A comparative study of gut-associated lymphoid tissue in calf and chicken

Selenium Rescues Aflatoxin B1-Inhibited T Cell Subsets and Cytokine Levels in Cecal Tonsil of Chickens

Cecal tonsil is the largest peripheral lymphoid organ of the gut-associated lymphoid tissue executing immune function. To evaluate the protective effect of selenium (Se) on the cecal tonsil of chicken exposed to aflatoxin B₁ (AFB₁), 144 1-day-old healthy Cobb chickens were randomly divided into four groups, and fed with basal diet (control group), 0.6 mg/kg AFB₁ (AFB₁ group), 0.4 mg/kg Se supplement (+Se group), and 0.6 mg/kg AFB₁ + 0.4 mg/kg Se supplement (AFB₁ + Se group) for 21 days, respectively. The results showed that AFB₁ significantly decreased the percentages of CD3⁺, CD3⁺CD4⁺, CD3⁺CD8⁺ T cells, and the CD4⁺/CD8⁺ ratio, and suppressed the expressions of IL-2, IL-4, TNF-α, and IFN-γ mRNA in the cecal tonsil. However, Selenium (Se) supplied in the diets restored the percentages of T cell subsets, the CD4⁺/CD8⁺ ratio, and mRNA expressions of cytokines in the AFB₁ group to be close to those in the control group, and did not exhibit obvious toxicity to the cecal tonsil. These results indicated that Se exerted protective effect against AFB₁ on the functions of cecal tonsil, and also partially uncovered a new role of Se that could protect cecal tonsil of chickens from immunotoxicity of AFB₁.

Effect of dietary fructooligosaccharide supplementation on internal organs Salmonella colonization, immune response, ileal morphology, and ileal immunohistochemistry in laying hens challenged with Salmonella enteritidis

A study was conducted to evaluate the efficacy of fructooligosaccharides (FOS) in controlling the infection of Salmonella Enteritidis (SE) in White Leghorns. A total of 30 laying hens (white leghorns W-36) were challenged both orally and cloacally with approximately 108 colony-forming units of nalidxic acid resistant SE (SENAR) and divided into 3 treatments: 1) SENAR challenged + 0.0% FOS, 2) SENAR challenged + 0.5% FOS (Nutraflora), and 3) SENAR challenged + 1.0% FOS. SENAR recovery via fecal shedding was measured at 3- and 6-d post-infection (dpi), whereas in the ceca and internal organs, SENAR recovery was measured at 7-d post-infection. In the first experiment, there was a 1.0 log10 and a 1.3 log10 reduction in cecal SENAR by supplementation of FOS at 0.5 and 1.0%, respectively. In the second experiment, there was a 0.6 log10 and a 0.8 log10 reduction in cecal SENAR by supplementation of FOS at 0.5 and 1.0%, respectively. Fecal shedding was significantly lower in 1.0% FOS supplemented groups compared to SENAR challenge 0.0% FOS. There was no significant difference among the 3 treatments on SENAR recovery in liver with gall bladder and ovaries. However, the frequency of positive SENAR in the ovaries (10 to 40%) in SENAR challenge 0.0% FOS was significantly lower than liver with gall bladder (60 to 80%) in both experiments. There was a significant upregulation of toll-like receptor-4 in 1.0% FOS and interferon gamma in both 0.5 and 1.0% FOS. Histologic measurements of ileal villi height and crypt depth were similar across all treatments. Immunohistochemistry analyses of ileal samples showed that immunoglobulin A positive cells increased as FOS concentration increased reaching significance at 1.0% as well as altered cytokine gene expression in the ileum. Further, FOS supplementation also reduced cecal SENAR and feces SENAR levels. Collectively, the results suggest that dietary supplementation with FOS may impair SE pathogenesis while modulating humoral immunity within the gut-associated lymphoid tissue.

