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Lysis of myelocytes in chickens infected with infectious bursal disease virus
1Department of Veterinary Pathology, Faculty of Agriculture, Yamaguchi University, Japan. makoto@agr.yamaguchi-u.ac.jp
Abstract:
In specific-pathogen-free chickens infected with the highly virulent HPS-2 strain or virulent reference GBF-1 strain of infectious bursal disease virus (IBDV), pathologic changes of the bone marrow were investigated. On histologic examination, bone marrow lesions were prominent in the HPS-2 group but only mild in the GBF-1 group. The bone marrow of the HPS-2 group showed severe lysis and depletion of heterophil myelocytes with pyknotic nuclear alteration 2-3 days after inoculation. On examination with an electron microscope, heterophil myelocytes were characterized by shrinkage of the cytoplasm and peripheral condensation of nuclear chromatin. IBDV particles were not detected in altered myelocytes. A terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling method demonstrated a positive reaction in only heterophil myelocytes. In contrast, nucleosomal DNA fragmentation in HPS-2-infected bone marrow cells was indiscernible by agarose gel electrophoresis. These findings indicate that lysis of bone marrow cells is selectively induced in heterophil myelocytes at an early stage after IBDV infection and independent of virus replication.
Insights
Infectious Bursal Disease Virus (IBDV) selectively targets and destroys heterophil myelocytes in chicken bone marrow early in infection. This bone marrow cell lysis occurs independently of virus replication, impacting the immune response.
Area of Science:
- Veterinary Pathology
- Virology
- Immunology
Background:
- Infectious Bursal Disease Virus (IBDV) is a significant pathogen affecting poultry.
- Understanding IBDV's impact on host tissues, particularly the bone marrow, is crucial for disease management.
Purpose of the Study:
- To investigate the pathological changes in chicken bone marrow following infection with different strains of IBDV.
- To characterize the specific cell types affected and the mechanism of cell damage.
Main Methods:
- Histological examination of bone marrow from specific-pathogen-free chickens infected with HPS-2 or GBF-1 IBDV strains.
- Electron microscopy to visualize cellular alterations.
- Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) assay.
- Agarose gel electrophoresis to detect DNA fragmentation.
Main Results:
- Prominent bone marrow lesions were observed in chickens infected with the highly virulent HPS-2 strain compared to the GBF-1 strain.
- Severe lysis and depletion of heterophil myelocytes with nuclear alterations occurred 2-3 days post-inoculation with HPS-2.
- Electron microscopy revealed cytoplasmic shrinkage and chromatin condensation in affected heterophil myelocytes.
- TUNEL assay confirmed apoptosis specifically in heterophil myelocytes, while DNA fragmentation was not evident via gel electrophoresis.
- IBDV particles were not detected within the altered myelocytes.
Conclusions:
- IBDV infection selectively induces lysis of heterophil myelocytes in chicken bone marrow.
- This pathological process occurs early in infection and is independent of active virus replication within the affected cells.
- The findings highlight a specific mechanism of immune cell destruction by IBDV, potentially impacting the host's innate immune response.