outcomes. The gold standard for ascertaining MH is endoscopic assessment, but endoscopy is limited by its invasive nature, high cost, and finite availability. Surrogate biomarkers are therefore of great utility. Calprotectin, a cytosolic protein derived predominantly from neutrophils, is now widely used in this capacity. Calprotectin is found in various bodily fluids at concentrations proportional to the degree of inflammation, including in feces at levels roughly six times higher than in the blood. Fecal calprotectin (FCP) therefore reflects intestinal inflammation. Various assays, including point-of-care and home-based tests, are now available for measuring FCP. FCP is used for screening purposes, to aid in distinguishing inflammatory from non-inflammatory gastrointestinal conditions like irritable bowel syndrome (IBS), as well as in the monitoring of known IBD. The aims of this review are to provide an overview of the methods used to measure FCP and to review the evidence supporting the use of FCP in IBD, particularly as it pertains to screening, monitoring and predicting disease relapse.

Fecal Calprotectin

Calprotectin is a 36kDa member of the S100 family of proteins. It is derived predominantly from neutrophils and has direct antimicrobial effects and a role within the innate immune response. Calprotectin is found in various body fluids in proportion to the degree of any existing inflammation and its concentration in feces is about six times that of plasma. Measurement of fecal calprotectin is a useful surrogate marker of gastrointestinal inflammation. It has a high negative predictive value in ruling out inflammatory bowel disease (IBD) in undiagnosed, symptomatic patients and a high sensitivity for diagnosing the disease making it useful as a tool for prioritising endoscopy. In patients with known IBD, fecal calprotectin can be a useful tool to assist management, providing evidence of relapse or mucosal healing to enable therapy to be intensified or reduced. There are a number of commercial calprotectin assays with marked difference in performance as judged by external quality assessment and at present no standardised reference material exists. Various factors may affect results including age, medication and day to day variation. Laboratories should therefore be mindful of the characteristics of their own assay and factors that may affect results.

Influence of breastfeeding versus formula feeding on lymphocyte subsets in infants at risk of coeliac disease: the PROFICEL study

PURPOSE

In addition to genetic risk, environmental factors might influence coeliac disease (CD) development. We sought to assess the effect of the interaction between milk-feeding practices and the HLA-DQ genotype on peripheral lymphocyte subsets and their activation markers in infants at familial risk for CD.

METHODS

170 newborns were classified in 3 different genetic risk groups (high risk, HR; intermediate risk, IR; and low risk, LR) after DQB1 and DQA1 typing. Lymphocyte subsets were studied at the age of 4 months by flow cytometry analysis.

RESULTS

79 infants were receiving exclusive breastfeeding (BF) and 91 partial breastfeeding or formula feeding (FF). Regarding genetic risk, 40 infants were classified in HR group, 75 in IR group and 55 in LR group. Two-way ANOVA did not show significant interactions between the type of milk feeding and genetic risk group on the lymphocyte subsets analysed. One-way ANOVA for milk-feeding practice alone showed that the percentage of CD4 + CD25+ cells was significantly higher in BF group than in FF group (BF, 10.92 ± 2.71; FF, 9.94 ± 2.96; p = 0.026), and absolute counts of CD4 + CD38+ cells were significantly higher in FF group than in BF group (FF, 2,881.23 ± 973.48; BF, 2,557.95 ± 977.06; p = 0.038). One-way ANOVA for genetic risk alone showed that absolute counts of NK cells were significantly higher in IR group than HR and LR groups (IR, 539.24 ± 340.63; HR, 405.01 ± 239.53; LR, 419.86 ± 262.85; p = 0.028).

CONCLUSION

Lymphocyte subset profiles in the early stages of life could be modulated by milk-feeding practices and genetic risk separately. Breastfeeding might have a positive immunomodulatory effect on lymphocyte subsets in infants at risk of CD.

Evaluation of faecal calprotectin as a valuable non-invasive marker in distinguishing gut pathogens in young children with acute gastroenteritis

AIM

The aim of the study is to evaluate faecal calprotectin (f-CP) in children ≤3 years of age with acute gastroenteritis (AG) as an early predictor of bacterial inflammation.

METHODS

We prospectively analysed f-CP levels and diagnostic workup in 107 consecutive children (66 AG, 41 controls).

