Soluble NS1 antagonizes IgG- and IgA-mediated monocytic phagocytosis of DENV infected cells

Abstract

Dengue virus (DENV) is endemic in over 100 countries, infecting an estimated 400 million individuals every year. Infection with DENV raises a significant antibody response, primarily consisting of antibodies targeting viral (structural) proteins. However, not all DENV antigens are part of the virion itself, as the DENV genome encodes several non-structural (NS) proteins. One of these, NS1, has been shown to be antigenic and is expressed on the membrane of DENV-infected cells. IgG and IgA isotype antibodies that bind NS1 are detectable in serum following DENV infection and are also capable of interacting with Fc receptors expressed on professional phagocytes. Our study aims to determine if NS1-binding IgG and IgA isotype antibodies contribute to the clearance of DENV-infected cells by professional phagocytes through antibody mediated phagocytosis/trogocytosis. Using an in vitro model of trogocytosis we observed that both IgG and IgA isotype antibodies can facilitate facilitating monocytic uptake of DENV NS1 expressing plasma membrane in an additive fashion. This process was dependent on the expression of FcγRI (CD64) and FcαR (CD89) for IgG and IgA mediated membrane uptake, respectively. Furthermore, this process was antagonized by the presence of soluble NS1, suggesting that the production of soluble NS1 by infected cells may serve as an immunological chaff, thereby antagonizing opsonization and clearance of infected cells by NS1-specific IgG and IgA isotype antibodies.

Dengue virus structural proteins are expressed on the surface of DENV-infected cells and are a target for antibody-dependent cellular phagocytosis

“…DENV-structural proteins are expressed on the surface of DENV infected cells. Our group -among others -has observed that DENV-immune sera can opsonize DENV infected cells, facilitating effector functions such as ADCP (20). The antigen that has been primarily cited to facilitate this interaction is NS1, which is known to be highly expressed on the surface of DENV-infected cells.…”

“…Having confirmed both the antigen-specificity and the functional activity of the 4E11 IgG and IgA mAbs, we next endeavored to determine the ability of these antibodies to mediate monocytic phagocytosis of DENV-infected cells. To this end, we utilized a previously described flow cytometry based ADCP assay (20). In brief, this assay begins by labeling the target cells, in this case the DENV3infected CEM.NK R cell line, with the lipophilic dye PKH26.…”

“…These effector mechanisms are thought to play a critical role in the clearance of virally infected cells, as viral antigens expressed on the surface of the infected cells allows for opsonization by virusspecific antibodies and subsequent phagocytic/lytic clearance by FcR expressing leukocytes. Our group has previously shown that DENV NS1 expressed on the surface of DENV-infected cells is readily opsonized by NS1-speific IgG and IgA isotype antibodies, thereby facilitating ADCP (20). However, NS1-specific antibodies are significantly less abundant in DENV-immune individuals than antibodies directed against DENV structural proteins, and prior evidence suggest that DENV structural proteins might also be expressed on the surface of infected cells (21).…”