Effect of dietary bacteriophage supplementation on internal organs, fecal excretion, and ileal immune response in laying hens challenged by Salmonella Enteritidis

With the current researches on replacing antibiotics with different dietary interventions, bacteriophages (BP) are potential antimicrobial intervention because of their ability to affect specific bacteria. A study was conducted to evaluate the role of BP against Salmonella enterica serovar Enteritidis (SE) on SE internal organs colonization and ileum immune response in laying hens. Hens were challenged both orally and intracloacally with 108 cfu/mL cells of nalidixic acid resistant Salmonella Enteritidis (SENAR). Thirty-two Single Comb White Leghorns were randomly allocated to 4 dietary treatments: 1) unchallenged control (negative control; T1), 2) SENAR challenged control (positive control; T2), 3) SENAR challenged + 0.1% BP (T3), and 4) SENAR challenged + 0.2% BP (T4). The number of SENAR in the ceca was significantly reduced by 0.2% BP supplementation (P < 0.05) at 7 d post infection (dpi). The respective number of SENAR was reduced from 2.9 log cfu/gm in T2 and T3 to 2.0 log cfu/gm in T4. There was no significant effect of T3 on reduction of numbers of cecal SENAR. A significant reduction of SENAR was observed in the liver with gall bladder (LGB) from 0.75 in T2 to 0.18 log cfu/gm in T4. In the spleen, T4 significantly reduced (P < 0.05) SENAR to 0.56 log cfu/gm compared to T2 and T3 (0.94 log cfu/gm). There was no significant effect of T3 in reduction of prevalence of spleen SENAR. By supplementing 0.2% BP (T4), the SENAR in the ovary was reduced to 0 log cfu/gm. There was a significant reduction (P < 0.05) in fecal SENAR at 6 dpi by T4 (0.71 log cfu/gm) compared to the positive control (1.57 log cfu/gm). The expression of interferon (IFN)-Γ, interleukin (IL)-6, and IL-10 was significantly increased in the ileum by SENAR challenge compared to the negative control. This study suggests that apart from commonly used prebiotics or probiotics, BP are pathogen-specific and can be used as one of the dietary strategies to reduce SE colonization and induce immune modulation in laying hens.

The Unusual Genetics and Biochemistry of Bovine Immunoglobulins

Antibodies are the key circulating molecules that have evolved to fight infection by the adaptive immune system of vertebrates. Typical antibodies of most species contain six complementarity-determining regions (CDRs), where the third CDR of the heavy chain (CDR H3) has the greatest diversity and often makes the most significant contact with antigen. Generally, the process of V(D)J recombination produces a vast repertoire of antibodies; multiple V, D, and J gene segments recombine with additional junctional diversity at the V-D and D-J joints, and additional combinatorial possibilities occur through heavy- and light-chain pairing. Despite these processes, the overall structure of the resulting antibody is largely conserved, and binding to antigen occurs predominantly through the CDR loops of the immunoglobulin V domains. Bovines have deviated from this general paradigm by having few VH regions and thus little germline combinatorial diversity, but their antibodies contain long CDR H3 regions, with substantial diversity generated through somatic hypermutation. A subset of the repertoire comprises antibodies with ultralong CDR H3s, which can reach over 70 amino acids in length. Structurally, these unusual antibodies form a β-ribbon "stalk" and disulfide-bonded "knob" that protrude far from the antibody surface. These long CDR H3s allow cows to mount a particularly robust immune response when immunized with viral antigens, particularly to broadly neutralizing epitopes on a stabilized HIV gp140 trimer, which has been a challenge for other species. The unusual genetics and structural biology of cows provide for a unique paradigm for creation of immune diversity and could enable generation of antibodies against especially challenging targets and epitopes.

New insight into the origin of IgG-bearing cells in the bursa of Fabricius

The bursa of Fabricius is a primary lymphoid organ for B-cell development and gut-associated lymphoid tissue. After hatching, IgG-containing cells with reticular branches are found in the medulla of bursal follicles on frozen sections stained with anti-Cγ antibody, and IgM(+)IgG(+) B cells are detected in single-cell suspension of the bursa. IgG-containing cells in the medulla do not biosynthesize IgG and are composed of aggregated maternal IgG and environmental antigens. Then, those cells in the medulla are acknowledged as follicular dendritic cells retaining immune complexes. Also, it is presumed that IgM(+)IgG(+) B cells are generated by the attachment of immune complexes to IgM(+) bursal B cells because IgM(+)IgG(+) B cells are induced by antigen-dependent attachment of maternal IgG. Therefore, it is reasonable to suppose that immune complexes exert further B-cell differentiation in the medulla.