RESULTS

Children with bacterial AG (BAG) was found to have higher diarrheal frequency (p < 0.01), fever (p < 0.01), erythrocyte sedimentation rate (p < 0.001), white blood count (p < 0.01) and C-reactive protein (CRP) (p < 0.001) compared with viral AG (VAG). Vomiting was frequent in VAG (p < 0.001). f-CP negatively correlated with age in controls (r = -0.5998). BAG demonstrated significantly higher f-CP levels [median, 219 μg/g, interquartile range (IQR): 119-350.2] compared with VAG (49.3 μg/g, IQR: 8.8-131.1) as well as controls (26.5 μg/g, IQR: 14.9-55.1) (p < 0.001). VAG and control f-CP levels were similar. f-CP was the best-rated marker of BAG with a diagnostic accuracy of 92%. Receiver-operator characteristic analysis revealed an area under curve of 0.95 for identifying BAG; sensitivity and specificity of f-CP were 93% and 88%, respectively, at an adjusted cut-off point of 103.9 μg/g faeces. Combined f-CP and CRP yield improved diagnostic accuracy of 94% for BAG.

CONCLUSION

f-CP facilitates early discrimination between bacterial and viral causes of AG in young children. Combining f-CP with CRP increases the diagnostic power of diagnosing BAG.

Crypt fission peaks early during infancy and crypt hyperplasia broadly peaks during infancy and childhood in the small intestine of humans

BACKGROUND

Postnatal growth of the small intestine occurs by crypt hyperplasia and by the less recognised mechanism of crypt fission. How the small intestine grows is largely extrapolated from animals and is poorly described in humans.

AIM

To investigate crypt fission and crypt hyperplasia as mechanisms of intestinal growth in humans.

PATIENTS AND METHODS

Proximal intestinal samples were taken from 3 neonates at surgical anastomosis, and duodenal biopsies were taken at endoscopy from 16 infants (mean age 0.7, range 0.3-1.7 years), 14 children (mean age 7.9, range 2.4-16.2 years), and 39 adults. Morphometric measures of villous area, crypt length (measure of crypt hyperplasia), and percentage of bifid crypts (measure of crypt fission) were assessed by a microdissection technique.

RESULTS

Mean crypt fission rates in neonates, infants, children, and adults were 7.8%, 15%, 4.9%, and 1.7%, respectively. In particular, crypt fission peaked at 18% in 5 infants from 6 to 12 months of age. Mean crypt length was 123 microm in neonates, 287 microm in infants, 277 microm in children, and 209 microm in adults. Thus, crypt hyperplasia had a broad peak during infancy and childhood.

CONCLUSIONS

We conclude that crypt fission was present predominantly during infancy, and crypt hyperplasia occurred during both infancy and childhood.

Fecal calprotectin in very low birth weight infants

OBJECTIVES

To measure concentrations of fecal calprotectin (f-calprotectin) in infants with very low birth weight (VLBW; <1500 g) longitudinally and to describe changes in f-calprotectin in infants who develop severe abdominal disease.

PATIENTS AND METHODS

The study included 59 VLBW infants. Seven patients (disease group) developed severe abdominal disease defined as necrotizing enterocolitis (NEC) or a condition leading to laparotomy. The remainder (n = 52) were considered reference infants and had a mean (+/-SD) gestational age of 27.2 +/- 2.6 weeks and a birth weight of 939 +/- 273 g. F-calprotectin was analyzed in meconium and weekly during postnatal weeks 1 to 8. In disease cases, more frequent samples were analyzed around the time of abdominal disease diagnosis.

RESULTS

In reference infants the median (range) f-calprotectin level in meconium was 332 (12-9386) microg/g and correlated negatively to Apgar score. F-calprotectin in postmeconium samples was 253 (9-1867) microg/g and correlated positively to delivery by cesarean section, postnatal age, and volume of enteral feeds, and negatively to treatment with antibiotics and corticosteroids. In reference infants no postmeconium sample had f-calprotectin levels >2000 microg/g. In disease cases f-calprotectin was increased to >2000 microg/g in 3 cases of NEC and 1 case of covered perforation with microscopic bowel inflammation. In 1 case of NEC without microscopic bowel inflammation and 2 cases of focal intestinal perforation, f-calprotectin levels never exceeded 2000 microg/g.

CONCLUSIONS

F-calprotectin concentrations in VLBW infants are similar to previously reported levels in healthy term and moderately preterm infants. An f-calprotectin level >2000 microg/g is a useful but not an early marker of NEC and other severe intestinal inflammatory conditions in VLBW infants.

