Intermediate stages in monocyte-macrophage differentiation modulate phenotype and susceptibility to virus infection

The kinetics of monocyte-macrophage differentiation was analysed using two Swine Workshop Cluster (SWC) CD molecules: SWC1 and SWC9. Myeloid cells wer e selected by labelling for the common myeloid antigen, SWC3. Confirmation of macrophage identification used acid phosphatase and phagocytosis activit ies. During differentiation, SWC1 was gradually lost. SWC9 was absent on mo nocytes but up-regulated early. Consequently, monocytes were SWCl+ SWC9(-) and macrophages were SWC1(-) SWC9(+). An additional, intermediate, cell pop ulation was identified as SWC1(+) SWC9(+). Size and granularity characteris tics mirrored the monocyte, macrophage and intermediate-cell phenotypes. Ov erall, SWC9 up-regulation was central in macrophage differentiation and dep endent on plasma factors. The concomitant loss of SWC1 was independent of t hese factors, but always associated with mature macrophages. Upon up-regula tion of SWC9, the SWC1(+) SWC9(+) intermediate monocytic cells became susce ptible to African swine fever virus infection. These results demonstrate th e heterogeneity of monocytic cell differentiation and the importance of the se characteristics for interaction with monocytotropic viruses.