Elsevier

Virus Research

Volume 113, Issue 1, October 2005, Pages 44-50
Virus Research

Infection and activation of bursal macrophages by virulent infectious bursal disease virus

https://doi.org/10.1016/j.virusres.2005.04.014Get rights and content

Abstract

In this study the effect of infectious bursal disease virus (IBDV) on bursal macrophages during the acute phase of the infection was examined. Specific-pathogen-free (SPF) chickens were exposed to virulent IBDV and bursal adherent cells were examined by immunohistochemisrty and RT-PCR for virus infection and by real-time quantitative RT-PCR (qRT-PCR) for mRNA transcripts of proinflammatory cytokines and iNOS. Viral genome was detected in bursal macrophages at 3, 5 and 7 days post-infection (dpi). Immuno-histochemical staining revealed double positive cells for KUL01 (macrophage marker) and intracellular viral proteins, showing viral replication in bursal macrophages of infected chickens. We noted a significant decrease in the total number of bursal macrophages in infected chickens, probably due to the lysis of infected cells. However, likely due to extensive necrosis of B cells, the relative proportion of bursal macrophages was significantly higher (P < 0.05) in infected birds at 3 and 5 dpi than in controls. Among the cytokines examined, IL-6 showed the greatest upregulation (100-fold increase) at 3 dpi. Expression of IL-1β was maximum at 3 dpi whereas IL-18 expression was highest at 1 dpi. Enhanced expression of iNOS mRNA was observed at 5 dpi. Increased expression of the proinflammatory cytokines and iNOS correlated well with the presence of the inflammatory response in the infected bursa. These data suggested that B cells may not be the sole targets for the virus; macrophages and possibly other cells may serve as host for IBDV.

Introduction

Infectious bursal disease is one of the most important viral diseases affecting the poultry industry worldwide (Lukert and Saif, 2003). The causative agent, IBDV, belongs to the family Birnaviridae. This virus causes an acute, highly contagious and immunosuppressive disease in chickens (Lukert and Saif, 2003). The virus infects and destroys actively dividing IgM-bearing B cells in the bursa of Fabricius (Hirai et al., 1981, Rodenberg et al., 1994). Infection with IBDV compromises both humoral and cellular immunity (Sharma et al., 1989). Immunosuppression induced by IBDV is the primary cause of economic loss associated with the virus.

Exposure to IBDV results in an acute, self-limiting disease. Under experimental conditions, the acute disease lasts for about a week. During this acute phase, replicating virus causes extensive destruction of bursal follicles (Tanimura and Sharma, 1997) resulting in reduction of circulating IgM+ B cells (Hirai et al., 1981, Rodenberg et al., 1994). Replication of IBDV in the bursa is accompanied by influx of T cells (Tanimura and Sharma, 1997, Kim et al., 1999, Kim et al., 2000, Sharma et al., 2000). Although the bursal T cells were activated and proliferated in vitro when stimulated by purified IBDV, there was strong evidence that T cells did not serve as targets for infection and replication of IBDV (Kim et al., 2000). There are reports that macrophages and monocytes may be susceptible to infection with the virus (Käufer and Weiss, 1976, Käufer and Weiss, 1980, Müller, 1986, Burkhardt and Muller, 1987, Komine et al., 1989, Inoue et al., 1992, Lam, 1998). We noted earlier that spleen cells from IBDV exposed chickens during acute infection had enhanced gene expression of IFNα/β, IL-6, cMGF, 9E3/CEF4 (IL-8) and produced elevated levels of nitric oxide (Kim et al., 1998). Macrophages have been proposed to serve as virus carriers from the site of infection in the gut to the bursa and other peripheral tissues (Käufer and Weiss, 1976, Sharma and Lee, 1983, Kim et al., 1998, Lam, 1998, van den Berg, 2000).

Macrophages are important effectors of the innate immune system. Macrophages produce proinflammatory cytokines such as IL-6, IL-1β and TNF-α, which are important in initiating an inflammatory response at the site of infection. The local inflammatory response recruits other phagocytic and non-phagocytic lymphoid cells important for immunity. Thus, proinflammatory cytokines are a natural response to infection and may be beneficial to the host defense. However, when expressed in excess, proinflammatory cytokines may enhance tissue destruction, impede recovery and harm the host. Recent studies suggest that hyperactivity of macrophage and overproduction of TNF-α may lead to autologous cell destruction and T cell-mediated autoimmune diseases (O'Shea et al., 2002).