Diabetes-prone BioBreeding rats do not have a normal immune response when weaned to a diet containing fermentable fibre

Diet is known to modulate the development of diabetes in diabetes-prone BioBreeding (BBdp) rats. The objective of the present study was to determine the effect of fermentable fibre (FF) on immune function in BBdp and diabetes-resistant BioBreeding (BBdr) rats after weaning. Weanling BBdp (thirty-six to thirty-eight per diet) and BBdr rats (thirty to thirty-two per diet) were fed a nutritionally complete, semi-purified, casein-based diet containing either cellulose (control diet, 8 % w/w) or FF (3·2 % cellulose+4·8 % w/w inulin). At 35 d, the small intestine was excised and lymphocytes isolated from spleen, mesenteric lymph nodes and Peyer's patches. Feeding FF to both BBdr and BBdp rats affected the production of anti-inflammatory cytokines (P=0·02). In BBdr rats, feeding FF compared with cellulose resulted in an increased small intestinal length (P=0·0031), higher proliferative (stimulation) index from both splenocytes (P=0·001) and mesenteric lymph nodes (P=0·04), and an increased proportion of CD8+ T-cells in the Peyer's patches (P=0·003). We did not observe an effect of diet on the number of IgA-bearing cells in the jejunum from BBdr rats. Feeding FF to BBdp rats did not affect the same parameters. BBdp rats had both a higher proportion of B-cells in the Peyer's patches (P=0·01) and a higher number of IgA+ cells in the jejunum (P=0·0036) when fed a diet containing FF, a response not observed in BBdr rats. We demonstrate that several aspects of the BBdp immune system respond differently than that of BBdr rats when challenged at weaning with FF.

Postnatal epithelial growth of the small intestine in the rat occurs by both crypt fission and crypt hyperplasia

Studies of growth of the small intestine have largely concentrated on crypt hyperplasia rather than crypt fission. The aim of this study was to investigate quantitatively both crypt fission and crypt hyperplasia. DAxPVG/c rats were killed at 7, 11, 14, 17, 19, 21, 25, 55, and 72-73 days of life. Samples of jejunum at one third of the intestinal length were taken for morphometry (villous area, crypt area, percentage of bifid crypts, and crypt mitotic count) by microdissection. Growth factors and their receptors were assessed by oligonucleotide microarray. Crypt fission was 10.5%, 5.2%, and 1.5% at days 11, 25, and 72-73 of life, respectively. Crypt hyperplasia increased from day 21. No conventional growth factor was identified during crypt fission. We conclude that crypt fission contributes to growth of the small intestine prior to weaning and crypt hyperplasia to growth after weaning.

Health risks of enteric viral infections in children

Children are at a greater risk of infections from serious enteric viral illness than adults for a number of reasons. Most important is the immune system, which is needed to control the infection processes. This difference can lead to more serious infections than in adults, who have fully developed immune systems. There are a number of significant physiological and behavioral differences between adults and children that place children at a greater risk of exposure and a greater risk of serious infection from enteric viruses. Although most enteric viruses cause mild or asymptomatic infections, they can cause a wide range of serious and life-threatening illnesses in children. The peak incidence of most enteric viral illnesses is in children <2yr of age, although all age groups of children are affected. Most of these infections are more serious and result in higher mortality in children than adults. The fetus is also affected by enterovirus and infectious hepatitis resulting in significant risk of fetal death or serious illness. In addition to the poliovirus vaccine, the only vaccine available is for hepatitis A virus (HAV). A vaccine for rotavirus has currently been withdrawn, pending review because of potential adverse effects in infants. No specific treatment is available for the other enteric viruses. Enteric viral infections are very common in childhood. Most children are infected with rotavirus during the first 2yr of life. The incidence of enteroviruses and the viral enteric viruses ranges from 10% to 40% in children and is largely dependent on age. On average, half or more of the infections are asymptomatic. The incidence of hepatitis A virus is much lower than the enteric diarrheal viruses. There is no current evidence for hepatitis E virus (HEV) acquisition in children in the U.S. Enteric viral diseases have a major impact on direct and indirect health care costs (i.e., lost wages) and amount to several billion dollars a year in the U.S. Total direct and indirect costs for nonhospitalized cases may run from $88/case for Norwalk virus to $1,193/case for enterovirus aseptic meningitis. Direct costs of hospitalization ran from $887/case for Norwalk virus to $86,899/case for hepatitis A. These costs are based on 1997-1999 data. Generally, attack rates during drinking water outbreaks are greater for children than adults. The exception appears to be hepatitis E virus where young adults are more affected. However, pregnant women suffer a high mortality, resulting in concurrent fetal death. Also, secondary attack rates are much higher among children, probably because of fewer sanitary habits among this age group. Overall, waterborne outbreaks of viral disease have a greater impact among children than adults. To better quantify the impact on children, the literature hould be further reviewed for case studies of waterborne outbreaks where data are available on the resulting illness by age group. The EPA and/or Centers for Disease Control should attempt to collect these data as future outbreaks are documented.

