At 70C80% confluency cells were transfected with 15 ug or 1ug (Fig 8) of the indicated plasmid using XtremeGENE HP reagent (Sigma Aldrich) in OPTI-MEM (Thermofisher) in DMEM supplemented with 5% FBS and L-glutamine. lines was verified by co-culturing these cells with T cell hybridomas specific for each peptide. T cell activation was measured by proxy of -galactosidase conversion of MUG substrate.(TIF) ppat.1008685.s004.tif (203K) GUID:?1EAE6540-8994-4F12-8C55-ACA14F167956 S1 Data: Excel spreadsheet containing, in individual sheets, the underlying numerical data and statistical analysis for Figure panels 1a, 1b, 2b, 2c, 2d, 3a, 3b, 3c, 3d, 4a-f, 6a, 6b, 6c, 7, 8b, 8d, SF1, SF2, SF4. (XLSX) ppat.1008685.s005.xlsx (65K) GUID:?87C0A33A-C821-4010-99CC-F4696B7BED87 Data Availability StatementAll relevant data are within the manuscript and its Supporting Information files. Abstract Smallpox and monkeypox pose severe threats to human health. Other orthopoxviruses are comparably virulent in their natural hosts, including ectromelia, the cause of mousepox. Disease severity is linked to an array of immunomodulatory proteins including the B22 family, which has homologs in all pathogenic orthopoxviruses but not attenuated vaccine strains. We demonstrate that this ectromelia B22 member, C15, is necessary and sufficient for selective inhibition of CD4+ but not CD8+ T cell activation by immunogenic peptide and superantigen. Inhibition Ademetionine is usually achieved not by down-regulation of surface MHC- II or co-stimulatory protein surface expression but rather by interference with antigen presentation. The appreciable outcome is interference with CD4+ T cell synapse formation as determined by imaging studies and lipid raft disruption. Consequently, CD4+ T cell activating stimulus shifts to uninfected antigen-presenting cells that have received antigen from infected cells. This work provides insight into the immunomodulatory strategies of orthopoxviruses by elucidating a mechanism for specific targeting of CD4+ T cell activation, reflecting the importance of this cell type in control of the computer virus. Author summary Orthopoxviruses pose considerable threats to their hosts by producing a battery of proteins that disable the immune system at many levels through mechanisms that remain poorly understood. An essential part of most immune responses is the activation of CD4+ T cells by antigen-presenting cells through formation of a supramolecular structure termed the immunological synapse. We show here that this C15 protein of ectromelia, the cause of mousepox, inhibits CD4+ T cell activation through a novel immunoevasion mechanism that results in disruption of synapse formation. As many poxviruses encode C15 homologs, these studies could provide insights into the virulence of other family members including monkeypox and smallpox, both of Ademetionine great concern to human populations. Introduction CD4+ T cells are a crucial adaptive immune cell type with functions in B cell and CD8+ T cell help, inflammatory cytokine secretion and, in some cases, direct cytolytic function. The crucial initiating events for CD4+ T cell activation are Major Histocompatibility Complex class II (MHCII) presentation of pathogen derived peptides (epitopes) in combination with co-stimulatory signals through CD28 [1]. As CD4+ T cells play important functions in clearing many viral infections, several mechanisms by which viruses inhibit MHCII antigen processing and presentation have been described [2]. For example, most steps of the MHCII maturation process are targeted, from GLP-1 (7-37) Acetate inhibition of the grasp transcription factor CIITA [3C8] to interference with complex formation and trafficking [9C11], as well as forced degradation of mature MHCII molecules [12, 13]. In addition, Hepatitis C Computer virus inhibits Ademetionine the function of endosomal proteases required for generating some MHCII binding peptides [14]. Furthermore, Epstein-Barr computer virus (EBV) utilizes a soluble factor to block MHCII engagement with the T cell receptor via steric hindrance [15, 16]. Of note, though discrete mechanisms of inhibition have been described, there are relatively few examples of CD4+ T cell inhibition in the literature compared to the many of viral inhibition of MHCI presentation to CD8+ T cells, perhaps reflecting historical inattention to the role of CD4+ T cells in viral clearance. Another possible explanation for the dearth of inquiries into viral targeting of CD4+ T cells is the prevailing view of the requirements for MHCII processing of antigen. The classical view of MHCII presentation begins with internalization of extracellular material by a professional antigen-presenting cell (APC), followed by processing of antigen within the endocytic network and peptide loading onto nascent MHCII molecules in the late endosomal compartment [1]. However, the presentation of endogenously produced antigen following contamination of the APC via non-canonical processing pathways has been described in many viral systems [17C24]. Indeed, we.