Impact of Maternal Antibodies on Infectious Bronchitis Virus (IBV) Infection in Primary and Secondary Lymphoid Organs of Chickens

Abstract

Infectious bronchitis virus (IBV) causes infectious bronchitis disease in chickens. IBV primarily infects the upper respiratory tract and then disseminates to other body systems including gastrointestinal, reproductive, and urinary systems. Unlike original IBV serotypes, the novel IBV variants target lymphoid organs, but information on this is scarce. In this study, we aim to evaluate the impact of the presence of maternal antibodies on IBV infection in primary and secondary lymphoid organs. Maternal antibody free, specific pathogen free (SPF) hens were divided into vaccinated and non-vaccinated groups. The progeny male chicks from these hens were divided into four groups; vaccinated challenged (VC), non-vaccinated challenged (NVC), vaccinated non-challenged (VNC), and non-vaccinated non-challenged (NVNC). The challenge groups were given 1 × 10⁶ embryo infectious dose (EID)₅₀ of IBV Delmarva (DMV)/1639 by the oculo-nasal route and non-challenge groups were given saline. The serum anti-IBV antibody titer was significantly higher in challenged groups compared to non-challenged groups. The IBV genome load was significantly lower in the VC group than NVC group in oropharyngeal and cloacal swabs and in bursa of Fabricius (BF) and cecal tonsils (CT). The histopathological lesion scores were significantly lower in VC group than NVC group in BF and CT. These findings suggest that the presence of maternal antibody in chicks could provide some degree of protection against IBV infection in BF and CT.

Keywords: bursa of Fabricius; cecal tonsils; infectious bronchitis virus; maternal antibody; spleen; thymus.

Figure 1

Summary of the experimental design used in this study.

Figure 2

IBV antibody titers in serum of (a) pre-challenge birds (n = 16/group) at the day of hatching and in serum of post-challenge birds (n = 8/group) at (b) 3 and (c) 7 dpi. Mean antibody titers of pre-challenged birds were compared using unpaired t test. Mean antibody titers in post-challenged birds at 3 and 7 dpi were compared using one-way ANOVA followed by Tukey’s multiple comparisons test. The error bars represent the standard deviation (SD). Statistical significance: ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 3

IBV genome loads in (a) OP and (b) CL swabs at 3 and 7 dpi following challenge with the Canadian DMV/1639 IBV strain (IBV/Ck/Can/17–036989). The average starting IBV genome load was quantified per 100 ng of the extracted RNA and comparisons between groups was performed using one-way ANOVA followed by Tukey’s multiple comparisons test, and the error bars represent the SD. Statistical significance: **** p < 0.0001.

Figure 4

IBV genome loads in (a) trachea, (b) lung, (c) kidney, (d) bursa of Fabricius, (e) thymus, (f) cecal tonsils, (g) spleen, (h) pancreas, and (i) duodenum at 3 and 7 dpi following challenge with the Canadian DMV/1639 IBV strain. The mean IBV genome load was quantified per 100 ng of the extracted RNA and comparisons between groups were determined using one-way ANOVA followed by Tukey’s multiple comparisons test, and the error bars represent the SD. Statistical significance: * p < 0.05, ** p < 0.01, **** p < 0.0001.

Figure 5

Immunohistochemical analysis of IBV nucleoprotein in trachea and lung at 3 and 7 dpi. IBV nucleoprotein is expressed as brown intra-cytoplasmic staining in (A–H) trachea and (I–P) lung.

Figure 6

Immunohistochemical analysis of IBV nucleoprotein in bursa of Fabricius (BF) and cecal tonsils (CT) at 3 and 7 dpi. IBV nucleoprotein is expressed as brown intra-cytoplasmic staining in (A–H) BF and (I–P) CT.

Figure 7

Immunohistochemical analysis of IBV nucleoprotein in kidney and spleen at 3 and 7 dpi. IBV nucleoprotein is expressed as brown intra-cytoplasmic staining in (A–H) kidney and (I–P) spleen.

Figure 8

Immunohistochemical analysis of IBV nucleoprotein in duodenum and pancreas at 3 and 7 dpi. IBV nucleoprotein is expressed as brown intra-cytoplasmic staining in (A–H) duodenum and (I–P) pancreas.

Figure 9

Lesion scores in (a) trachea, (b) lung, (c) kidney, (d) pancreas, (e) bursa of Fabricius, (f) cecal tonsils, and (g) duodenum at 3 and 7 dpi following challenge with the Canadian DMV/1639 IBV strain. Error bars represent values expressed as median with interquartile range and were analyzed using two-way ANOVA followed by Tukeys multiple comparisons and the Mann–Whitney test to compare the VC and NVC groups. Significance: * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 10

Photomicrographs of trachea and lung representing the four experimental groups. (C,D,G,H) Trachea shows normal histological pictures. (A,B) Trachea shows epithelial lining degeneration and necrosis, and mild mucosal and submucosal mononuclear cell infiltration. (E,F) Trachea shows marked degeneration and necrosis of epithelial lining with ballooning of mucus cells and severe mucosal and submucosal mononuclear inflammatory cell aggregation. (K,L,O,P) Lung shows normal histological architecture. (I,J) Lung shows mild peribronchial mononuclear inflammatory cell infiltration with degenerative changes in their epithelium lining. (M,N) Lung shows moderate bronchitis.

Figure 11

Photomicrographs of kidney and pancreas representing the four experimental groups. (C,D,G,H) Kidney shows normal histological structure. (A) Kidney shows mild vacuolar degeneration of epithelium lining renal tubules. (B,E) Kidney shows focal interstitial lumphoplasmocytic nephritis. (F) Kidney shows diffuse lymphoplasmocytic interstitial nephritis. (K,L,M,O,P) Pancreas shows normal histological picture. (I) Pancreas shows mild lymphocytic infiltration with degeneration and necrosis of acinar cells. (J) Pancreas shows focal lymphocytic infiltration, degeneration, and necrosis of acinar cells and dilation of the intra lobular duct wall with periductular heterophilic aggregation. (N) Pancreas shows lymphocytic infiltration.

Figure 12

Photomicrographs of bursa of Fabricius (BF) and cecal tonsils (CT). (C,D,G,H) BF shows normal histological structure. (A) BF shows mild lining epithelial hyperplasia with degeneration and necrosis of the few cells. (B) BF shows degeneration and necrosis of its epithelium lining with sub epithelium and interfollicular mononuclear cell and heterophils aggregation. (E) BF shows multifocal areas of epithelial cell hyperplasia. (F) BF shows severe hyperplasia of lining epithelium with squamous cell metaplasia with apoptosis and necrosis of some of them. (K,L,O,P) CT shows normal histological findings. (I) CT shows severe lymphoepithelial necrosis and sub-epithelial inflammatory cells aggregation mainly with lymphocytes and macrophages (J) CT shows moderate lymphoepithelial necrosis with lymphoidal apoptosis in the interfollicular area. (M) CT shows severe lymphoepithelial necrosis with sub-epithelial heterophils, lymphocytes, and macrophages aggregation. (N) CT shows vacuolar degeneration, and necrosis of lymphoepithelium with lymphoidal depletion in interfollicular tissue.