Esbjörn Telemo

Impaired regulatory T cell function in germ-free mice

Regulatory T cells (Treg) are crucial for the maintenance of tolerance to auto‐antigens and harmless exogenous antigens. Here, we studied the role of the commensal microbiota for the development and function of Treg. CD4+CD25+ T cells were obtained from peripheral lymph nodes (PLN) and mesenteric lymph nodes (MLN) of germ‐free (GF) and conventional (conv) NMRI mice and tested for phenotype and functional suppressive capacity. CD4+CD25+ T cells from GF mice showed a lower relative gene expression of fork head box p3 gene (Foxp3) and were not as potent suppressors in vitro as CD4+CD25+ T cells from conv animals. Intracellular staining for Foxp3 and CTLA‐4 revealed proportional and regional differences in putative Treg subsets between conv and GF mice. Fewer of the CD4+CD25+ T cells in GF MLN expressed Foxp3 and CTLA‐4, while the expression of these markers was similar amongst the CD4+CD25+ T cells in PLN of conv and GF mice. The largest difference between conv and GF Treg was observed in the liver draining celiac lymph node, where GF mice had fewer putative Treg as compared to conv mice. We propose that the presence of a microbial flora favors the development of a fully functional Treg population.

The Transfer of Immunity from Mother to Child

Abstract: The newborns immune system grows fast from a small size at birth by exposure primarily to the intestinal microflora normally obtained from the mother at and after birth. While building up its immune system, the infant is supported by the transplacental IgG antibodies, which also contain anti‐idiotypic antibodies, possibly also actively priming the offspring. The second mode of transfer of immunity occurs via the milk. Numerous major protective components, including secretory IgA (SIgA) antibodies and lactoferrin, are present.

Immunomodulatory effects of Lactobacillus plantarum colonizing the intestine of gnotobiotic rats

We have studied the effect of the probiotic strain Lactobacillus plantarum 299v on the immune functions of gnotobiotic rats. One group of germ‐free rats was colonized with the type 1‐fimbriated Escherichia coli O6:K13:H1 and another group with the same E. coli strain together with L. plantarum 299v. One and 5 weeks after colonization, bacterial numbers were determined in the contents of the small intestine, caecum and mesenteric lymph nodes. Small intestinal sections were examined for CD8+, CD4+, CD25+ (IL‐2R α‐chain), IgA+ and MHC class II+ cells and mitogen‐induced spleen cell proliferation was determined. Immunoglobulin levels and E. coli‐specific antibodies were measured in serum. Rats given L. plantarum in addition to E. coli showed lower counts of E. coli in the small intestine and caecum 1 week after colonization compared with the group colonized with E. coli alone, but similar levels after 5 weeks. Rats colonized with L. plantarum+ E. coli had significantly higher total serum IgA levels and marginally higher IgM and IgA antibody levels against E. coli than those colonized with E. coli alone. They also showed a significantly increased density of CD25+ cells in the lamina propria and displayed a decreased proliferative spleen cell response after stimulation with concanavalin A or E. coli 1 week after colonization. The results indicate that L. plantarum colonization competes with E. coli for intestinal colonization and can influence intestinal and systemic immunity.

Breast‐feeding, a complex support system for the offspring

The newborn has an immune system, very limited in size at birth and its postnatal expansion and maturation takes time. In the meantime the transplacental IgG antibodies from the mother play an important role for the protection of the infant. However, these antibodies act in tissues and induce inflammation and are energy‐consuming. In contrast, the milk secretory IgA antibodies stop microbes already on the mucosa preventing infection, tissue engagement and energy loss. In addition, the milk contains many protective factors such as lactoferrin and oligosacharides functioning as analogues for microbial receptors preventing mucosal attachment, the initial step of most infections. As a result, breast‐feeding significantly reduces the risk of neonatal septicemia, respiratory tract infections, otitis media, diarrhea, urinary tract infections, infection‐induced wheezing and necrotizing enterocolitis. Via several mechanisms it seems that human milk can actively stimulate the immune system of the breast‐fed infant. This reduces the risk of infections like otitis media, respiratory tract infections, diarrhea and infection‐induced wheezing for several years after the termination of breast‐feeding. Furthermore, it seems that breast‐feeding decreases the risk of attracting celiac disease and allergic diseases. The latter has been much debated, but a recent critical review of published reports gives good support for long‐term protection of allergic diseases, especially in high‐risk children.

Galectin-3 functions as an opsonin and enhances the macrophage clearance of apoptotic neutrophils.

Galectin-3, a beta-galactoside binding, endogenous lectin, takes part in various inflammatory events and is produced in substantial amounts at inflammatory foci. We investigated whether extracellular galectin-3 could participate in the phagocytic clearance of apoptotic neutrophils by macrophages, a process of crucial importance for termination of acute inflammation. Using human leukocytes, we show that exogenously added galectin-3 increased the uptake of apoptotic neutrophils by monocyte-derived macrophages (MDM). Both the proportion of MDM that engulfed apoptotic prey and the number of apoptotic neutrophils that each MDM engulfed were enhanced in the presence of galectin-3. The effect was lactose-inhibitable and required galectin-3 affinity for N-acetyllactosamine, a saccharide typically found on cell surface glycoproteins, since a mutant lacking this activity was without effect. The enhanced uptake relied on the presence of galectin-3 during the cellular interaction and was paralleled by lectin binding to apoptotic cells as well as MDM in a lactose-dependent manner. These findings suggest that galectin-3 functions as a bridging molecule between phagocyte and apoptotic prey, acting as an opsonin. The process of clearance, whereby apoptotic neutrophils are removed by macrophages, is crucial for the resolution of acute inflammation and our data imply that the increased levels of galectin-3 often found at inflammatory sites could potently affect this process.

