Manoj Thapa

Susceptibility of CCR5-Deficient Mice to Genital Herpes Simplex Virus Type 2 Is Linked to NK Cell Mobilization

ABSTRACT Following genital herpes simplex virus type 2 (HSV-2) exposure, NK cells and T cells are mobilized to sites of infection to control viral replication and spread. The present investigation sought to determine the role of the chemokine receptor CCR5 in this process. Mice deficient in CCR5 (CCR5−/−) displayed a significant reduction in cumulative survival following infection in comparison to wild-type, HSV-2-infected controls. Associated with decreased resistance to viral infection, CCR5−/− mice yielded significantly more virus and expressed higher levels of tumor necrosis factor alpha, CXCL1, CCL2, CCL3, and CCL5 in the vagina, spinal cord, and/or brain stem than did wild-type mice. Whereas there was no difference in absolute number of leukocytes (CD45high), CD4 T cells, or CD8 T cells residing in the draining lymph nodes, spleen, spinal cord, or brain stem comparing HSV-2-infected wild-type to CCR5−/− mice prior to or after infection, there were significantly more NK cells (NK1.1+ CD3−) residing in the brain stem and spleen of infected wild-type mice. Functionally, NK activity from cells isolated from the brain stem of HSV-2-infected wild-type mice was greater than that from HSV-2-infected CCR5−/− mice. In addition, antibody-mediated depletion of NK cells resulted in an increase in HSV-2 levels in the vaginal, spinal cord, and brain stem tissue of wild-type but not CCR5−/− mice. Collectively, the absence of CCR5 expression significantly impacts the ability of the host to control genital HSV-2 infection, inflammation, and spread associated with a specific reduction in NK cell expansion, infiltration, and activity in the nervous system.

CXCL9 and CXCL10 Expression Are Critical for Control of Genital Herpes Simplex Virus Type 2 Infection through Mobilization of HSV-Specific CTL and NK Cells to the Nervous System

CXCL9 and CXCL10 mediate the recruitment of T lymphocytes and NK cells known to be important in viral surveillance. The relevance of CXCL10 in comparison to CXCL9 in response to genital HSV-2 infection was determined using mice deficient in CXCL9 (CXCL9−/−) and deficient in CXCL10 (CXCL10−/−) along with wild-type (WT) C57BL/6 mice. An increased sensitivity to infection was found in CXCL10−/− mice in comparison to CXCL9−/− or WT mice as determined by detection of HSV-2 in the CNS at day 3 postinfection. However, by day 7 postinfection both CXCL9−/− and CXCL10−/− mice possessed significantly higher viral titers in the CNS in comparison to WT mice consistent with mortality (18–35%) of these mice within the first 7 days after infection. Even though CXCL9−/− and CXCL10−/− mice expressed elevated levels of CCL2, CCL3, CCL5, and CXCL1 in the spinal cord in comparison to WT mice, there was a reduction in NK cell and virus-specific CD8+ T cell mobilization to this tissue, suggesting CXCL9 and CXCL10 are critical for recruitment of these effector cells to the spinal cord following genital HSV-2 infection. Moreover, leukocytes from the spinal cord but not from draining lymph nodes or spleens of infected CXCL9−/− or CXCL10−/− mice displayed reduced CTL activity in comparison to effector cells from WT mice. Thus, the absence of CXCL9 or CXCL10 expression significantly alters the ability of the host to control genital HSV-2 infection through the mobilization of effector cells to sites of infection.

CXCR3 Deficiency Increases Susceptibility to Genital Herpes Simplex Virus Type 2 Infection: Uncoupling of CD8+ T-Cell Effector Function but Not Migration

ABSTRACT CXCR3 is a G-protein-coupled receptor preferentially expressed by activated T cells, NK cells, and dendritic cells. Signaling through gamma interferon-regulated chemokines CXCL9, CXCL10, CXCL11, and CXCR3 plays a critical role in the immune response of many viral pathogens. However, the relevance of CXCR3 for optimal T-cell activation and the induction of regulatory transcription factors (i.e., T-bet and eomesodermin) relative to host immune defense against genital herpes simplex virus type 2 (HSV-2) infection have been poorly defined. In this study, we evaluated the requirement of CXCR3 expression during genital HSV-2 infection using mice deficient in CXCR3 (CXCR3−/−) along with wild-type (WT) controls, assessing the resistance of mice to viral infection and focusing on the cytokine/chemokine response, phenotypic analysis of recruited leukocytes, and functional analysis of CD8+ T cells. CXCR3−/− mice showed a heightened sensitivity to infection compared to WT animals in terms of the viral burden in infected tissues as well as elevated mortality. The poor response of CXCR3−/− mice to viral infection was associated with reduced cytotoxic T-lymphocyte activity through the impairment of T-bet, perforin, and granzyme B expression by CD8+ T cells. Corresponding with the defective cytolytic activity, a reduction in recruitment of plasmacytoid dendritic cells and CD80 expression in CD11c+ dendritic cells in the draining lymph nodes of CXCR3−/− mice were detected. Collectively, the results provide a new perspective to CXCR3 signaling for the appropriate activation of CD8+ T cells required for host defense against genital HSV-2 infection.