C6, a new monoclonal antibody, reacts with the follicle-associated epithelium of calf ileal Peyer's patches

The follicle-associated epithelium (FAE) of Peyer's patches (PPs) contains M cells that are important for reducing mucosal immune responses by transporting antigens into the underlying lymphoid tissue. We generated a monoclonal antibody (C6) that reacted with the FAE of calf ileal PPs, and analyzed the characteristics of C6 using immunohistochemistry and Western blotting. FAE of the ileal PP was stained with C6 during both late fetal developmental and postnatal stages. Neither the villous epithelial cell nor intestinal crypt basal cells were stained at any developmental stage. During the prenatal stages, FAE of the jejunal PP was C6-negative. However, a few C6-positive cells were distributed diffusely in some FAE of the jejunal PPs during the postnatal stages. The protein molecular weight of the antigen recognized by C6 was approximately 45 kDa. These data show that C6 is useful for identifying the FAE in ileal PPs and further suggest that differentiation of the FAE in these areas is independent of external antigens.

Differential cytokine expression in T-cell subsets of chicken caecal tonsils co-cultured with three species of Lactobacillus

Members of the intestinal microbiota play an important role in the development of T-cells. Little is known about responses of intestinal T-cell subsets of chickens to commensal bacteria. Therefore, we set out to characterise cytokine responses in T-cells after exposure to lactobacilli. Caecal tonsil mononuclear cells were isolated and co-cultured with Lactobacillus acidophilus, Lactobacillus reuteri and Lactobacillus salivarius for 12 hours. Subsequently the CD4+ and CD8+ cells were fractionated by flow cytometry and the expression of pro- and anti-inflammatory cytokines as well as Toll-like receptor 21 (TLR21) was determined. The results demonstrated that chicken CD4+ and CD8+ T-cells express TLR21 and that the various isolates of lactobacilli differentially induces the expression of interleukin 10, interferon-gamma and transforming growth factor beta. Our results demonstrate that different Lactobacillus species have the capacity to regulate intestinal T-cell responses and that these responses may be important to intestinal homeostasis.

The origin of IgG-containing cells in the bursa of Fabricius

The bursa of Fabricius of the chicken is known as a primary lymphoid organ for B-cell development. Morphologically, the origin of IgG-containing cells in the bursa has not been clear until now, because abundant maternal IgG (MIgG) is transported to the chick embryo and distributed to the bursal tissue around hatching. Thus, it has been difficult to find out whether these cells themselves biosynthesize IgG or if they acquire MIgG via attachment to their surface. Our present study employing in situ hybridization clarified that IgG-containing cells in the medulla of bursal follicles did not biosynthesize IgG. To study the role of MIgG in the development of those IgG-containing cells, MIgG-free chicks were established from surgically bursectomized hen (SBx-hen). We found that, on the one hand, deprivation of MIgG from chicks completely inhibited the development of IgG-containing cells in the medulla after hatching. On the other hand, administration of MIgG to MIgG-free chicks recovered the emergence of those cells. In addition, we observed that those cells did not bear a B-cell marker and possessed dendrites with aggregated IgG. These results demonstrate that IgG-containing cells in the medulla are reticular cells that capture aggregated MIgG. Moreover, we show that the isolation of the bursa from environmental stimuli by bursal duct ligation (BDL) suppressed the development of IgG-containing cells after hatching. Thus, it is implied that environmental stimulations play a key role in MIgG aggregations and dendritic distributions of aggregated MIgG in the medulla after hatching.

