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FMDV tropism for dendritic cells

Background: FMDV is known to interact with macrophages, but nothing is known about the interaction of the virus with dendritic cells (DC). This is important considering the critical role played by DC in initiating and controlling both innate and adaptive (specific) immune responses.

Moreover, vaccine design requires that the virus (inactivated viral antigen) interact with the DC in an efficient manner such that the antigen is correctly processed by the DC leading to stimulation of immune defence development. Incorrect interaction of the virus antigen with the DC can lad to destruction of the antigen without stimulation of the immune defences. Accordingly, the aim was to determine the capacity of FMDV to bind to and interact with DC of a natural host the pig.

Results: FMDV binds to monocytes (Mo), macrophages (MF), and dendritic cells (DC) but no virus replication occurs. This interaction was particularly efficient when the virus could employ heparan sulphate (HS) entities on the cell surface, but not when only integrins were available. When HS binding and non-HS-binding virus variants were compared, the former were the more efficiently internalised by the DC. Moreover, DC does not express the avb6 integrin demonstrated in this project to be the main integrin receptor for FMDV.

This importance of HS binding for FMDV interaction with DC was confirmed using dispirotripiperazine (DSTP), a blocker of HS binding. The DSTP blocked the uptake of the HS-binding viruses, demonstrating that these viruses did indeed employ the HS structures on the DC surface for binding and subsequent internalisation by the cells. With the non-HS viruses, these were rapidly internalised by the DC, with a rapid processing rendering antigen detection difficult. Although HS was not employed, and avb6 integrin was not present on the DC, it is likely that these non-HS binding viruses were employing other integrin structures for binding to the DC. None of the integrins currently detectable on porcine cells were involved in this process.

HS-binding virus is internalised by DC within 5 min, becoming distributed within the peripheral cytoplasm within 1hr, and still detectable after 4 hr. This is unaffected by bafilomycin treatment of the cells (inhibits endosomal acidification processes). With the non-HS virus in the presence of bafilomycin, the virus remained around the periphery without being internalised. In the absence of bafilomycin, no virus was detectable. These results suggest that the HS-binding virus enters DCs by an endosomal-independent manner, whereas non-HS virus enters via processes relying on rapid endosomal acidification.

DC can also be transfected with RNA derived from FMDV infectious DNA clones. Low levels of antigen and infectious virus can be detected at 24 hr p.i., but this is processed by the DC within the next 24 hr to become undetectable.

These results are demonstrating that the presence of heparin sulphate binding capacity in an FMDV preparation aids the interaction of the virus with DC, giving HS-binding virus and advantage over non-HS binding virus. This is particularly important considering that the DC do not possess the avb6 integrin demonstrated in this project to be the main integrin receptor for FMDV. It is also important for vaccine manufacturers when their vaccine virus has been cell culture passaged and therefore carrying this HS binding capacity.

The effort towards this TIP also demonstrated that the DC can accommodate RNA transfection, which might prove a usual means of vaccination in the future.

Reported by

INSTITUTE OF VIROLOGY AND IMMUNOPROPHYLAXIS
SENSEMATTSTRASSE 293
3147 MITTELHAUESERN
Switzerland
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