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Published on: October 9, 2011
The phenotype and phagocytic activity of macrophages during maedi-visna virus infection
1Department of Veterinary Pathology, University of Edinburgh, Summerhall, UK.
Abstract:
Macrophages from maedi-visna virus (MVV) infected sheep have been shown to have an activated phenotype from sites of lesions in vivo. Here we have looked at the direct effect of virus infection on macrophage phenotype and activity in vitro by flow cytometry. There was no significant difference in the expression of several surface markers (CD4, CD8, MHC Class I, MHC Class II, lymphocyte function associated antigen(LFA)-1 and LFA-3) on monocyte-derived macrophages (MDM) by 5 days post MVV infection. In contrast the phagocytic activity of MVV-infected MDM for the yeast Candida utilis and erythrocytes was decreased by 5 days p.i. although the surface binding of erythrocytes was not affected. Interestingly, an activated phenotype was seen on alveolar macrophages (AM) from sheep with maedi (surface expression of MHC Class I, Class II and LFA-1 was increased), but there was no difference in the binding and phagocytosis of erythrocytes by these cells. However the binding and phagocytosis of the bacterium, Pasteurella hemolytica was increased with AM from MVV-infected sheep without lesions. Similarly there was no significant difference in the phagocytic and erythrocyte rosetting activity between fresh monocytes from MVV-infected and uninfected control sheep. Therefore the phenotype of macrophages taken from sites of lesions caused by MVV does not correspond to a direct effect by the virus on these cells or to particular activities of the macrophages.
Insights
Maedi-visna virus (MVV) infection in sheep does not directly alter macrophage phenotype or activity in vitro. While some macrophages show activation markers, their phagocytic capacity for yeast and erythrocytes is reduced, not enhanced by the virus.
Area of Science:
- Veterinary Virology
- Immunology
- Sheep Pathology
Background:
- Maedi-visna virus (MVV) causes lesions in sheep, associated with activated macrophages in vivo.
- The direct impact of MVV infection on macrophage phenotype and function remains unclear.
Purpose of the Study:
- To investigate the direct effects of MVV infection on macrophage phenotype and phagocytic activity in vitro.
- To compare the in vitro effects of MVV with in vivo observations of activated macrophages.
Main Methods:
- Flow cytometry was used to analyze surface marker expression on monocyte-derived macrophages (MDM) and alveolar macrophages (AM).
- Phagocytic activity assays were performed using yeast (Candida utilis) and erythrocytes.
- Bacterial phagocytosis (Pasteurella hemolytica) was assessed in AM from infected sheep.
Main Results:
- MVV infection did not alter key surface markers (CD4, CD8, MHC I/II, LFA-1/3) on MDM in vitro.
- Phagocytosis of yeast and erythrocytes by MVV-infected MDM was reduced, while erythrocyte binding was unaffected.
- Alveolar macrophages from infected sheep showed increased MHC I/II and LFA-1 expression but no change in erythrocyte phagocytosis.
- AM from MVV-infected sheep without lesions exhibited increased binding and phagocytosis of Pasteurella hemolytica.
Conclusions:
- The activated macrophage phenotype observed at MVV lesion sites in vivo does not result from a direct viral effect on macrophage phenotype or activity.
- The virus may indirectly influence macrophage function or specific macrophage subsets may be involved in the in vivo response.