Breast-feeding, infant formulas, and the immune system

OBJECTIVE Breast-feeding provides many advantages to the offspring, but presently there is an ongoing debate whether or not it prevents allergy any better than certain formulas. This report reviews the mechanisms involved and discusses how breast-feeding may protect against allergy. DATA SOURCES The review builds on an internet-based literature search in addition to our own data. RESULTS Human milk is the food best adapted to the needs of the offspring, also because it provides efficient protection against infections and actively stimulates the development of the infants own immune system. The major host defense system is provided via the secretory IgA antibodies produced in the mammary glands by lymphocytes, which have migrated there from the mothers gut mucosa. Therefore, these antibodies in the milk are primarily directed against the microbes in the mothers gut and her food proteins. As a result, breast-feeding starting directly after delivery will provide an excellent defense against the microbes normally meeting the neonate and needed to induce development of its immune system. The milk also contains numerous components, which seem to enhance the infants host defense as well as capacity to develop tolerance, helping to avoiding allergic reactivity to foods, etc. CONCLUSIONS Several studies show that breast-feeding prevents allergic diseases, but there are also good disagreeing studies. Supported by animal data, it seems that protection is enhanced in areas with more advantageous fat intake, inter alia lower ratio of n-6/n-3 fatty acids. Breast-feeding seems to protect against future development of allergic diseases, but possibly less so in countries with an untoward maternal fat intake.

Serum-derived exosomes from antigen-fed mice prevent allergic sensitization in a model of allergic asthma

Oral tolerance is an active process that starts with sampling of luminal antigens by the intestinal epithelial cells (IEC), followed by processing and assembly with major histocompatibility complex class II and subsequently a release of tolerogenic exosomes (tolerosomes) from the IEC. We have previously shown that tolerosomes can be isolated from serum shortly after an antigen feed, and will potently transfer antigen‐specific tolerance to naive recipients. Here we study the capacity of the tolerosomes to protect against allergic sensitization in a mouse model of allergic asthma. Serum or isolated serum exosomes from tolerized BALB/c donor mice were transferred to syngeneic recipients followed by sensitization and intranasal exposure to ovalbumin (OVA). Blood, bronchoalveolar lavage (BAL) and lymph nodes were sampled 24 hr after the final exposure. The number of eosinophils was counted in BAL fluid and the levels of immunoglobulin E (IgE) and OVA‐specific IgE were measured in serum. Mediastinal and coeliac lymph nodes were analysed by flow cytometry. The animals receiving serum from OVA‐fed mice displayed significantly lower numbers of airway eosinophils and lower serum levels of total IgE as well as of OVA‐specific IgE compared with controls. Moreover, the tolerant animals showed a significantly higher frequency of activated T cells with a regulatory phenotype in both mediastinal and coeliac lymph nodes. The results show that serum or isolated serum exosomes obtained from OVA‐fed mice and administered intraperitoneally to naive recipient mice abrogated allergic sensitization in the recipients.

Tolerosome-induced oral tolerance is MHC dependent

Oral administration of a protein antigen generates a serum factor that induces tolerance when transferred into naïve recipients. This serum factor has been described in rats as consisting of exosome‐like structures or tolerosomes, which express major histocompatibility complex class II molecules (MHCII) and mediate antigen‐specific tolerance. In this study, we investigated the functions of serum‐derived tolerosomes both in vivo and in vitro. Tolerosomes were purified from the 100 000 g pellet fraction of serum from ovalbumin (OVA)‐fed mice. When transferred into naïve recipient mice, the tolerosomes mediated OVA‐specific tolerance. We also found that tolerosomes from OVA‐fed mice induced the activation of OVA‐specific T cells both in vivo and in vitro. The inoculation of severe combined immunodeficiency (SCID) mice with an interferon‐γ‐producing cell line normalized the expression of MHCII in the intestinal epithelial cells and restored their ability to generate tolerosomes. Syngeneic but not allogeneic transfer of tolerosomes from OVA‐fed donors induced tolerance in the recipients. Our results show that tolerosomes can be isolated from mouse serum, that tolerosome‐induced oral tolerance requires MHCII expression in intestinal epithelial cells, and that tolerosomes are functional only in syngeneic recipients.

Antibodies in milk.

The immaturity of the infants immune system and the rapid evolution of pathogens has created a demand for the mother to provide ready made specific defence factors to her offspring. This is achieved during the fetal period by transplacental transport of IgG antibodies, and after birth via IgA antibodies in the breast milk. The breast milk also contains a variety of nonspecific defence factors contributing to its antimicrobial effect. Breast feeding has been shown to decrease morbidity in gastroenteritis, septicemia, otitis media, urinary tract infection, encephalitis, pneumonia, and necrotizing enterocolitis. The antibody content in the mothers milk probably contributes not only to the immediate but also to the long term protection of the infant including both resistance to infection and development of immunological tolerance to harmless environmental antigens.

The immunological role of breast feeding

Hanson LÅ, Silfverdal S-A, Strömbäck L, Erling V, Zaman S, Olcén P, Telemo E. The immunological role of breast feeding. Pediatr Allergy Immunol 2001: 12(suppl 14): 15–19. # Munksgaard 2001. L. Å. Hanson, S.-A. Silfverdal, L. Strömbäck, V. Erling, S. Zaman, P. Olcén, E. Telemo Department of Clinical Immunology, Göteborg University, Göteborg, Sweden, Departments of Paediatrics, Microbiology and Immunology, Örebro Medical Centre Hospital, Örebro, Sweden and Department of Social and Preventive Pediatrics, King Edward Medical College, Lahore, Pakistan