Aharon Friedman

Establishment of immune competence in the avian GALT during the immediate post-hatch period.

Population dynamics of intestinal lymphocytes and the temporal development of lymphocyte functions were studied in broiler chicks during the first 2 weeks post-hatch. This period is of major immunological importance as the chick is immediately exposed to environmental antigens and pathogens. We show that the gut-associated lymphoid tissue contains functionally immature T and B lymphocytes at hatch, and that function is attained during the first 2 weeks of life as demonstrated by mRNA expression of both ChIL-2 and ChIFNgamma. Functional maturation occurred in two stages: the first-during the first week post-hatch, and the second during the second week, which was also accompanied by an increase in lymphocyte population, as determined by expression of antigen receptor genes. Evidence is presented to show that in the intestinal milieu cellular immune responses mature earlier, and are a prerequisite for humoral responses. Hence, the lack of antibody response in young chicks is primarily due to immaturity of T lymphocytes.

Role of Tumor Necrosis Factor α and Its Type I Receptor in Luteal Regression: Induction of Programmed Cell Death in Bovine Corpus Luteum-Derived Endothelial Cells

Abstract The role of tumor necrosis factor α (TNFα) and its type I receptor (TNFRI) in structural luteolysis was investigated. A semiquatitative reverse-transcription polymerase chain reaction (RT-PCR) was used to characterize the pattern of TNFRI mRNA expression within the corpus luteum (CL) throughout the estrous cycle and its cellular distribution. Increase in TNFRI mRNA levels was recorded both in regressed luteal tissue and in CL of cows injected with prostaglandin F2α. All three major cell types composing the CL, steroidogenic (large and small) and endothelial cells expressed the TNFRI gene. A densitometric analysis of TNFRI mRNA expression revealed that resident endothelial cells had significantly higher levels of TNFRI mRNA than steroidogenic luteal cells. The physiological effects associated with TNFRI expression were investigated in the various luteal cell types. TNFα-induced programmed cell death (PCD) in dose- and time-dependent manners of cultured luteal endothelial cells (LECs) but not of in vitro luteinized steroidogenic cells. Several lines of evidence are provided to show that progesterone regulates luteal cell survival: 1) CL and LECs express progesterone receptor mRNA, 2) physiological levels of the steroid abolished TNFα-induced PCD of LECs, and 3) progesterone-producing cells are protected from PCD. In conclusion, this study suggests that TNFα-induced PCD during structural luteolysis is mediated by TNFRI, primarily affects endothelial cells, and that the decline in progesterone, preceding structural luteolysis, is a prerequisite for the initiation of apoptosis in endothelial cells.

Ontogeny of gut associated immune competence in the chick

To accommodate the rapid transition to external nutrients, the chicks gastrointestinal tract undergoes dramatic changes within the first few days of life. These include a rapid increase in mass, villi number and length, enterocyte number, crypt depth and proliferating cells. Concomitant with the development of digestive structures and functions a rapid development of the gut associated lymphoid tissue (GALT) occurs. This lymphoid system works within and in concert with digestive tract parenchyma, however, there is little information describing the normal development and immunological function of the avian GALT in the immediate post-hatch period. The purpose of this review is to summarize current knowledge on the structure and function of the avian GALT during the early post-hatch period. At hatch, the gut is poorly populated by both innate immune leukocytes and lymphocytes. The basal numbers of lymphocytes are the result of early waves migrating from the thymus and bursa of Fabricius. Further waves of lymphocyte migration occur after 4 days of life and continue intermittently with time. In concert with this pattern of lymphocyte population adaptive immunity develops. Hence, the gut of the hatchling is unprotected by adaptive immunity during the first few days of life. Protection during this critical period might be the result of maternal antibody activity or that of the innate immune system. This system appears to be functional at this time, though much work is needed to establish this possibility. Upon maturity of the immune system, most of the immunological activity within the chick GALT is concentrated in the hindgut, and specifically so in the caeca and bursa of Fabricius. Once immune responses have become established the relevant cells disseminate systemically and to other areas of the small intestines. Finally, observations on the beneficial effects of early feeding on development of gut and GALT are discussed with reference to management of hatchlings.