Activation of the gut-associated lymphoid tissue with expression of interleukin-2 receptors that peaks during weaning in the rat

BACKGROUND

Weaning exposes the intestinal mucosa to food and bacterial antigens at an age when the immune system is believed to be immature and functionally defective. The purpose of this study was to investigate changes in activation and phenotype of immune cells of the gut-associated lymphoid tissue during weaning.

METHODS

Litters of infant rats were studied from pre- to postweaned life. The activation status, assessed by interleukin-2 receptor (IL-2R) expression, and phenotype of cells in the gut-associated lymphoid tissue were examined by immunostaining.

RESULTS

Interleukin-2 receptor expression peaked two to four-fold at midweaning (day 21) in mesenteric lymph nodes, jejunal lamina propria, Peyer's patches, and intraepithelial lymphocytes, compared with adult animals (day 70). CD45+ cells expanded in the lamina propria, epithelium, and lymphocyte-filled villi. With CD45 as the denominator, 10% to 50% of lymphocytes in the lamina propria and epithelium were alphabetaT-cell receptor (TCR)+, but the remaining cells had a null phenotype, because there were low numbers of gammadeltaTCR+ T cells, B cells, and macrophages. Natural killer cells peaked at midweaning in the lamina propria (9%) and epithelium (20%) but were less than 5% of CD45+ cells after weaning.

CONCLUSIONS

Rather than being immature or functionally inactive, the gut-associated lymphoid tissue reacts appropriately during weaning with expression of IL-2R and expansion of alphabetaTCR+ T-cells.

The influence of initial exposure timing to beta-lactoglobulin on oral tolerance induction

BACKGROUND

Although a number of studies have investigated the induction of oral tolerance to several proteins, relatively little is known about the induction of oral tolerance to beta-lactoglobulin, one of the major antigenic proteins in milk.

OBJECTIVE

We investigated the influence of the timing of the initial beta-lactoglobulin exposure on oral tolerance induction and examined some characteristics of the tolerogenic immune response.

METHODS

BALB/c mice were given beta-lactoglobulin prenatally or from the third or fifth postnatal week, bred for 17 weeks, and compared with unexposed control mice. Specific plasma anti-beta-lactoglobulin antibodies (total IgG, IgG subclasses, IgM, and IgE), antigen-specific splenocyte responses, frequencies of antibody-producing cells, and cytokine production by splenocytes, intestinal mucosal lymphocytes, and Peyer's patches were analyzed.

RESULTS

Differences were observed among the 4 groups of mice in changes of plasma anti-beta-lactoglobulin antibody titers, antigen-specific T-cell proliferation, and frequencies of antibody-producing splenocytes, intestinal mucosal lymphocytes, and Peyer's patch cells after the first exposure to beta-lactoglobulin. The onset and duration of the immunologic responses were found to be dependent on the timing of antigen exposure. Prenatal exposure to antigen facilitated the induction of oral tolerance to beta-lactoglobulin, whereas delayed antigen exposure retarded tolerance. The induction of oral tolerance was associated with increased IL-4 and/or IL-10 production and decreased IL-12 production.

CONCLUSION

Our results suggest that the timing of initial antigen exposure greatly influences the induction of oral tolerance to beta-lactoglobulin and that altered secretion of regulatory cytokines may be responsible for the differences in antibody production and oral tolerance induction.

