Characterization of Immune and Enteric Systems of Broilers after Imunosupression with Dexamethasone

Abstract

Background: Bursa of Fabricius (BF) and the thymus are primary lymphoid organs of poultry and play a major role in avian immunity. Enteric system is also involved in immunity. Several pathologic conditions directly impact BF and thymus size, and also affect intestinal parameters. Besides, there are several immune system depressor agents which affect birds. The selection of glucocorticoid as inducer of immunosuppression is applied in many experiments; however there are few studies that are applied to the reality in the field. In this context, the aim of this study was to evaluate the effects of dexamethasone as an inducer of immunosuppression on lymphoid organs and microscopic structures of the jejunum.

Materials, Methods & Results: One-day-old chicks were used as a control group (n = 8) and the treated group (n = 25) received intramuscular dexamethasone on 21, 23, 24 and 26 day-old. Control birds and treated birds were euthanized 8, 16, 24, 32 and 40 h after inoculation; four control birds and six treated birds were euthanized on the eighth day after the last inoculation. Thymus, BF and jejunum were collected during the necropsy. The selected organs were processed, stained with hematoxylin and eosin and photographed. The BF and thymus cuts were evaluated by three histopathologists to determine the depletion score. Ten villi of each jejunum were evaluated for width and length of villi, depth crypt, microvillus length, enterocyte length of each villus, and wall thickness. Treated birds presented a mean weight lower than control group during all the experiment. The mean weight and the relative weight of the BF and thymus of control birds were significantly higher than treated ones. The lymphocyte depletion in BF and thymus scores differed significantly between groups, being higher in the group challenged with dexamethasone. There were no significant differences between groups for depth of crypt, height of core and height of microvilli. The intestines of the control group had higher mean values for length of villi, width of villi, height of enterocyte and thickness of wall. Significant correlation between weight of thymus and weight of BF, between weight of thymus and weight of bird and between weight of BF and bird weight were found.

Discussion: Easy administration, low cost and the absence of suffering during inoculation make the use of glucocorticoids more advantageous to mimic immunosupression in poultry. Treatment with dexamethasone interfered directly in the weight of the birds. Evaluation of immune response of birds can be performed by the ratio of the BF weight in relation to the weight of the bird, as observed in the present study. The relative weight of the BF of untreated animals varied at all ages between 0.21% and 0.29%. It was also observed that the relative weight of BF and thymus in immunosuppressed birds tended to increase according to the end of the treatment. Depletion scores were higher in thymus, suggesting that glucocorticoid promoted more harmful effects on this organ. Dexamethasone had negative influence on length of villus, once mean value was 13% lower than those of control group. Width of villus and height of enterocyte core of treatment group were lower than those observed in control animals. Coefficient of determination greater than 70% was observed for almost all established relationships, except for the length of villi and weight of the thymus. Administration of dexamethasone promotes significant and negative effects on the gain of weight, length of villi, width of villi and height of enterocytes. These finding are useful for future experiments with controlled immunosuppression induction, once it provides significant information of the secondary effects of glucocorticoids administration in poultry.