Psychological stress impairs the local CD8+ T cell response to mucosal HSV-1 infection and allows for increased pathogenicity via a glucocorticoid receptor-mediated mechanism

Abstract

Psychological stress and its associated increases in corticosterone are generally immunosuppressive and contribute to increased herpes simplex virus (HSV)-associated pathogenicity. However, the impact of stress on local control of the initial mucosal-based HSV infection has not been elucidated, nor have the ramifications of such failures of the immune response in terms of viral spread. To address these gaps in knowledge, the studies described herein sought to determine how psychological stress and associated increases in corticosterone may increase susceptibility to HSV encephalitis by allowing for increased viral titers at the site of initial infection. We have shown that in mice intranasally infected with HSV-1, a cell-mediated immune response occurs in the nasopharyngeal-associated lymphoid tissue (NALT), mediastinal lymph nodes (MLN), and superficial cervical lymph nodes (CLN). However, psychological stress induced by restraint decreased the number of lymphocytes in these tissues in HSV-infected mice. Surprisingly, the effects of this restraint stress on HSV-specific CTL function varied by immune tissue. Increased viral titers were found in the nasal cavity of stressed mice, an observation which correlated with an increased CD8+ cell response in the CLN. These findings led us to extend our studies to also determine the ramifications of decreased numbers of locally derived lymphocytes on viral titers following infection. Using an approach in which the NALT was surgically removed prior to infection, we confirmed that decreased numbers of NALT-derived lymphocytes at the time of infection allows for increased viral replication. We conclude that the increased viral titers observed in mice experiencing psychological stress are the consequence of a glucocorticoid-mediated reduction in the numbers of lymphocytes responsible for resolving the initial infection.

Figure 1

Effect of stress on CD4⁺ and CD8⁺ T lymphocyte populations within the NALT (A), MLN (B), and CLN (C). Mice were subjected to food-and-water deprivation (FWD; black bars) or restraint stress (STRESS; white bars) for six consecutive sessions. Immediately following the sixth session, mice were euthanized and lymphocytes from the NALT, MLN, and CLN were isolated and quantified as described in the Methods. The numbers of NALT-derived lymphocytes for restraint mice are expressed as a percentage of the FWD control mice, since the numbers of NALT-derived lymphocytes varied among experiments. n = 5–9 for all groups. ^* Significant difference (p < 0.05) as compared to FWD control mice.

Figure 2

Effect of exogenous corticosterone on CD4⁺ and CD8⁺ T lymphocyte populations within the NALT (A), MLN (B), and CLN (C). Mice were provided drinking water containing either vehicle (VEH; black bars) or 100 µg/mL corticosterone (CORT; white bars) for six consecutive days. On the sixth day, mice were euthanized and lymphocytes from the NALT, MLN, and CLN were isolated and quantified as described in the Methods. The numbers of NALT-derived lymphocytes for CORT mice are expressed as a percentage of control (VEH) mice, since the numbers of NALT-derived lymphocytes varied among experiments. n = 4–7 for all groups. ^* Significant difference (p < 0.01) as compared to VEH control mice.

Figure 3

Effect of stress on total and gB_498–595-specific CD8⁺ T lymphocytes. Mice were subjected to restraint stress (STRESS) or food-and-water deprivation (FWD) and infected with 1 × 10⁷ PFU HSV-1 as described in the Methods. Seven days post-infection, mice were euthanized and lymphocytes from the NALT (A), MLN (B), and CLN (C) were collected and quantified for CD8⁺ expression (gray bars), and assessed for gB_498–505-specificity (white bars) using a gB_498–505/H-2K^b tetramer. The percentage of CD8⁺ T cells with receptors specific for the gB_498–505 epitope is illustrated in panel D. n = at least 5 for all groups. ^* Significant difference (p < 0.05) in total CD8⁺ cell numbers between the indicated groups. ^# Significant difference (p < 0.05) in gB_498–505-specific T cells between the indicated groups.

Figure 4

Effect of stress and exogenous corticosterone on CD8⁺ T cell function within the NALT, MLN, and CLN. Mice were subjected to restraint stress (STRESS) or provided with corticosterone (CORT) beginning one day prior to infection with 1 × 10⁷ PFU HSV-1. Seven days post-infection, the CD8⁺ cells within the NALT (A, B), MLN (C, D), or CLN (E, F) were assessed for degranulation (A, C, E) or interferon-γ production (B, D, F) in response to stimulation with gB_498–505 peptide. Results were normalized within individual experiments to the number of functioning cells in HSV-1 infected, food-and-water-deprived mice. n = at least 4 for all groups. ^* Significant difference (p < 0.05) as compared to infected, FWD control mice.

Figure 5

Effect of stress and exogenous corticosterone on the control of intranasal HSV-1 infection. Mice were intranasally infected with 1 × 10⁷ PFU HSV-1. Restraint stress (STRESS) or providing corticosterone in the drinking water (CORT) began one day prior to infection; control mice were deprived of food and water (FWD) in lieu of restraint. Five days post-infection, mice were euthanized and nasal washes were collected as described in the Methods. Virus within the washes was titered and is expressed in terms of log₁₀ PFU/nasal cavity. n = 6–14 for all groups. ^* Significant difference between the indicated groups.

Figure 6

Effect of surgical NALT removal on HSV titers following intranasal infection. Mice underwent surgery to remove the NALT (SURGERY) or were simply administered anesthesia and analgesia (CONTROL). Three weeks after surgery, all mice were infected with 1 × 10⁷ PFU HSV-1. Five days post-infection, the NALT was examined to confirm the surgical reduction in NALT-derived lymphocytes (A), and nasal washes were collected. The levels of infectious HSV within the washes were determined and are expressed in terms of PFU/mL (B). n = 2, 3 (A) and 7, 6 (B) for control and surgery groups, respectively. ^* Significant difference as compared to control mice.