Activation, differentiation, and migration of naive virus-specific CD8+ T cells during pulmonary influenza virus infection

Distinct chemokine triggers and in vivo migratory paths of fluorescein dye-labeled T Lymphocytes in acutely simian immunodeficiency virus SIVmac251-infected and uninfected macaques

To define the possible impact of T-lymphocyte trafficking parameters on simian immunodeficiency virus (SIV) pathogenesis, we examined migratory profiles of carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled T lymphocytes in acutely SIVmac251-infected and uninfected macaques within 48 h after autologous transfer. Despite significant upregulation of homeostatic chemokine CCL19/macrophage inflammatory protein 3beta and proinflammatory chemokine CXCL9/monokine induced by gamma interferon in secondary lymphoid tissue in SIV infection, no differences in CFSE+ T-lymphocyte frequencies or cell compartmentalization in lymph nodes were identified between animal groups. By contrast, a higher frequency of CFSE+ T lymphocytes in the small intestine was detected in acute SIV infection. This result correlated with increased numbers of gut CD4 T lymphocytes expressing chemokine receptors CCR9, CCR7, and CXCR3 and high levels of their respective chemokine ligands in the small intestine. The changes in trafficking parameters in SIV-infected macaques occurred concomitantly with acute gut CD4 T-lymphocyte depletion. Here, we present the first in vivo T-lymphocyte trafficking study in SIV infection and a novel approach to delineate T-lymphocyte recruitment into tissues in the nonhuman primate animal model for AIDS. Such studies are likely to provide unique insights into T-lymphocyte sequestration in distinct tissue compartments and possible mechanisms of CD4 T-lymphocyte depletion and immune dysfunction in simian AIDS.

Transient loss of MHC class I tetramer binding after CD8+ T cell activation reflects altered T cell effector function

Engagement of the Ag receptor on naive CD8+ T cells by specific peptide-MHC complex triggers their activation/expansion/differentiation into effector CTL. The frequency of Ag-specific CD8+ T cells can normally be determined by the binding of specific peptide-MHC tetramer complexes to TCR. In this study we demonstrate that, shortly after Ag activation, CD8+ T cells transiently lose the capacity to efficiently bind peptide-MHC tetramer complexes. This transient loss of tetramer binding, which occurs in response to naturally processed viral peptide during infection in vitro and in vivo, is associated with reduced signaling through the TCR and altered/diminished effector activity. This change in tetramer binding/effector response is likewise associated with a change in cell surface TCR organization. These and related results suggest that early during CD8+ T cell activation, there is a temporary alteration in both cell surface Ag receptor display and functional activity that is associated with a transient loss of cognate tetramer binding.

The CD8 memory T cell subsystem: integration of homeostatic signaling during migration

The ability of memory CD8 T cells to patrol non-lymphoid tissues represents an effective method whereby proficient immunosurveillance is achieved. From the analysis of memory CD8 T cell migration in vivo, it is clear that tissue-specific factors control trafficking and residence time within tissues. We propose that at least three pools of memory CD8 T cells exist based on migratory capabilities as dictated by their location in the body. Moreover, we hypothesize that the process of acquisition of homeostatic signals in specific tissues, such as the cytokines IL-7 and IL-15, regulates the mobility of memory T cells.

Understanding presentation of viral antigens to CD8+ T cells in vivo: the key to rational vaccine design

CD8+ T cells play a critical role in antiviral immunity by exerting direct antiviral activity against infected cells. Because of their ability to recognize all types of viral proteins, they offer the promise of providing broad immunity to viruses that evade humoral immunity by varying their surface proteins. Consequently, there is considerable interest in developing vaccines that elicit effective antiviral T(CD8+) responses. Generating optimal vaccines ultimately requires rational design based on detailed knowledge of how T(CD8+) are activated in vivo under natural circumstances. Here we review recent progress obtained largely by in vivo studies in mice to understand the mechanistic basis for activation of naive T(CD8+) in virus infections. These studies point the way to detailed understanding and provide some key information for vaccine development, although much remains to be learned to enable truly rational vaccine design.

Dendritic cells maximize the memory CD8 T cell response to infection

Costimulatory signals from dendritic cells (DCs) are required for naive T cells to respond to antigenic stimulation. To what extent DCs reactivate memory T cells during recall responses is not known. Here, an in vivo depletion system has been used to analyze the role of DCs in reactivating CD8 memory T cells during recall responses to three different microbial infections. We show a profound decrease in the numbers of responding memory CD8 T cells in both lymphoid and nonlymphoid tissues during the recall responses to infection with vesicular stomatitis virus, Listeria monocytogenes (Lm), or influenza virus. These data show that interaction with DCs is a major mechanism driving T cell reactivation in vivo, even during a tissue-specific infection of the respiratory tract.

Frequency, Specificity, and Sites of Expansion of CD8+T Cells during Primary Pulmonary Influenza Virus Infection

We have used intracellular cytokine staining and MHC class I tetramer binding in conjunction with granzyme B protease expression and in vivo BrdU uptake to characterize the primary murine CD8(+) T cell response to pulmonary influenza virus infection. We have observed that the majority (>90%) of the CD8(+) T cell response to the A/Japan/305/57 virus in the lung at the peak of the response (days 9-11) is directed to four epitopes (three dominant and one subdominant). Using induction of granzyme B as a surrogate to identify specific activated CD8(+) T cells, we found that an unexpectedly large fraction ( approximately 70%) of lung-infiltrating CD8(+) T cells expressed granzyme B on day 6 of infection when estimates by MHC tetramer/intracellular cytokine staining yielded substantially lower frequencies ( approximately 30%). In addition, by using intranasal administration of BrdU during infection, we obtained evidence for proliferative expansion of activated CD8(+) T cells in the infected lung early (days 5-7) in the primary response. These results suggest that the frequency and number of specific CTL present in the lung early in infection may be underestimated by standard detection methods, and primary CD8(+) T cell expansion may occur in both secondary lymphoid organs and the infected lung.

Chronic nicotine inhibits inflammation and promotes influenza infection

Epidemiological data suggest an association between smoking, respiratory infections, and impaired wound healing. Inflammation is critical in the body's defense against pathogens and in the wound-healing process. Although nicotine is used to treat some inflammatory conditions, the mechanism of this action is largely unknown. To determine how nicotine affects inflammation, rats and mice were exposed to nicotine via miniosmotic pumps, and the inflammatory response to turpentine or influenza virus was assessed. Results showed that while nicotine suppressed the migration of leukocytes to the inflammation/infection site, it increased the influenza titer in the lung. The decreased inflammation correlated with lower chemotaxis/chemokinesis of peripheral blood mononuclear cells (PBMC) toward formyl-methionyl-leucyl-phenylalanine and monocyte chemoattractant protein-1 without affecting the density of their respective receptors. However, nicotine suppressed the chemokine-induced Ca(2+) response in PBMC, indicating impaired chemokine signaling. Thus, because nicotine suppresses leukocyte migration, it might contribute to the delayed wound healing and increased incidence of respiratory infections among smokers.