Differential expression of complement receptors CR1/2 and CR4 by murine M1 and M2 macrophages.

Macrophages polarize into functionally divergent phenotypes - M1 and M2 - which express distinct receptors. These cells are known to express complement receptors, including CR1, CR3, and CR4. However, whether these complement receptors are differentially expressed on M1 and M2 macrophages is not yet known. Herein, we have examined the expression of CR1 to CR4 on murine bone marrow-derived M1 (stimulated with IFN-γ or LPS) and M2 (stimulated with IL-4 or IL-4 + IL-13) macrophages. We show that M1 cells exhibit increased expression of CR1/2, whereas M2 cells display the higher expression of CR4; CR3 is equally expressed on both the phenotypes. Thus, M1 cells are CR1/2+CR4+, and M2 are CR1/2-CR4+. Functional probing of these cells for their phagocytic ability indicates that M1 cells, which express higher CR1/2, internalize a significantly greater number of C3b-opsonized erythrocytes. Both M1 and M2 cells, on the other hand, internalize iC3b-opsonized erythrocytes to a similar extent. Interestingly, the phagocytic receptor involved in phagocytosis of iC3b-opsonized erythrocytes is only CR3 with no contribution of CR4. We, thus, propose that complement receptor expression can be used in combination with the expression of other known polarization markers to better locate a macrophage along its phenotypic spectrum.

Selective recruitment of nucleoporins on vaccinia virus factories and the role of Nup358 in viral infection.

Vaccinia virus (VACV), a member of the Poxviridae family, uses cytoplasmic factories for its replication. Recent studies indicated that VACV infection requires a set of nucleoporins. However, how the nucleoporins contribute to viral life cycle remains unclear. Here, we report that the nucleoporins Nup62 and Nup358 localize to the cytoplasmic viral factories (VFs). Nup358 was targeted to the VFs at 6h post-infection (hpi), whereas Nup62, along with the previously reported translation factors such as eIF4E, eIF3η and G3BP1, was recruited to the VFs at 8 hpi. Nup358 depletion led to a decrease in the size and number of viral factories and reduction in viral yield. Further studies showed that Nup358 is involved in recruiting Nup62 and eIF4E to the VFs. Collectively, our results reveal spatio-temporal regulation in the recruitment of nucleoporins and translation factors to VFs, and particularly the importance of Nup358 in VACV infection.