Oral Tolerance: A Biologically Relevant Pathway to Generate Peripheral Tolerance against External and Self Antigens

OT is a relevant biological pathway for generating peripheral tolerance against both self and external antigens with minimal side effects (fig. 3). This route might, therefore, contain promising potential for the treatment of autoimmune and allergic diseases in the human (fig. 3). Thus, oral administration of autoantigens suppresses experimental autoimmune diseases (EAE, EAU, AA, collagen-induced arthritis, NOD diabetes) in a disease- and antigen-specific manner, and oral administration of alloantigens has led to increase of allograft survival. OT might be important in treatment of immune complex diseases and food allergies. OT is mediated by T lymphocytes using at least two nonmutually exclusive mechanisms: suppression and anergy. Suppression can be adoptively transferred by CD8+ T lymphocytes which act by releasing TGF-beta and IL-4 following antigen-specific triggering. Antigen-driven tissue-directed suppression occurs following oral administration of an antigen from the target organ, even if it is not the disease-inducing antigen (bystander suppression). Thus, synthetic peptides can induce OT, and tolerogenic epitopes of antigen may be different from the autoreactive epitope. Due to the promising results in animal models, OT is being tested in clinical trials in multiple sclerosis, rheumatoid arthritis and uveitis [193, 194].

Vaccination against experimental autoimmune encephalomyelitis using a subencephalitogenic dose of autoimmune effector T cells. (2) Induction of a protective anti-idiotypic response

We previously reported that a subencephalitogenic dose (10(4) of activated anti-BP Z1a T cells rendered Lewis rats significantly resistant to EAE induced either actively or adoptively. This resistance was specific to EAE and persisted for over 4 months. The experiments reported in this paper were done to investigate the mechanisms of this resistance. We found that the state of vaccination was marked by a decrease in the in vitro proliferation and in vivo DTH responses to BP. Resistance could be transferred to recipient rats with the thymus or spleen cells of donor vaccinated rats. Vaccination led to the appearance of proliferative and DTH responses that were specifically directed to the Z1a T cells. The kinetics and compartmentalization of this anti-idiotypic responsiveness was studied by vaccinating rats in the hind footpads and monitoring the proliferative reactivity of the draining popliteal lymph node (PLN) and distal cervical lymph node (CLN) cells at various times. We found that the anti-idiotypic reactivity was confined to the PLN on days 5-6 and thereafter became systemic. Excision of the PLN on day 6, but not on days 3 or 11, robbed the rats of their acquired resistance to EAE. In contrast, the PLN cells of the vaccinated rats transferred resistance to naive donors. Thus, the lymphoid population containing cell-mediated anti-idiotypic responsiveness served as a vehicle of resistance. These results suggest that anti-idiotypic T-cell immunity to autoimmune effector T cells is involved in the resistance to EAE induced by T-cell vaccination.

Sex-related differences in immune response and survival rate of broiler chickens

In a comparison between male and female broiler chicks, the mortality rate of males was found to be significantly higher than that of females, starting from the second week of age until marketing at 7 or 8 weeks of age. The main causes of death during this period were various infectious diseases. This observation was explained by differences in the activity of humoral and cell-mediated immune responses between the sexes. In tests of antibody responses of young chicks to a variety of antigens (bacterial-E. coli, viral-Newcastle disease virus, and protein antigen-bovine serum albumin), females responded 24-72 h earlier than males and with higher peak antibody titers. In-vitro proliferation of T-lymphocytes to purified protein derivative and E. coli showed an earlier and greater response in females. The correlation between immune responsiveness and survival, as tested by challenging vaccinated chicks with pathogenic E. coli, showed a significantly higher mortality rate in vaccinated males, that was correlated with their lower antibody titer. We concluded, therefore, that sex-related differences in mortality rates of broiler chicks may result from a less efficient immune response in males.

Immune responses of chickens to dietary protein antigens. I. Induction of systemic and intestinal immune responses following oral administration of soluble proteins in the absence of adjuvant.

