Measles Virus-Induced Immunosuppression In Vitro Is Independent of Complex Glycosylation of Viral Glycoproteins and of Hemifusion

Abstract

Expression of the measles virus (MV) F/H complex on the surface of viral particles, infected cells, or cells transfected to express these proteins (presenter cells [PC]) is necessary and sufficient to induce proliferative arrest in both human and rodent lymphoid cells (responder cells [RC]). This inhibition was found to occur independent of apoptosis and soluble mediators excluded by a pore size filter of 200 nm released from either PC or RC. We now show that reactive oxygen intermediates which might be released by RC or PC also do not contribute to MV-induced immunosuppression in vitro. Using an inhibitor of Golgi-resident mannosidases (deoxymannojirimycin), we found that complex glycosylation of the F and H proteins is not required for the induction of proliferative arrest of RC. As revealed by our previous studies, proteolytic cleavage of the MV F protein precursor into its F1 and F2 subunits, but not of F/H-mediated cellular fusion, was found to be required, since fusion-inhibitory peptides such as Z-D-Phe-L-Phe-Gly (Z-fFG) did not interfere with the induction of proliferative inhibition. We now show that Z-fFG inhibits cellular fusion at the stage of hemifusion by preventing lipid mixing of the outer membrane layer. These results provide strong evidence for a receptormediated signal elicited by the MV F/H complex which can be uncoupled from its fusogenic activity is required for the induction of proliferative arrest of human lymphocytes.In the course of acute measles, an efficient virus-specific immune response is generated which leads to viral clearance from the peripheral blood and the establishment of lifelong immunity to reinfection. Paradoxically, measles virus (MV) also causes a marked suppression of the host's immune responses that accounts for high susceptibility to opportunistic infections; that is the major reason for the high rates of measles-related morbidity and mortality worldwide (7). It is a key finding in MV-induced immunosuppression that peripheral blood lymphocytes (PBL) isolated during and for weeks after acute measles largely fail to proliferate in response to mitogenic, allogenic, and recall antigen stimulation (5, 33). Although MV infects cells of the lymphoid/monocytic lineage and induces cell cycle arrest in these cells (21)(22)(23)40), the frequency of infected peripheral blood mononuclear cells (PBMC) is usually low at any stage of the disease. This indicates that the general failure of lymphocytes to response to mitogenic stimulation is not likely to result from directly infection-dependent cell loss or cell cycle arrest. Thus, independent mechanisms such as the release of inhibitory soluble mediators from infected PBMC (12, 36) or surface contactmediated negative signaling between MV glycoproteins and cellular receptor molecules have been suggested. These include MV H-protein-mediated downregulation of CD46 from the surface of uninfected cells or downregulation of interleukin-12 release from uninfected monocytes following CD46 cross-linking by MV or CD46 ligation by specific ant...

Canine Distemper Viruses Expressing a Hemagglutinin without N-Glycans Lose Virulence but Retain Immunosuppression

“…In addition, all nonlethal viruses carrying 5804P H proteins resulted in prolonged inhibition of lymphocyte proliferation, while the virus with the vaccine H protein only transiently interfered with this activity. Our findings confirm previous reports that MeV wild-type H proteins are more immunosuppressive than vaccine H proteins (33), while complex N glycosylation was not required (54). This demonstrates the importance of H for vaccine attenuation and highlights the relative contributions of N glycosylation and primary sequence differences between vaccine and wild-type strain H proteins to virulence.…”

“…While the N-glycan-deficient H proteins are otherwise identical to H 5804P , the lack of the N-glycan at N149 may also play a role in altering the interaction between F and H. This N-glycan is likely to be in close proximity to F (23), and its absence may destabilize the F-H complex. The virus bearing the vaccine H protein had a strongly reduced capacity to inhibit lymphocyte proliferation compared to the N-glycan-deficient viruses, which suggests that differences in contact inhibition are contributing factors (38,54,55).…”

Respiratory Syncytial Virus Fusion Protein Mediates Inhibition of Mitogen-Induced T-Cell Proliferation by Contact

“…Another requirement for MeV contact inhibition is proteolytic cleavage of the fusion protein, whereas membrane fusion is not necessary (47). From these data it appears that only the fusion-competent MeV F/H complex may acquire a structure effective in signaling inhibition.…”

Human Langerhans cells capture measles virus through Langerin and present viral antigens to CD4+ T cells but are incapable of cross‐presentation

“…The following antibodies were used: anti-CD150 (A12, Abd Serotec; 5C6 [44]), anti-Langerin (10E2, IgG1 [10]; DCGM4, Beckman Coulter; polyclonal goat, R&D Systems), anti-MV-F (A5047 [45] …”