Adipose tissue in human infancy and childhood: an evolutionary perspective

Humans diverge from most mammals, including nonhuman primates, by depositing significant quantities of body fat in utero and are consequently one of the fattest species on record at birth. While explanations for the fat layer of human neonates have commonly assumed that it serves as insulation to compensate for hairlessness, empirical support for this hypothesis is presently weak. Whether the tissue's abundance at birth and growth changes in adiposity during infancy and childhood might be explained in light of its role as energy buffer has not been assessed, and this possibility is explored through development of a model of fat function and growth centered on two related hypotheses. The first is that the greater adiposity of human neonates is at least partially explainable as an accompaniment of the enlarged human brain, which demands a larger energy reserve to ensure that its obligatory needs are met when the flow of resources from mother or other caretakers is disrupted. The second is that age-related changes in the likelihood of experiencing such disruption have influenced the pattern of investment in the tissue, reflected today in peak adiposity during infancy and a decline to a leaner childhood period. Nutritional disruption is common at birth and until lactation is established, during which time human newborns survive from fats deposited prenatally, suggesting one possible explanation for the early onset of fat deposition. At weaning, the transition from breast milk to supplemental foods and the parallel transition from maternal to endogenous immune protection interact to increase the frequency and impact of nutritional disruption, and this may help explain why newborns devote roughly 70% of growth expenditure to fat deposition during the early postnatal months. Evidence is presented that fat stores are mobilized during infections, hinting at one possible mechanism underlying the association between nutritional status and infectious morbidity and mortality among infants in nutritionally stressed human populations. Consistent with the proposed hypothesis, well-fed infants acquire peak fat reserves by an age of peak prevalence of malnutrition, infectious disease, and fat reserve depletion in less-buffered contexts, and childhood--characterized by minimal investment in the tissue--is a stage of reduced risk of energy stress. The model presented here foregrounds energy storage in adipose tissue as an important life-history strategy and a means to modify mortality risk during the nutritionally turbulent period of infancy.

Interleukin 2 receptor regulation and IL-2 function in the human infant

IL-2 receptor is expressed at low levels on adult blood lymphocytes, and at lower levels on cord blood cells. IL-2 receptor alpha and beta chain expression increases gradually from 0-18 months of age. The level of soluble CD25 (IL-2 receptor alpha chain) has been reported to be elevated in cord blood. Quantitative RT-PCR showed that adult cells express 10 times as much CD25 mRNA as cord cells. Cord plasma showed only a marginal ability to strip CD25 from the membrane. To assess the functional consequences of low IL-2 receptor expression, cord and adult cells were activated in vitro. The response was stimulus-dependent, but cord cells upregulated CD25 readily. Cord and adult cells proliferated in an IL-2-dependent assay to a similar extent. Infants suffering acute infection showed marginally higher levels of membrane CD25 expression than infants without overt infection. Thus neonatal and infant lymphocytes express lower levels of IL-2 receptors than adult cells, reflecting lower mRNA concentrations at least for CD25; they are able to up-regulate receptors in response to in vitro stimulation and are able to respond in vitro to IL-2-dependent stimulation; however in vivo there may be a dampening down of the IL-2 system in infancy.

Transforming growth factor-beta levels in maternal milk and expression in postnatal rat duodenum and ileum

After birth, the gastrointestinal tract of the neonate is exposed to food and bacterial and environmental antigens. Maternal milk components may play a role in regulation of mucosal immune activity to luminal antigens. In this study we determine the ontogeny of transforming growth factor (TGF)-beta1-producing cells in the rat pup small intestine and assess maternal milk concentrations of TGF-beta. Intestinal tissue samples of duodenum and ileum were collected, processed, and stained for TGF-beta1, and in situ hybridization for TGF-beta1 mRNA was also performed on the duodenum. TGF-beta levels in milk were assayed by ELISA. TGF-beta2 levels in milk were high at d 6, and declined thereafter at d 10 and 19. TGF-beta1 was not detected. In contrast, the cell number and intensity of staining of TGF-beta1 peptide in the small intestine was low in 3- and 10-d-old rats and increased markedly by 19 d of life. In the duodenum mRNA levels mirrored this trend. TGF-beta1 expression in the lamina propria was absent before d 19, and increased progressively over time. Maternal milk TGF-beta2 levels are high in early milk and decrease during the weaning period. In contrast, endogenous TGF-beta production in the small intestine increases during the weaning period.

Epithelial growth of the small intestine in human infants

BACKGROUND

Findings in studies in rodents have suggested that epithelial growth of the small intestine is dependent on activation of the immune system. The purpose of this study was to compare changes of postnatal epithelial growth with immunologic activity in humans.

METHODS

Duodenal biopsies were obtained by endoscopy from 74 infants. Villus area, crypt length, and mitotic count were measured, using a microdissection technique. Enterocyte height, intraepithelial lymphocytes and mucosal mast cells were recorded in histologic sections, and soluble interleukin-2 receptor levels were measured in sera. These data were compared with those from 77 adult control subjects.