Effects of lactobacilli on cytokine expression by chicken spleen and cecal tonsil cells

Lactobacillus acidophilus, Lactobacillus reuteri, and Lactobacillus salivarius are all normal residents of the chicken gastrointestinal tract. Given the interest in using probiotic bacteria in chicken production and the important role of the microbiota in the development and regulation of the host immune system, the objective of the current study was to examine the differential effects of these bacteria on cytokine gene expression profiles of lymphoid tissue cells. Mononuclear cells isolated from cecal tonsils and spleens of chickens were cocultured with one of the three live bacteria, and gene expression was analyzed via real-time quantitative PCR. All three lactobacilli induced significantly more interleukin 1beta (IL-1beta) expression in spleen cells than in cecal tonsil cells, indicating a more inflammatory response in the spleen than in cecal tonsils. In cecal tonsil cells, substantial differences were found among strains in the capacity to induce IL-12p40, IL-10, IL-18, transforming growth factor beta4 (TGF-beta4), and gamma interferon (IFN-gamma). In conclusion, we demonstrated that L. acidophilus is more effective at inducing T-helper-1 cytokines while L. salivarius induces a more anti-inflammatory response.

Comparative studies on the secondary lymphoid tissue areas in the chicken bursa of Fabricius and calf ileal Peyer's patch

The chicken bursa of Fabricius and calf ileal Peyer's patch are thought to be the primary lymphoid organs of B cell development. In the bursa, the existence of secondary lymphoid tissue, called the diffusely infiltrated area, has been recognized. Recently, we have found the presence of a region of secondary lymphoid tissue in the ileal Peyer's patch at the period of the most rapid growth of this organ. In this study, we compared the development of these secondary lymphoid tissue regions in the bursa and ileal Peyer's patch histologically. Before hatching, lymphatic follicle formation occurred in the bursa, but not in the diffusely infiltrated area, where only a small number of lymphoid cells were found. However, during fetal calf development, lymphatic follicle formation occurred not only in the primary lymphoid organ but also in the secondary lymphoid tissue regions. Therefore, the prenatal development of the secondary lymphoid tissue regions of the bursa and ileal Peyer's patch were distinct. After hatching, formation of the germinal center, which contained many CD4+ cells, was observed in the diffusely infiltrated area of the bursa. After birth, many CD4+ cells and IgG mRNA expression were observed in the lymphatic follicle of the secondary lymphoid tissue regions in the ileal Peyer's patch, but rarely in the ileal Peyer's patch lymphatic follicles. The change of character of these secondary lymphoid tissue regions at the postnatal stage might be dependent on external antigens.

Interactions between commensal bacteria and the gut-associated immune system of the chicken

The chicken gut-associated lymphoid tissue is made up of a number of tissues and cells that are responsible for generating mucosal immune responses and maintaining intestinal homeostasis. The normal chicken microbiota also contributes to this via the ability to activate both innate defense mechanisms and adaptive immune responses. If left uncontrolled, immune activation in response to the normal microbiota would pose a risk of excessive inflammation and intestinal damage. Therefore, it is important that immune responses to the normal microbiota be under strict regulatory control. Through studies of mammals, it has been established that the mucosal immune system has specialized regulatory and anti-inflammatory mechanisms for eliminating or tolerating the normal microbiota. The mechanisms that exist in the chicken to control host responses to the normal microbiota, although assumed to be similar to that of mammals, have not yet been fully described. This review summarizes what is currently known about the host response to the intestinal microbiota, particularly in the chicken.

Characteristic cellular composition of germinal centers

We established the method of isolating individually encapsulated germinal centers (GCs) from immunized spleen and analyzed single cell suspension of GCs by flowcytometry. In GCs, the high frequency of sIgG+ cells (29%) and sIgA+ cells (5%) was detected. Two-color flowcytometry analysis showed that GCs contained 27% of sIgM-IgG+ cells, in which isotype switch from IgM to IgG had occurred, and 5% of Bu1-IgG+ cells, which were differentiating into plasma cells. On the other hand, sIgM-IgG+ and Bu1-IgG+ cells were not detected in the bursa, which contained 95% of B cells and only 1% of T cells. CD4+ but not CD8+ T cells were detected in the light zone of GCs and these CD4+ T cells are supposed to play a key role in isotype switching and differentiation into plasma cells in GCs. These results clearly demonstrate that GCs provide a site for isotype switching and differentiation into plasma cells.