Oral administration of protein antigens in solution leads to the development of oral tolerance in most mammals but rarely so in the chicken. As dietary proteins are not expected to be immunogenic, the present study was undertaken to evaluate immunological consequences following oral exposure to protein antigens in chicks, and to determine whether or not this form of antigen is ignored. Chicks and turkey poults were fed solutions containing bovine serum albumin (BSA), porcine serum albumin, beta-lactoglobulin or bovine hemoglobin over a period of 6 days (25mg/chick/day). At different time points after feeding serum and bile were examined for presence of specific antibodies by ELISA. Surprisingly, the fed antigens induced robust antibody responses in the absence of added adjuvant. This immune response was further characterised to show that (1) a daily feeding regimen was more immunogenic than single dose feedings, (2) by using a daily feeding regimen, as little as 2mg/chick/day was fully immunogenic, (3) effective immunization was attained in chicks older than 10 day of age, (4) the main antibody class in the serum was IgG, and (5) high IgA levels were detected in the bile after booster feedings. These observations are difficult to reconcile with current concepts on peripheral tolerance to innocuous antigens, and indicate that the bird regulates tolerance and response in a manner different from that described in mammals.

Impaired T lymphocyte immune response in vitamin A depleted rats and chicks

Vitamin A deficiency results in decreased immune responses; the objective of the present study was to investigate the involvement of T lymphocytes in the depression of immune responses resulting from vitamin A depletion. This objective was achieved by evaluating antigen-specific T lymphocyte proliferative responses in vitro as vitamin A depletion developed. The evaluation was performed in both rat and chick to examine the generality of immune effects due to vitamin A depletion. Our findings show that vitamin A depletion led to severe impairment of T lymphocyte activity in both animal models, and that this was directly related to the vitamin A status in both species. Immune response impairment was found to precede other manifestations of vitamin A deficiency, and was rapidly corrected by feeding retinyl acetate boluses. This implied a possible regulatory, rather than constitutive, role of vitamin A in immune responsiveness.

Regional and global changes in TCRαβ T cell repertoires in the gut are dependent upon the complexity of the enteric microflora.

The repertoire of gut associated T cells is shaped by exposure to microbes, including the natural enteric microflora. Previous studies compared the repertoire of gut associated T cell populations in germ free (GF) and conventional mammals often focussing on intra-epithelial lymphocyte compartments. Using GF, conventional and monocolonised (gnotobiotic) chickens and chicken TCRbeta-repertoire analysis techniques, we determined the influence of microbial status on global and regional enteric TCRbeta repertoires. The gut of conventionally reared chickens exhibited non-Gaussian distributions of CDR3-lengths with some shared over-represented peaks in neighbouring gut segments. Sequence analysis revealed local clonal over-representation. Germ-free chickens exhibited a polyclonal, non-selected population of T cells in the spleen and in the gut. In contrast, gnotobiotic chickens exhibited a biased repertoire with shared clones evident throughout the gut. These data indicate the dramatic influence of enteric microflora complexity on the profile of TCRbeta repertoire in the gut at local and global levels.

The effect of chronic feeding of diacetoxyscirpenol and T-2 toxin on performance, health, small intestinal physiology and antibody production in turkey poults

1. The effects of feeding T-2 toxin or diacetoxyscirpenol (DAS) at levels up to 1 ppm for 32 d on performance, health, small intestinal physiology and immune response to enteral and parenteral immunisation were examined in young poults. 2. Slight improvement in growth was observed in some groups of poults fed T-2 or DAS mycotoxins for 32 d, with no change in feed efficiency. Feeding both T-2 and DAS resulted in oral lesions which had maximal severity after 7-15 d. 3. Mild intestinal changes were observed at 32 d but no pathological or histopathological lesions were found. Both mycotoxins altered small intestinal morphology, especially in the jejunum where villi were shorter and thinner. In addition, both DAS and T-2 mycotoxins enhanced the proportion of proliferating cells both in the crypts and along the villi. Migration rates were reduced in the jejunum of poults fed T-2 toxin but did not change in the duodenum or in poults fed DAS. 4. No significant effects of T-2 or DAS were observed on antibody production to antigens administered by enteral or parenteral routes. 5. This study indicates that tricothecene toxins at concentrations of up to 1 ppm for more than 30 d influenced small intestinal morphology but did not affect growth or antibody production.