CD4 T Cell Epitope Specificity and Cytokine Potential Are Preserved as Cells Transition from the Lung Vasculature to Lung Tissue following Influenza Virus Infection

Abstract

Pulmonary CD4 T cells are critical in respiratory virus control, both by delivering direct effector function and through coordinating responses of other immune cells. Recent studies have shown that following influenza virus infection, virus-specific CD4 T cells are partitioned between pulmonary vasculature and lung tissue. However, very little is known about the peptide specificity or functional differences of CD4 T cells within these two compartments. Using a mouse model of influenza virus infection in conjunction with intravascular labeling , the cell surface phenotype, epitope specificity, and functional potential of the endogenous polyclonal CD4 T cell response was examined by tracking nine independent CD4 T cell epitope specificities. These studies revealed that tissue-localized CD4 cells were globally distinct from vascular cells in expression of markers associated with transendothelial migration, residency, and micropositioning. Despite these differences, there was little evidence for remodeling of the viral epitope specificity or cytokine potential as cells transition from vasculature to the highly inflamed lung tissue. Our studies also distinguished cells in the pulmonary vasculature from peripheral circulating CD4 T cells, providing support for the concept that the pulmonary vasculature does not simply reflect circulating cells that are trapped within the narrow confines of capillary vessels but rather is enriched in transitional cells primed in the draining lymph node that have specialized potential to enter the lung tissue. CD4 T cells convey a multitude of functions in immunity to influenza, including those delivered in the lymph node and others conveyed by CD4 T cells that leave the lymph node, enter the blood, and extravasate into the lung tissue. Here, we show that the transition of recently primed CD4 cells detected in the lung vasculature undergo profound changes in expression of markers associated with tissue localization as they establish residence in the lung. However, this transition does not edit CD4 T cell epitope specificity or the cytokine potential of the CD4 T cells. Thus, CD4 T cells that enter the infected lung can convey diverse functions and have a sufficiently broad viral antigen specificity to detect the complex array of infected cells within the infected tissue, offering the potential for more effective protective function.

Memory CD4 T cell-derived IL-2 synergizes with viral infection to exacerbate lung inflammation

“…Although we observed similar impacts using TcR transgenic and polyclonal CD4 T cells, a comprehensive understanding of how and when IL-2 produced by CD4 T cell populations impacts infection requires further study. For example, CD4 T cells with different TcR specificities have been shown to produce different amounts of IL-2 upon restimulation with cognate IAV peptides [59], and both higher doses of antigen and higher avidity T cell responses lead to greater IL-2 production [60]. These findings indicate that responses against certain antigens may be more or less impacted by the mechanisms described here.…”

Peptide Epitope Hot Spots of CD4 T Cell Recognition Within Influenza Hemagglutinin During the Primary Response to Infection

“…These studies, as well as our unpublished data with many inbred strains of mice, suggest that the major factor determining CD4 T cell epitope specificity and abundance after influenza infection is the MHC class II molecules expressed in the host. All strains of mice used in the current study elicited robust CD4 T cell responses to other viral proteins after influenza infection, including those specific for M1, NA, and NP ( [22,34,[36][37][38][39][40]43], as shown in Figure 1).…”

“…IL-2 producing CD4 T cells were used to quantify reactivity to influenza epitopes from spleen because in some strains of mice, this is the dominant cytokine expressed particularly in the spleen ( [41] and data not shown). In addition, in contrast to cells localized to the lung, that are enriched for IFN-γ [36,37], IL-2 is reliably expressed by CD4 T cells elicited by infection that localize to secondary lymphoid tissue [34]. Use of peptides and splenic CD4 T cells allowed all potential HA epitopes recognized by the host CD4 T cells to be presented by APC and available to recall the primed CD4 T cells.…”

“…Because of our interest in the full potential repertoire of influenza-specific CD4 T cells, our laboratory has used unbiased epitope scanning methods to identify the entire array of peptides recognized by CD4 T cells in the primary response in mice to influenza infection or vaccination. These studies have involved a diverse set of mouse strains, chosen in part to explore the role of MHC (Major Histocompatibility Complex) class II polymorphism in selection of the immunodominance hierarchy [33,34], the relationship between epitope selection in CD4 T cell responses to infection vs. vaccination [35], CD4 T cell epitope selection during homing to the lung after infection [36,37], partitioning of CD4 T cells into follicular helper cells versus effector cell lineages after infection and vaccination [38], and epitope mapping for identification of human CD4 T cell epitopes via HLA-DR transgenic mice [39,40]. Collectively, these studies have revealed a tremendous breadth in the CD4 T cell response to influenza that includes specificities derived from HA, NA, M1, NP, and the polymerase proteins.…”

The Way Forward: Potentiating Protective Immunity to Novel and Pandemic Influenza Through Engagement of Memory CD4 T Cells

“…Using animal models of infection, it is known that intranasal infection generates a robust CD4 T-cell response detectable in both the local draining lymph node and in the respiratory tract [ 58–60 ]. Despite the magnitude of the initial response in the respiratory tract, most antigen-specific CD4 T cells in the lung decay rather quickly, typically within 3–4 weeks [ 59 , 61 ]. However, it is possible that these encounters through infection establish niches of such memory CD4 T cells, either within the respiratory tract or in the periphery [ 62–65 ].…”