RESULTS

Mean +/- SD villus area was similar in infants compared with that in adults (0.364 +/- 0.108 mm2 vs. 0.339 +/- 0.1 mm2); but mean crypt length was 31% longer (270 +/- 56 microm vs. 206 +/- 29 microm; p < 0.0001), and mitotic count was 68% higher (4.2 +/- 2.8 vs. 2.5 +/- 1 per crypt; p < 0.0001) in infants. Enterocyte height was lower during infancy (27.0 +/- 3.4 microm vs. 30.9 +/- 4.6 microm; p < 0.0001). There was no evidence of a trophic effect on the small intestine of breast feeding compared with the effect of bottle feeding. Counts of intraepithelial lymphocytes but not mucosal mast cells were significantly less in infants. Mean soluble interleukin-2 receptor levels peaked during early infancy, compared with levels in adults (1,820 +/- 596 U/ml vs. 695 +/- 359 U/ml).

CONCLUSION

These results indicate that epithelial proliferation is increased during infancy at an age when immunologic activity is high.

Postnatal changes in mucosal immune response: a physiological perspective of breast feeding and weaning

There are profound changes of immune activity during infancy from suppression during breast feeding, activation with weaning, and later intrinsic down-regulation after weaning. Breast feeding, as well as protecting against infections, seems to have a fundamental role in modifying the immune system against certain disease states. Transforming growth factor (TGF)beta in breast milk may mediate this immunosuppressive effect. Although the infant immune system is not in an adult state, the notion that the infant immune system is immature is difficult to reconcile with evidence that most infants respond appropriately to immunization and to infections. The systemic immune system of neonates may be subject to Th2 immune deviation, while the mucosal immune system, particularly of the gastrointestinal tract and probably the respiratory tract, is up-regulated with physiological inflammation during infancy. Weaning is associated with a peak of intestinal immune activation which includes mucosal mast cells and T cells. The physiological effects of this activation are promotion of epithelial growth of the small intestine and initial activation of mechanisms leading to subsequent down-regulation of the physiological heightened immune activity. This coincides with the development of mucosal (oral) tolerance to food and bacterial antigens.

Analysis of the natural human IgG antibody repertoire: life-long stability of reactivities towards self antigens contrasts with age-dependent diversification of reactivities against bacterial antigens

We used a quantitative immunoblotting technique to analyze the repertoires of IgG antibody reactivities in the serum of healthy young children, young adult males and aged males with self and non-self antigens. Densitometric patterns of reactivity of purified IgG with self antigens were highly conserved between individuals within a given age group and across age groups. Inter-individual differences were observed, however, upon analysis of self reactivities of IgG in whole serum. A striking heterogeneity between individuals within a given age group and across age groups characterized the reactivity of purified IgG and of IgG in whole serum with bacterial antigens. Inter-individual differences were more marked among aged individuals than among individuals of other age groups. Analysis of variances of reactivities of IgG with bacterial antigens further demonstrated an increased diversity of repertoires of aged donors compared with those of young adults and children. Our results document the stability of the self-reactive repertoires of IgG throughout life, which contrasts with the diversification of the repertoire of IgG antibody reactivities directed toward foreign antigens with aging. These findings support the concept that self-reactive antibody repertoires are positively selected throughout life by a restricted set of self antigens shared by all individuals.

Neuropeptide depletion by capsaicin does not prevent mucosal mast cell activation in the rat at weaning

Substance P release by enteric nerves could be an initiating factor for mucosal mast cell (MMC) activation that is associated with weaning in the rat. Capsaicin, which depletes substance P from enteric nerves, should therefore prevent MMC degranulation. Rat pups received either capsaicin (50 mg/kg) or vehicle control subcutaneous injections at 3 and 6 days of life. Capsaicin-treated and control litters were killed at 16, 18, 20, 22, 24 and 26 days of life. MMC activation was measured by serum levels of rat mast cell protease II (RMCPII). Intestinal development was assessed by microdissection to measure villus area, crypt length and crypt cell production rate. RMCPII levels were similar in capsaicin-treated and control rats and peaked at day 22 of life, and intestinal development was not retarded by capsaicin treatment. We conclude that substance P release is unlikely to be an initiating factor for the MMC activation that is associated with weaning.