Histological studies on the ontogeny of bovine palatine and pharyngeal tonsil: germinal center formation, IgG, and IgA mRNA expression

The development and distribution of lymphocyte subsets in calf palatine and pharyngeal tonsil were examined. During prenatal development, B cells were distributed in the subepithelial area, and T cells and MHC class II(+) cells were found in the deep layer of B-cell area, respectively, in both tonsils. At neonatal stage, lymphoid follicle containing a few CD4(+) cells have been formed in both tonsils. IgG(+) and IgA(+) cells were found in the parafollicular and epithelial area. At 3 months old, many germinal centers were recognized in both tonsils. CD4(+) cells and IgG mRNA expression were detected in light zone of germinal centers. Many IgG, and IgA mRNA expressions also could be detected in the parafollicular and subepithelial area of both tonsils. The data suggest that both tonsils have an important role of local immune defense against invading antigen after birth. The comparison of the histological characteristics of tonsil and Peyer's patch during ontogeny is also discussed.

The postnatal development of the mucosal immune system and mucosal tolerance in domestic animals

The mucosal immune system is exposed to a range of antigens associated with pathogens, to which it must mount active immune responses. However, it is also exposed to a large number of harmless antigens associated with food and with commensal microbial flora, to which expression of active, inflammatory immune responses to these antigens is undesirable. The mucosal immune system must contain machinery capable of evaluating the antigens to which it is exposed and mounting appropriate effector or regulatory responses. Since the immune system is likely to have evolved initially in mucosal tissues, the requirement to prevent damaging allergic responses must be at least as old as the adaptive immune system, and studies of the mechanisms should include a range of non-mammalian species. Despite the importance for rational design of vaccines and for control of allergic reactions, the mechanisms involved are still largely unclear. It is not clear that the classical experimental protocol of "oral tolerance" is, in fact, measuring a biologically important phenomenon, nor is it clear whether tolerance is regulated in the evolutionarily recent organised lymphoid tissue (the lymph nodes) or the more ancient, diffuse architecture in the intestine. The capacity of the immune system to discriminate between "dangerous" and "harmless" antigens appears to develop with age and exposure to microbial flora. Thus, the ability of an individual or a group of animals to correctly regulate mucosal immune responses will depend on age, genetics and on their microbial environment and history. Attempts to manipulate the mucosal immune system towards active immune responses by oral vaccines, or towards oral tolerance, are likely to be confounded by environmentally-induced variability between individuals and between groups of animals.

The sheep and cattle Peyer's patch as a site of B-cell development

In sheep and cattle, the ileal Peyer's patch (PP), which extends one-two meters along the terminal small intestine, is a primary lymphoid organ of B-cell development. B-cell diversity in the ileal PP is thought to develop by combinatorial mechanisms, gene conversion and/or point mutation. These species also have jejunal PP that function more like secondary lymphoid tissues concerned with mucosal immune reactions. These two types of PP differ significantly in their histology, ontogeny and the extent of lymphocyte traffic. The prenatal development of follicles in the PP begins first in the jejunum during the middle of gestation and then in the ileum during late gestation. B-cells proliferate rapidly in the ileal PP follicle; up to five percent of these cells survive while the majority dies by apoptosis, perhaps driven by the influence of environmental antigen and/or self-antigen. The surviving cells migrate from the ileal PP and populate the peripheral B-cell compartment. By adolescence, the ileal PP has involuted but the function of jejunal PP, compatible with a role as secondary lymphoid organ, continues throughout life. In this review, we focus on the development of PP as a site of B-cell repertoire generation, positive and negative B-cell selection, and the differences between ileal PP and jejunal PP.

