Interaction of PRRS virus with bone marrow monocyte subsets.

PRRSV can replicate for months in lymphoid organs leading to persistent host infections. Porcine bone marrow comprises two major monocyte subsets, one of which expresses CD163 and CD169, two receptors involved in the entry of PRRSV in macrophages. In this study, we investigate the permissiveness of these subsets to PRRSV infection. PRRSV replicates efficiently in BM CD163+ monocytes reaching titers similar to those obtained in alveolar macrophages, but with a delayed kinetics. Infection of BM CD163- monocytes was variable and yielded lower titers. This may be related with the capacity of BM CD163- monocytes to differentiate into CD163+ CD169+ cells after culture in presence of M-CSF. Both subsets secreted IL-8 in response to virus but CD163+ cells tended to produce higher amounts. The infection of BM monocytes by PRRSV may contribute to persistence of the virus in this compartment and to hematological disorders found in infected animals such as the reduction in the number of peripheral blood monocytes.