Aaruni Khanolkar

Maintenance, Loss, and Resurgence of T Cell Responses During Acute, Protracted, and Chronic Viral Infections

The acute phase of many viral infections is associated with the induction of a pronounced CD8 T cell response which plays a principle role in clearing the infection. By contrast, certain infections are not as readily controlled. In this study, we have used the well-defined system of lymphocytic choriomeningitis virus (LCMV) infection of mice to determine quantitative and qualitative changes in virus-specific CD8 T cell responses that rapidly resolve acute infections, more slowly control protracted infections, or fail to clear chronic infections. Acute LCMV infection elicits potent, functional, multi-epitope-specific CD8 T cell responses. Virus-specific CD8 T cells also expand, albeit to a lesser extent, during protracted LCMV infection. Under these conditions, there is a progressive diminution in the capacity to produce IL-2, TNF-α, and IFN-γ. Changes in cytotoxic activities are also detectable but differ depending upon the specificity of the responding cells. As the infection is slowly resolved, a resurgence of cytokine production by virus-specific CD8 T cells is observed. CD4-deficient mice cannot control infection with certain strains of LCMV, but do mount multi-epitope-specific CD8 T cell responses that also lose effector capabilities; however, they are not maintained indefinitely in an unresponsive state as these cells become deleted over time. Overall, our findings suggest that constant high viral loads result in the progressive diminution of T cell effector functions and subsequent physical loss of the responding cells, whereas if the viral load is brought under control a partial restoration of CD8 T cell functions can occur.

CD4 T Cell-Dependent CD8 T Cell Maturation

We have investigated the contribution of CD4 T cells to the optimal priming of functionally robust memory CD8 T cell subsets. Intranasal infection of CD4 T cell-deficient (CD4−/−) mice with lymphocytic choriomeningitis virus resulted in the elaboration of virus-specific CD8 T cell responses that cleared the infection. However, by comparison with normal mice, the virus-specific CD8 T cells in CD4−/− mice were quantitatively and qualitatively different. In normal mice, lymphocytic choriomeningitis virus-specific memory CD8 T cells are CD44high, many are CD122high, and a majority of these cells regain expression of CD62L overtime. These cells produce IFN-γ and TNF-α, and a subset also produces IL-2. In the absence of CD4 T cell help, a distinct subset of memory CD8 T cells develops that remains CD62Llow up to 1 year after infection and exhibits a CD44intCD122low phenotype. These cells are qualitatively different from their counterparts in normal hosts, as their capacity to produce TNF-α and IL-2 is diminished. In addition, although CD4-independent CD8 T cells can contain the infection following secondary viral challenge, their ability to expand is impaired. These findings suggest that CD4 T cell responses not only contribute to the optimal priming of CD8 T cells in chronically infected hosts, but are also critical for the phenotypic and functional maturation of CD8 T cell responses to Ags that are more rapidly cleared. Moreover, these data imply that the development of CD62Lhigh central memory CD8 T cells is arrested in the absence of CD4 T cell help.

T cell responses to viral infections: Lessons from lymphocytic choriomeningitis virus

The elaboration of a successful immune response is critical for the clearance of viral infections. CD8 T cells can directly kill virus-infected cells and also produce cytokines that modulate virus replication. Thus, the failure to induce or sustain these responses can profoundly impact the outcome of infections. Lymphocytic choriomeningitis virus (LCMV) infection of mice has proven to be one of the most informative experimental systems for examining antiviral T cell responses. In recent years, the application of newly developed approaches to analyze these responses has revealed that acute infections induce remarkably high levels of antiviral T cells. By contrast, protracted or chronic infections are associated with both the functional impairment and deletion of virus-specific CD8 T cells. This article discusses some of our findings using LCMV infection of mice as well as their relevance to other infections of animals and humans.

Listeriolysin O-Deficient Listeria monocytogenes as a Vaccine Delivery Vehicle: Antigen-Specific CD8 T Cell Priming and Protective Immunity

Strains of Listeria monocytogenes (LM) that are deficient in the virulence factor listeriolysin O (LLO) are highly attenuated and are thought not to elicit protective immunity. This failure has been attributed to the inability of the bacterium to enter the host cell cytosol and access MHC class I Ag processing machinery. We reexamined this issue using recombinant strains of LM that are deficient in LLO but express an additional CD8 T cell epitope derived from lymphocytic choriomeningitis virus. After infection with LLO-deficient strains, we find sizable priming of epitope-specific CD8 T cells and the development of a functional memory cell population. Mice primed with the LLO-deficient LM strain are equally resistant against high-dose challenge with virulent LM as mice primed with wild-type virulent bacteria and also resist heterologous challenge with lymphocytic choriomeningitis virus. Interestingly, priming with a low dose of LLO-deficient LM, which occurred in environment of reduced inflammation (IFN-γ), allowed rapid amplification of Ag-specific CD8 T cells by booster immunization, despite an undetectable primary response. We conclude that the generation of protective immunity by LLO-deficient strains of LM does in fact occur and that this highly attenuated LM strain may be a useful platform for vaccine delivery.