In ovo vitelline duct ligation results in transient changes of bursal microenvironments

The avian bursa of Fabricius has a direct connection to the cloaca via the bursal duct. Using the bursal duct ligation technique, it has been clearly shown that the B cells of the bursal follicles develop under the influence of cloacal antigens. These antigens have been suggested to be present on the bursal secretory dendritic cells in immunoglobulin G (IgG)-containing complexes. We studied the effect of maternal (yolk) antigens on the early development of B cells and the appearance of IgG-containing complexes of the bursal dendritic cells with a novel embryo manipulation technique, in ovo vitelline duct ligation. This operation blocked the direct (intestinal) transport of yolk substances into the intestine, but left the vitelline circulation intact. Vitelline duct ligation performed on embryonic day 17 resulted in serious but transient bursal underdevelopment during the first week of life: (1) IgG and the follicular dendritic cell marker 74.3 were not detectable on the bursal secretory dendritic cells, in spite of a normal serum IgG level and free communication with the cloacal lumen; (2) the number of B cells in the follicles was greatly reduced and they showed an altered phenotype, resembling that of the prebursal B cells. The intracloacal administration of different proteins effectively restored the bursal phenotype. These data suggest that maternal antigens indirectly help the maturation of bursal secretory dendritic cells and concomitantly that of B cells during the first week of life.

Impaired immune responses in broiler hatchling hindgut following delayed access to feed

One of the key stimulators of intestinal development in the chick is physical exposure to feed, while feed withholding delays the onset of gut development. A delay of 24-72 h in onset of feeding is quite common in the poultry industry due to variation in hatching time and hatchery treatments. As intestinal development occurs in concert with the development of the gut associated lymphoid tissue (GALT), we investigated the effects of short term feed withholding on development of GALT in broiler hatchlings. GALT activity was determined by antibody production (systemic and locally in the gut), distribution of B and T lymphocytes in the gut, expression of lymphocyte specific genes, and distribution of B and T lymphocytes in the cloacal bursa. Our findings show that while development of GALT in the foregut (duodenum, jejunum, ileum) was only slightly and temporarily impeded by feed withholding, GALT activity in the hindgut and the gut-related cloacal bursa was significantly delayed during the first 2 weeks of life: Systemic and intestinal antibody responses following rectal immunization to antigen were lower, colonization of the hindgut (cecum and colon) by T and B lymphocytes was delayed, as well as the expression of chIL-2 mRNA in hindgut T lymphocytes. We also found that the increase of B and T population size in the cloacal bursa was delayed with time. Full recovery occurred from 2 weeks of age. The 2-week vulnerable period should be seriously considered in circumstances where hatchlings are in transit for extended periods from hatcheries to farms.

Kinetics and distribution of bovine gammadelta T-lymphocyte in the intestine: gammadelta T cells accumulate in the dome region of Peyer's patch during prenatal development

The kinetics and distribution of gammadelta T cells in bovine intestine including jejunal and ileal Peyer's patch were examined. The number of gammadelta T cells increased significantly in the dome region during prenatal development, but decreased notably after birth. The number of some gammadelta T cells, CD4+ cells, and CD8+ cells in the intestinal villi remained constant during prenatal development, but increased significantly after birth. The kinetics of the gammadelta T cells in the dome region during prenatal development were quite distinct from those of the gammadelta T cells, CD4+ cells, and CD8+ cells in the intestinal villi. In the fetal ileum at full-term gestation, the frequencies of expression of the T-cell receptor gamma variable region (TCR Vgamma) family were TCR Vgamma1 (48%), Vgamma2 (4%), and Vgamma5 (48%). However, in 2-month-old calf ileum, TCR Vgamma5 (90%) was dominant. We speculate that functional differences exist between gammadelta T cells in the dome region during prenatal development and in the intestinal villi after birth.

Development of Ileal Peyer's Patches and Follicle Associated Epithelium in Bovine Foetuses

The development of the ileal Peyer's patches (ilPP) and follicle associated epithelium (FAE) was examined in 30 bovine foetuses ranging from 73 to 271 days of gestation by light and transmission electron microscopic methods. The first primordial ilPP was encountered in the foetus at 164 days of gestation The ilPP were found to have been formed from the aggregation of lymph follicles in the foetus at 227 days of gestation whereas in the foetus at 271 days of gestation the follicular development was observed to have been completed. While the cells in the FAE in the foetus at 164 days of gestation and those older were cuboidal, those of the foetus at 271 days of gestation were columnar. As from the foetus at 227 days of gestation, however, the FAE was found to be composed of uniform lymphoepithelial cells with an increase in the number of intraepithelial leukocytes. In the early stages, whereas the apical surfaces of the FAE cells appeared shorter with microfolds, with advancing age the apical surfaces of the FAE cells were observed to be heterogeneous. Our results suggest that bovine ilPP and FAE cells are histologically and functionally mature before birth.

