Comparison of Infectious Bronchitis Virus (IBV) Pathogenesis and Host Responses in Young Male and Female Chickens

Abstract

Infectious bronchitis virus (IBV) is an avian coronavirus that causes a disease in chickens known as infectious bronchitis (IB). The pathogenesis of IBV and the host immune responses against it depend on multiple factors such as the IBV variant, breed and age of the chicken, and the environment provided by the management. Since there is limited knowledge about the influence of the sex of chickens in the pathogenesis of IBV, in this study we aim to compare IBV pathogenesis and host immune responses in young male and female chickens. One-week-old specific pathogen-free (SPF) White Leghorn male and female chickens were infected with Canadian Delmarva (DMV)/1639 IBV variant at a dose of 1 × 106 embryo infectious dose (EID)50 by the oculo-nasal route while maintaining uninfected controls, and these chickens were euthanized and sampled 4- and 11-days post-infection (dpi). No significant difference was observed between the infected male and female chickens in IBV shedding, IBV genome load in the trachea, lung, kidney, bursa of Fabricius (BF), thymus, spleen, and cecal tonsils (CT), and IBV-induced lesion in all the examined tissues at both 4 and 11 dpi. In addition, there was no significant difference in the percentage of IBV immune-positive area observed between the infected male and female chickens in all tissues except for the kidney, which expressed an increased level of IBV antigen in infected males compared with females at both 4 and 11 dpi. The percentage of B lymphocytes was not significantly different between infected male and female chickens in all the examined tissues. The percentage of CD8+ T cells was not significantly different between infected male and female chickens in all the examined tissues except in the trachea at 11 dpi, where female chickens had higher recruitment when compared with male chickens. Overall, although most of the findings of this study suggest that the sex of chickens does not play a significant role in the pathogenesis of IBV and the host immune response in young chickens, marginal differences in viral replication and host responses could be observed to indicate that IBV-induced infection in male chickens is more severe.

Differential Impact of Massachusetts, Canadian 4/91, and California (Cal) 1737 Genotypes of Infectious Bronchitis Virus Infection on Lymphoid Organs of Chickens

“…IBV genome load quantification in cDNA samples was performed by qPCR technique, using the Fast SYBR ® Green master mix (Quntabio, Beverly, MA, USA) and CFX 96-c1000 Thermocycler (Bio-Rad Laboratories, Mississauga, ON, Canada) as previously described [ 48 ].…”

“…The thermal cycling conditions were as follows: (I) initial denaturation at 95 °C for 20 s, then 40 cycles of (II) denaturation at 95 °C for 3 s and (III) annealing at 60 °C for 30 s. The sequences of the primers used are as follows: IBV forward 5′GACGGAGGACCTGATGGTAA-3′ and reverse 5′CCCTTCTTCTGCTGATCCTG-3′ [ 48 ].…”

“…The HG, BF, thymus, spleen, and CT harvested from the experimental groups at 3 and 7 dpi and fixed in 10% neutral buffer formalin (VWR International, West Chester, PA, USA) were submitted to the Diagnostic Services Unit (DSU) of the University of Calgary, Faculty of Veterinary Medicine, to obtain hematoxylin and eosin (H&E) stained and unstained slides (positively charged) for immunohistochemistry assay. The histopathological lesion scoring of the HG, BF, thymus, spleen, and CT was performed according to the criteria ( Table 1 ) established previously [ 48 ]. In brief, the scoring was performed as follows: normal (0); mild (1); moderate (2); severe (3) for each criterion, and then the total score was calculated for each organ.…”

“…The immunohistochemical staining for IBV antigens and T-cell and B-cell markers was performed following the methods described by [ 48 , 49 ]. Briefly, after deparaffinization in xylene and rehydration in alcohol, the endogenous peroxidase activity was blocked using a 3% H 2 O 2 solution in methanol for 10 minutes (min).…”