Impact of heterophil granulocyte depletion caused by 5-fluorouracil on infectious bursal disease virus infection in specific pathogen free chickens

Abstract

The purpose of this study was to investigate the influence of the cytostatic drug, 5-fluorouracil (5-FU), which causes depletion of heterophil granulocytes, on clinical symptoms and histological lesions during the progress of infectious bursal disease virus (IBDV) infection in chickens. The aim was to disclose the mechanism behind the clinical disease symptoms. Three groups of specific pathogen free chickens were used for the experiment. Chickens in groups 1 and 3 were pretreated with 5-FU, while chickens in group 2 were treated with a placebo. After 5 days, the chickens in groups 2 and 3 were inoculated with the classical IBDV strain F52/70. Bursae of Fabricius were sampled at fixed intervals, and the progress of the infection was monitored by various histological techniques and reverse transcriptase-polymerase chain reaction (RT-PCR). We found correlation between histological observations and RT-PCR results. In the 5-FU pretreated chickens, IBDV caused only mild clinical symptoms, even though histological alterations similar to alterations caused by IBDV were still observed. The 5-FU pretreatment resulted in severe heterophil granulocyte depletion by days 2 and 3 after infection (post inoculation) and increased numbers of bursal secretory dendritic cells in the medulla of the follicles. IBDV infection seemed to induce fusion of secretory dendritic cells, resulting in formation of multinucleated giant cells, loaded with apoptotic B cells and virus particles associated with granules of bursal secretory dendritic cells. Our results indicate that the heterophil granulocytes together with the bursal secretory dendritic cells contribute to the outbreak and/or progress of clinical symptoms.

Life cycle of chicken bursal secretory dendritic cell (BSDC)

“…Therefore, transmission electron microscopy does not confirm that the primary target of IBDV would be the ERC. The Mal is loaded with viruses, therefore based on our earlier findings, we have proposed that the BSDC is the primary target of IBDV ( Kabell et al, 2006 ), which was confirmed by Yasmin et al (2015) .…”

“…The cytokine storm drives the chB6 positive, but virus-free B cell into the interfollicular space ( Shah et al, 2021 ) which suggests that the B cells are not the primary target of IBDV ( Shah et al, 2021 ). Our earlier studies provide evidence that at least 2 kinds of cells are essential for the clinical outbreak of IBDV infection: intrabursal BSDC and a bone marrow-derived heterophil granulocyte ( Kabell et al, 2006 ). After IBDV infection, the BSDC rapidly transform to Mal and migrate into the cortex, initiating heterophil invasion and subsequently cytokine storm.…”

“…After IBDV infection, the BSDC rapidly transform to Mal and migrate into the cortex, initiating heterophil invasion and subsequently cytokine storm. Before IBDV infection, depletion of the heterophil granulocytes by 5-fluorouracil treatment ( Kogut et al, 1993 ) resulted in mild outbreak of clinical symptoms and survival of chickens ( Kabell et al, 2006 ). In the follicular medulla, the rest of the uninfected B cells undergo nascent apoptosis in the absence of extracellular glycoprotein.…”

Interaction of infectious bursal disease virus with the immune system of poultry

“…The number of the heterophils entering the BF increase with acute IBDV infection (Lam, 1998). Kabell et al (2006) have studied the effect of IBDV after pretreating the three groups with 5-fluorouracil, a placebo and 5-fluorouracil, and the results indicated that heterophil granulocytes, together with the bursal secretory DCs, contribute to the outbreak and may progress clinical symptoms. IBDV in vitro alter the functioning of heterophils, with decreases in cell migration and phagocytic activity whilst it activates cellular oxidative bursts and increases cellular adherence to the IBDV-infected chicken embryo fibroblasts of the heterophils.…”

Effect of Intermediate Plus Vaccine and vvIBDV on Bursa Secretory Cells and Their Glycoprotein Production

“…In the cells of the IFE, we were unable to identify virus particles with IBDV cytochemistry or transmission microscope; however, the presence of malformed granules shows that IBDV infection deeply interferes with the Golgi function, glycosylation. It is not apparent whether the Golgi complex has been influenced directly by the virus or by some biologically active factor(s) released from other infected cells, namely BSDC transformed to Mals [ 13 , 17 ] or heterophil granulocytes [ 20 ] which enter the IFE.…”