Histological studies on the ontogeny of bovine gut-associated lymphoid tissue: appearance of T cells and development of IgG+ and IgA+ cells in lymphoid follicles

The development and distribution of lymphocyte subsets in bovine gut-associated lymphoid tissues (ileal and jejunal Peyer's patches (PP)) were examined. Before birth, the composition of lymphocyte subsets in both PP follicles did not differ except for the dimensions of the interfollicular area and the dome region. Many IgM+ cells were observed in these follicles, but very few CD3+, IgG+, and IgA+ cells could be found. At neonatal period, the IgG+ cells, which did not produce IgG mRNA, were dominant within both PP follicles. From 1 month after birth, many CD3+ cells, IgG mRNA expression, and IgA mRNA expression were detected within the jejunal PP follicles, but very few were in the ileal PP follicles. These data suggest that the characteristics of the jejunal PP follicles metamorphose into secondary lymphoid tissue such as germinal centers at around 1 month after birth, whereas the characteristics of ileal PP follicles were distinct from those of germinal centers.

Cell Proliferation, Apoptosis, and B- and T-Lymphocytes in Peyer's Patches of the Ileum, in Thymus and in Lymph nodes of Preterm Calves, and in Full-Term Calves at Birth and on Day 5 of Life

Peyer's patches, thymus, and lymph nodes contain the majority of lymphocytes. We have studied proliferation rates, apoptosis rates, and numbers of B- and T-lymphocytes in Peyer's patches in ileum, thymus, and mesenterial and prescapular lymph nodes (LM and LP) in unfed preterm calves (GrP; born 13 d before expected normal term after dams were injected with prostaglandin F2alpha and glucocorticoids) and normal-term calves (GrF) immediately after birth and on d 5 of life after feeding colostrum for 4 d (GrC). Immunohistochemical methods in conjunction with incorporation of 5-bromo-2'-deoxyuridine or terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling were used to evaluate cell proliferation rates and apoptosis rates, respectively. The number of T- and B-lymphocytes was determined with monoclonal antibodies directed against CD3 and CD79, respectively. In GrF compared with GrP, there were higher numbers of proliferating and apoptotic cells in LM and LP, of B-lymphocytes in paracortex and follicles of LM and LP, and of proliferating cells in cortex and medulla of thymus. In thymus cortex and medulla, numbers of proliferating cells were higher in GrC than in GrF. Apoptotic rates were generally smaller at all sites of Peyer's patches in GrC than in GrF, and proliferation rates increased from GrP to GrF in intrafollicular areas and from GrF to GrC in all tissues. Numbers of T-lymphocytes in Peyer's patches were higher in GrF than in GrP, but lower in GrC than in GrF, except in the domes. Numbers of B-lymphocytes did not change in Peyer's patches despite high proliferation and low apoptotic rates, suggesting that they leave Peyer's patches during the first days of life. In conclusion, proliferation and apoptosis rates and numbers of B- and T- lymphocytes in Peyer's patches in ileum, thymus, and LM and LP exhibited different developmental changes and were affected by feeding.

Effects of dexamethasone on lymphoid tissue in the gut and thymus of neonatal calves fed with colostrum or milk replacer

