Programmed Death 1: a key target for the rescue of antigen specific CD4+ T-cell responses during chronic Lymphocytic Choriomeningitis Virus infection

CD4+ T -cell activity, including major histocompatibility class II (MHC II) responses, is vital for proper immune system function including CDS+ T -cell and B cell activation. The identification of antigen specific responses are understudied during chronic Lymphocytic Choriomeningitis virus (LCMV) infection. Therefore, it is pertinent to characterize the functionality and clonal expansion of antigen specific CD4+ T-cell populations to establish a murine model for infection where variables such as viral strain can be manipulated to properly track MHC II restricted CD4+ T cell responses. The expansion of antigen specific CD4+ T cell populations were tracked following the infection of female C57BL/6J mice with LCMV Armstrong (Arm), an acute strain, and LCMV clone 13, a chronic strain. Previously characterized MHC-II l-Ab restricted epitopes, arising from glycoprotein (GP) of the viral proteome, were developed into MHC-11 tetramers. These tetramers were subsequently used to test for the presence of antigen specific CD4+ T -cell populations following exposure to LCMV Arm and clone 13. Fluorescence activated cell sorting (FACS) was used to characterize the expression of a known inhibitory molecule, Programmed Death 1 (PD1), on CD4+ T-cells during acute and chronic infection. Results show that the proliferation and overall degree of CD4+ T -cell expansion are dependent on the specific peptide being presented to CD4+ T -cells by antigen presenting cells (APC's). Following acute infection, CD4+ T-cells expanded on a peptide specific basis, ex vivo, when compared to naive mouse groups. The greatest CD4+ T cell expansion was observed when tracking populations specific for glycoprotein 66 (GP66). Data show PD1 is over expressed on the surface of CD4+ T -cells during clone 13 infection. PDl is also disproportionately over expressed on antigen specific CD4+ T -cells at days 15 and 30 post infection. We here show CD4+ T -cells are dysregulated at the cytokine level following infection with a chronic strain of LCMV, clone 13. Furthermore, this dysfunction coincides with the over expression of a known T -cell lymphocyte inhibitory molecule PDl on the surface of antigen specific CD4+ T -cells. The characterization of PDl expression provides a valuable target for the rescue of CD4+ T cell responses during chronic viral infection in a mammalian model. Keywords: murine, peptide, Lymphocyte dysfunction, T-cell exhaustion, interferon gamma