Toll-Like Receptor 4 Deficiency Increases Disease and Mortality after Mouse Hepatitis Virus Type 1 Infection of Susceptible C3H Mice

ABSTRACT Severe acute respiratory syndrome (SARS) is characterized by substantial acute pulmonary inflammation with a high mortality rate. Despite the identification of SARS coronavirus (SARS-CoV) as the etiologic agent of SARS, a thorough understanding of the underlying disease pathogenesis has been hampered by the lack of a suitable animal model that recapitulates the human disease. Intranasal (i.n.) infection of A/J mice with the CoV mouse hepatitis virus strain 1 (MHV-1) induces an acute respiratory disease with a high lethality rate that shares several pathological similarities with SARS-CoV infection in humans. In this study, we examined virus replication and the character of pulmonary inflammation induced by MHV-1 infection in susceptible (A/J, C3H/HeJ, and BALB/c) and resistant (C57BL/6) strains of mice. Virus replication and distribution did not correlate with the relative susceptibilities of A/J, BALB/c, C3H/HeJ, and C57BL/6 mice. In order to further define the role of the host genetic background in influencing susceptibility to MHV-1-induced disease, we examined 14 different inbred mouse strains. BALB.B and BALB/c mice exhibited MHV-1-induced weight loss, whereas all other strains of H-2b and H-2d mice did not show any signs of disease following MHV-1 infection. H-2k mice demonstrated moderate susceptibility, with C3H/HeJ mice exhibiting the most severe disease. C3H/HeJ mice harbor a natural mutation in the gene that encodes Toll-like receptor 4 (TLR4) that disrupts TLR4 signaling. C3H/HeJ mice exhibit enhanced morbidity and mortality following i.n. MHV-1 infection compared to wild-type C3H/HeN mice. Our results indicate that TLR4 plays an important role in respiratory CoV pathogenesis.

Chronic granulomatous disease: A large, single-center US experience

Background: Chronic granulomatous disease (CGD) is an uncommon primary immunodeficiency that can be inherited in an X-linked (XL) or an autosomal recessive (AR) manner. We reviewed our large, single-center US experience with CGD. Methods: We reviewed 27 patients at Ann & Robert H. Lurie Children’s Hospital of Chicago from March 1985 to November 2013. Fisher exact test was used to compare differences in categorical variables, and Student t test was used to compare means for continuous variables. Serious infections were defined as those requiring intravenous antibiotics or hospitalization. Results: There were 23 males and 4 females; 19 were XL and 8 were AR. The average age at diagnosis was 3.0 years; 2.1 years for XL and 5.3 years for AR inheritance (P = 0.02). There were 128 serious infections. The most frequent infectious agents were Staphylococcus aureus (n = 13), Serratia (n = 11), Klebsiella (n = 7), Aspergillus (n = 6) and Burkholderia (n = 4). The most common serious infections were pneumonia (n = 38), abscess (n = 32) and lymphadenitis (n = 29). Thirteen patients had granulomatous complications. Five patients were below the 5th percentile for height and 4 were below the 5th percentile for weight. Average length of follow-up after diagnosis was 10.1 years. Twenty-four patients were compliant and maintained on interferon-&ggr;, trimethoprim-sulfamethoxazole and an azole. The serious infection rate was 0.62 per patient-year. Twenty-three patients are alive (1 was lost to follow-up). Conclusions: We present a large, single-center US experience with CGD. Twenty-three of 27 patients are alive after 3276 patient-months of follow-up (1 has been lost to follow-up), and our serious infection rate was 0.62 per patient-year.

Protective and Pathologic Roles of the Immune Response to Mouse Hepatitis Virus Type 1: Implications for Severe Acute Respiratory Syndrome

ABSTRACT Intranasal mouse hepatitis virus type 1 (MHV-1) infection of mice induces lung pathology similar to that observed in severe acute respiratory syndrome (SARS) patients. However, the severity of MHV-1-induced pulmonary disease varies among mouse strains, and it has been suggested that differences in the host immune response might account for this variation. It has also been suggested that immunopathology may represent an important clinical feature of SARS. Little is known about the host immune response to MHV-1 and how it might contribute to some of the pathological changes detected in infected mice. In this study we show that an intact type I interferon system and the adaptive immune responses are required for controlling MHV-1 replication and preventing morbidity and mortality in resistant C57BL/6J mice after infection. The NK cell response also helps minimize the severity of illness following MHV-1 infection of C57BL/6J mice. In A/J and C3H/HeJ mice, which are highly susceptible to MHV-1-induced disease, we demonstrate that both CD4 and CD8 T cells contribute to morbidity during primary infection, and memory responses can enhance morbidity and mortality during subsequent reexposure to MHV-1. However, morbidity in A/J and C3H/HeJ mice can be minimized by treating them with immune serum prior to MHV-1 infection. Overall, our findings highlight the role of the host immune response in contributing to the pathogenesis of coronavirus-induced respiratory disease.