An increased susceptibility to disease in neonatal calves may be attributable to high glucocorticoid levels that influence immune reactions. We tested whether dexamethasone (DEXA) administration influences the proliferation, apoptosis, and number of B- and T-lymphocytes in Peyer's patches (PP) and thymus in calves fed colostrum (C) or a milk-derived formula. All calves were subcutaneously administered bovine colostrum-derived immunoglobulin G and fed chicken-egg derived immunoglobulins that protected against rotavirus and pathogenic Escherichia coli. The DEXA (30 microg/kg of BW daily) was injected for 4 d into groups fed colostrum on the first 3 d (CD+) and those fed the formula that contained nutrients in amounts as in colostrum but no immunoglubulin G (FD+). Groups CD- and FD were fed the same as the other two groups, but did not receive DEXA. Immunohistochemical methods were used to evaluate cell proliferation rates (by labeling of 5-bromo-2'-deoxyuridine), apoptosis rates (by terminal deoxynucleotidyl transferase-mediated X-dUTP nick end labeling). Numbers of T- and B-lymphocytes were determined with antibodies specific for CD3 and CD79 surface proteins. There were significant effects (P < 0.05) of DEXA treatment (decrease of cell proliferation rates in follicles of PP and thymus, increase of apoptotic rate in follicles of PP and thymus, decrease of B-lymphocyte numbers in follicles of PP, increase of B-lymphocyte numbers in domes of PP, increase of T-lymphocyte numbers in follicles of PP, and a decrease of intraepithelial T-lymphocyte numbers). There were significant effects (P < 0.05) of C feeding (decrease of cell proliferation rates in follicles of PP and of B-lymphocyte numbers in interfollicular areas, domes, and follicular-associated epithelium of PP, and an increase of cell proliferation rate in the thymus). A DEXA x feeding interaction (P < 0.001) was found for cell proliferation rate in the thymus. In conclusion, DEXA treatment decreased cell proliferation rates in follicles of PP and thymus and enhanced apoptotic rates in follicles of PP. Colostrum feeding decreased cell proliferation rates, likely of B-lymphocytes, in follicles of PP and numbers of B-lymphocytes in domes, follicular-associated epithelium, and interfollicular areas of PP and enhanced cell proliferation rates and selectively modified DEXA effects in the thymus.

Esophageal tonsil: a novel gut-associated lymphoid organ

The esophageal tonsil of the chicken is a novel, significant element of the gut-associated lymphoid tissue (GALT). Its stable location and histological organization fulfills the meaning of the term "tonsil." The six-to-eight-isolated tonsillar units are located at the border of the esophagus and the proventriculus. The number of tonsillar units is identical with that of the esophageal folds. Each tonsillar unit consists of a crypt lined by lymphoepithelium and surrounded by dense lymphoid tissue, which is organized into T- and B-dependent regions, like peripheral lymphoid organs. The excretory ducts of the mucosal glands of the esophagus are frequently involved in the formation of the lymphoepithelium. The esophageal tonsil is anatomically located cranial to the stomach, unlike the other parts of the GALT. Therefore, it is continuously exposed to undigested environmental antigens, allergens, food, and infectious agents. To develop effective oral vaccines, the existence of the esophageal tonsil has to be taken into account.

Effect of environmental antigens on the Ig diversification and the selection of productive V-J joints in the bursa

In chickens, a single set of unique functional segments of both Ig H and L chain genes is rearranged during early embryogenesis to generate a pool of B cell progenitors that will be diversified in the bursa by gene conversion, forming the preimmune repertoire. After hatching, bursal cells are exposed to environmental Ags in the bursal lumen. We prepared B cells from each single bursal follicle and used PCR-directed Ig L chain gene analysis to study the differentiation of B cells and the effect of antigenic stimulation from the bursal lumen on the neonatal chicken B cell repertoire formation. Selective amplification of B cell clones with a productive V-J joint was observed during the late embryonic stage, possibly by the interaction with ligands expressed on the bursal stroma and further accelerated in the neonatal chicken. Administration of the artificial Ags into the bursal lumen before the isolation of bursa by bursal duct ligation in the embryo caused a significant increase in lymphocytes with a productive V-J joint in the neonatal chicken bursa compared with the isolated bursa. Intra- and interclonal diversity of a complementarity-determining region measured by an evolutionary distance increased during bursal development. Clonal diversification did not require stimulation by artificial Ags from the bursal lumen. Thus, the preimmune repertoire in the bursa is generated by gene conversion during Ag-independent B cell proliferation, and antigenic stimulation from the bursal epithelium to bursal B cells plays roles in the selection of clones with a productive V-J joint.