Characterization of the interaction of African swine fever virus with monocytes and derived macrophage subsets

Abstract

African swine fever (ASF) is a devastating disease for which there is no vaccine available. The ASF virus (ASFV) primarily infects cells of the myeloid lineage and this tropism is thought to be crucial for disease pathogenesis. A detailed in vitro characterization of the interactions of a virulent Sardinian isolate (22653/14) and a tissue culture adapted avirulent strain (BA71V) of ASFV with porcine monocytes, un-activated (moMΦ), classically (moM1) and alternatively (moM2) activated monocyte-derived macrophages was conducted in an attempt to better understand this relationship. Using a multiplicity-of-infection (MOI) of 1, both viruses were able to infect monocytes and macrophage subsets, but BA71V presented a reduced ability to infect moM1 compared to 22653/14, with higher expression of early compared to late proteins. Using an MOI of 0.01, only 22653/14 was able to replicate in all the macrophage subsets, with initially lowest in moM1 and moM2. No differences were observed in the expression of CD163 between ASFV infected and uninfected bystander cells. ASFV down-regulated CD16 expression but did not modulate MHC class II levels in monocytes and macrophage subsets. BA71V-infected but not 22653/14-infected moMΦ and moM2 presented with a reduced expression of MHC class I compared to the mock-infected controls. Higher levels of IL-18, IL1-β and IL-1α were released from moM1 after infection with BA71V compared to 22653/14 or mock-infected control. These results revealed differences between these ASFV strains, suggesting that virulent isolates have evolved mechanisms to counteract activated macrophages responses, promoting their survival, dissemination in the host and so ASF pathogenesis.

Comparison of Macrophage Responses to African Swine Fever Viruses Reveals that the NH/P68 Strain is Associated with Enhanced Sensitivity to Type I IFN and Cytokine Responses from Classically Activated Macrophages

“…moMΦ infected with the virulent genotype I Sardinian strains (Nu81.2 and 22653/14) presented a slightly higher MHC class I expression, albeit without statistical significance ( Figure 5). Infection with both genotype II (Arm07) and genotype IX (Ken06.Bus) virulent isolates induced MHC class I down-regulation (observed In our previous work we observed that the attenuated BA71V also inhibited MHC class I expression on moMΦ [6], thus we wanted to determine whether the absence of MHC class I down-regulation following 22635/14 infection was a strain-specific effect. moMΦ infected with the virulent genotype I Sardinian strains (Nu81.2 and 22653/14) presented a slightly higher MHC class I expression, albeit without statistical significance ( Figure 5).…”

“…Differences were also observed between infected and bystander cells, suggesting that MHC class I modulation is a direct consequence of virus infection ( Figure 4B). In our previous work we observed that the attenuated BA71V also inhibited MHC class I expression on moMΦ [6], thus we wanted to determine whether the absence of MHC class I downregulation following 22635/14 infection was a strain-specific effect. moMΦ infected with the virulent genotype I Sardinian strains (Nu81.2 and 22653/14) presented a slightly higher MHC class I expression, albeit without statistical significance ( Figure 5).…”

“…Macrophages are the primary target cell for ASFV and provide a first line of defense against pathogens, thus their interaction with ASFV is of major importance. As we recently reviewed, in vitro studies on macrophages showed that attenuated ASFV strains induce enhanced expression of cytokines (IFN-α, IFN-β, IL-1β, IL-12, IL-18, TNF-α) and chemokines (CCL4, CXCL8, CXCL10) compared to highly virulent strains [2][3][4][5][6][7]. Both virulent and attenuated ASFV down-regulated CD14 and CD16 expressions on infected macrophages, which may affect their anti-microbial/viral activity [6][7][8].…”

“…As we recently reviewed, in vitro studies on macrophages showed that attenuated ASFV strains induce enhanced expression of cytokines (IFN-α, IFN-β, IL-1β, IL-12, IL-18, TNF-α) and chemokines (CCL4, CXCL8, CXCL10) compared to highly virulent strains [2][3][4][5][6][7]. Both virulent and attenuated ASFV down-regulated CD14 and CD16 expressions on infected macrophages, which may affect their anti-microbial/viral activity [6][7][8]. Overall, these studies suggest that virulent ASFV isolates have evolved mechanisms to counteract macrophage responses, whereas expression of key cytokines and chemokines from macrophages in response to attenuated ASFV strains could enhance the induction of innate immune responses and promote the induction of effective adaptive immune responses [7].…”

Gaps in African swine fever: Analysis and priorities

“…A recent study conducted by Franzoni et al. () showed that virulent isolates have evolved mechanisms to counteract activated macrophage response promoting viral survival, dissemination in the host and pathogenesis. More detailed characterization of interactions between ASFV and macrophages and other cells in the host may provide new insights into how to induce a protective immune response.…”