The objective of the present study was to examine the interaction of IBDV with bursal macrophages. Specifically, we examined the effect of the virus on relative proportion of macrophages in the bursa, replication of the virus within macrophages and upregulation of the genes encoding proinflammatory cytokines and iNOS.

Section snippets

Animals, virus and antibodies

Specific-pathogen-free (SPF) eggs were obtained from HyVac (Gowrie, IA). The eggs were hatched in an incubator under the supervision of the Animal Facility Management, University of Minnesota. After hatching, 1-day-old chicks were housed in Horsfall–Bauer-type isolators. At 21 days of age, chickens were inoculated with 104 50% egg infectious dose (EID50) of the IM strain of IBDV (IM-IBDV) or phosphate buffered saline (PBS) by the intraocular route. IM-IBDV was originally obtained from Dr. R.W.

Response of chickens to IBDV

Inoculation of chickens with IM-IBDV resulted in a typical acute response to the virus. Chickens inoculated with IBDV had enlarged and pale bursa at 3 and 5 dpi. Microscopically, severe follicular destruction was observed at 3 dpi which persisted till 5 dpi (the last day of observation) (Fig. 1). Sections of bursae collected at 1, 3, and 5 dpi were examined for the presence of IBDV antigen by immunohistochemistry. Peroxidase-stained cells (brown) positive for viral proteins were observed in bursal

Discussion

This is the first attempt to show the involvement of bursal macrophages in the pathogenesis of IBDV. Chickens were infected with virulent IBDV and the macrophages recovered from the bursa during the first week of infection were examined. We noted that the total number of bursal macrophages was significantly lower in the infected birds compared to that in controls (P < 0.05). However, the relative proportion of these cells within the bursae was significantly higher in infected birds than in

References (45)

  • T.L. Pertile et al.

    Reovirus infection in chickens primes splenic adherent macrophages to produce nitric oxide in response to T cell-produced factors

    Cell Immunol.

    (1995)
  • S. Romagnani

    Induction of Th1 and Th2 responses: a key role for the ‘natural’ immune response?

    Immunol. Today

    (1992)
  • J.M. Sharma et al.

    Infectious bursal disease virus of chickens: pathogenesis and immunosuppression

    Dev. Comp. Immunol.

    (2000)
  • J.W. Sijben et al.

    Early in vivo cytokine genes expression in chickens after challenge with Salmonella typhimurium lipopolysaccharide and modulation by dietary n-3 polyunsaturated fatty acids

    Dev. Comp. Immunol.

    (2003)
  • H.Y. Yeh et al.

    Protective immunity against infectious bursal disease virus in chickens in the absence of virus-specific antibodies

    Vet. Immunol. Immunopathol.

    (2002)
  • A. Aderem et al.

    Mechanisms of phagocytosis in macrophages

    Annu. Rev. Immunol.

    (1999)
  • A.D. Barrow et al.

    Infection of macrophages by a lymphotropic herpesvirus: a new tropism for Marek's disease virus

    J. Gen. Virol.

    (2003)
  • E. Burkhardt et al.

    Susceptibility of chicken blood lymphoblasts and monocytes to infectious bursal disease virus (IBDV)

    Arch. Virol.

    (1987)
  • K. Hirai et al.

    Sequential changes in the number of surface immunoglobulin-bearing B lymphocytes in infectious bursal disease virus-infected chickens

    Avian Dis.

    (1981)
  • M. Inoue et al.

    Susceptibility of chicken monocytic cell lines to infectious bursal disease virus

    J. Vet. Med. Sci.

    (1992)
  • K.W. Jarosinski et al.

    Influence of genetic resistance of the chicken and virulence of Marek's disease virus (MDV) on nitric oxide responses after MDV infection

    Avian Dis.

    (2002)
  • S.H. Jeurissen et al.

    Defence mechanisms against viral infection in poultry: a review

    Vet. Q.

    (2000)
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