Loss of Mandibular Lymph Node Integrity Is Associated with an Increase in Sensitivity to HSV-1 Infection in CD118-Deficient Mice

Type I IFNs are potent antiviral cytokines that contribute to the development of the adaptive immune response. To determine the role of type I IFNs in this process in an infectious disease model, mice deficient in the type I IFN receptor (CD118−/−) were ocularly infected with HSV-1 and surveyed at times post infection in the nervous system and lymph node for virus and the host immune response. Virus titers were elevated in the trigeminal ganglia and brain stem with virus disseminating rapidly to the draining lymph node of CD118−/− mice. T cell and plasmacytoid dendritic cell infiltration into the brain stem was reduced in CD118−/− mice following infection, which correlated with a reduction in CXCL10 but not CXCL9 expression. In contrast, CXCL1 and CCL2 levels were up-regulated in the brainstem of CD118−/− mice associated with an increase in F4/80+ macrophages. By day 5 post infection, there was a significant loss in T, NK, and plasmacytoid dendritic cell numbers in the draining lymph nodes associated with an increase in apoptotic/necrotic T cells and an appreciable lack of HSV-specific CD8+ T cells. The adoptive transfer of HSV-specific TCR transgenic CD8+ T cells into CD118−/− mice at the time of infection modestly reduced viral titers in the nervous system suggesting in addition to the generation of HSV-specific CD8+ T cells, other type I IFN-activated pathways are instrumental in controlling acute infection.

Chemokines and Chemokine Receptors Critical to Host Resistance following Genital Herpes Simplex Virus Type 2 (HSV-2) Infection

HSV-2 is a highly successful human pathogen with a remarkable ability to elude immune detection or counter the innate and adaptive immune response through the production of viral-encoded proteins. In response to infection, resident cells secrete soluble factors including chemokines that mobilize and guide leukocytes including T and NK cells, neutrophils, and monocytes to sites of infection. While there is built-in redundancy within the system, chemokines signal through specific membrane-bound receptors that act as antennae detailing a chemical pathway that will provide a means to locate and eliminate the viral insult. Within the central nervous system (CNS), the temporal and spatial expression of chemokines relative to leukocyte mobilization in response to HSV-2 infection has not been elucidated. This paper will review some of the chemokine/chemokine receptor candidates that appear critical to the host in viral resistance and clearance from the CNS and peripheral tissue using murine models of genital HSV-2 infection.

Herpes Simplex Virus Type 2-Induced Mortality following Genital Infection Is Blocked by Anti-Tumor Necrosis Factor Alpha Antibody in CXCL10-Deficient Mice

ABSTRACT The role of tumor necrosis factor alpha (TNF-α) was evaluated for CXCL10-deficient (CXCL10−/−) mice which succumbed to genital herpes simplex virus type 2 (HSV-2) infection and possessed elevated levels of virus and TNF-α but not other cytokines in the central nervous system (CNS) and vaginal tissue within the first 7 days following virus exposure. Anti-TNF-α but not control antibody treatment offsets the elevated mortality rate of CXCL10−/− mice, despite increased CNS viral titers. In addition, TNF-α neutralization suppressed recruitment of leukocyte subpopulations into the CNS, which is associated with reduced CCL2 and CXCL9 expression. Collectively, the results implicate TNF-α as the principal mediator of mortality in response to genital HSV-2 infection.

CXCL10 expressing hematopoietic-derived cells are requisite in defense against HSV-1 infection in the nervous system of CXCL10 deficient mice.

The chemokine CXCL10 is crucial for the control of viral replication through the regulation of mobilization of antigen-specific T cells to sites of infection. CXCL10 is highly expressed both at sites of inflammation as well as constitutively within lymphoid organs by both bone marrow (BM)-derived and non-BM-derived cells. However, the relative immunologic importance of CXCL10 expressed by these divergent sources relative to HSV-1 infection is unknown. Using mouse chimeras reconstituted with either wild type or CXCL10 deficient mouse BM, we show BM-derived, radiation-sensitive cells from wild type mice were solely responsible for resistance to HSV-1 in the trigeminal ganglia and brain stem. The resistance was not reflected by a deficiency in the recruitment of effector cells to sites of inflammation or expression of chemokines or IFN-gamma and likely results from additional, yet-to-be-determined factors emanating from wild type, BM-derived cells.