Antigen Experience Shapes Phenotype and Function of Memory Th1 Cells

Primary and secondary (boosted) memory CD8 T cells exhibit differences in gene expression, phenotype and function. The impact of repeated antigen stimulations on memory CD4 T cells is largely unknown. To address this issue, we utilized LCMV and Listeria monocytogenes infection of mice to characterize primary and secondary antigen (Ag)-specific Th1 CD4 T cell responses. Ag-specific primary memory CD4 T cells display a CD62LloCCR7hi CD27hi CD127hi phenotype and are polyfunctional (most produce IFNγ, TNFα and IL-2). Following homologous prime-boost immunization we observed pathogen-specific differences in the rate of CD62L and CCR7 upregulation on memory CD4 T cells as well as in IL-2+IFNγco-production by secondary effectors. Phenotypic and functional plasticity of memory Th1 cells was observed following heterologous prime-boost immunization, wherein secondary memory CD4 T cells acquired phenotypic and functional characteristics dictated by the boosting agent rather than the primary immunizing agent. Our data also demonstrate that secondary memory Th1 cells accelerated neutralizing Ab formation in response to LCMV infection, suggesting enhanced capacity of this population to provide quality help for antibody production. Collectively these data have important implications for prime-boost vaccination strategies that seek to enhance protective immune responses mediated by Th1 CD4 T cell responses.

T Cell Epitope Specificity and Pathogenesis of Mouse Hepatitis Virus-1–Induced Disease in Susceptible and Resistant Hosts

Intranasal mouse hepatitis virus-1 (MHV-1) infection of susceptible mouse strains mimics some important pathologic features observed in the lungs of severe acute respiratory syndrome (SARS)-coronavirus–infected humans. The pathogenesis of SARS remains poorly understood, although increasing evidence suggests that immunopathology could play an important role. We previously reported that the adaptive immune response plays an important protective role in MHV-1–infected resistant B6 mice and that both CD4 and CD8 T cells play a significant role in the development of morbidity and lung pathology following intranasal MHV-1 infection of susceptible C3H/HeJ and A/J mice. In this study, we have identified novel CD4 and CD8 epitopes in MHV-1–infected susceptible and resistant strains of mice. Susceptible C3H/HeJ mice mount robust and broad MHV-1–specific CD4 T cell responses, whereas in resistant B6 mice, Ag-specific CD8 T cell responses dominate. We also show that previously immunized susceptible C3H/HeJ mice do not develop any morbidity and are completely protected following a lethal-dose MHV-1 challenge despite mounting only a modest secondary T cell response. Finally, we demonstrate that the resistance displayed by B6 mice is not solely accounted for by the elaboration of a broad and vigorous MHV-1–specific CD8 T cell response, as MHV-1 infection of C3.SW-H2b/SnJ mice, which mount an equally robust CD8 T cell response of the same specificity, is still associated with significant morbidity. Thus, identification of novel CD4 and CD8 T cell epitopes for MHV-1 permitted high-resolution analyses of pulmonary T cell responses in a mouse model of SARS.

Initial results of a novel pre-deposition seeding technique for achieving an ultra-high nucleation density for CVD diamond growth

Abstract The unique thermal properties of diamond, along with the ability to deposit it over large areas, make it an appropriate candidate for electronic packaging and other thermal management applications. In a recent exploration, our group observed defects in diamond films, referred to as “microcavities”. Microcavities are essentially voids in CVD diamond resulting from the growth of randomly-oriented grains. These microcavities present serious challenges to the fabrication of high-density electronic packages when they appear at the surface of the film/substrate. Two approaches for solving the microcavity problem were explored; (1) “planarization by filling” and (2) enhancement of the nucleation density. Results of the first approach have been reported elsewhere. The latter approach, which is the subject of this paper, is based on an electrostatic seeding technique for uniformly depositing nanometer size diamond particles over the entire surface of any material of any shape to serve as nucleation sites for diamond growth. This approach to initiating diamond growth is inexpensive and simple. The resulting films are very dense, and both the number and size of the microcavities are significantly reduced. Details of the seeding technique and resulting diamond films, characterized using SEM, will be discussed.