Destruction of lymphoid organ architecture and hepatitis caused by CD4+ T cells

Fatal Lassa fever in cynomolgus monkeys is associated with systemic viral dissemination and inflammation

The pathogenesis of Lassa fever has not yet been fully deciphered, particularly as concerns the mechanisms determining whether acute infection is controlled or leads to catastrophic illness and death. Using a cynomolgus monkey model of Lassa virus (LASV) infection reproducing the different outcomes of the disease, we performed histological and transcriptomic studies to investigate the dynamics of LASV infection and the immune mechanisms associated with survival or death. Lymphoid organs are an early major reservoir for replicating virus during Lassa fever, with LASV entering through the cortical sinus of draining lymph nodes regardless of disease outcome. However, subsequent viral tropism varies considerably with disease severity, with viral dissemination limited almost entirely to lymphoid organs and immune cells during nonfatal Lassa fever. By contrast, the systemic dissemination of LASV to all organs and diverse cell types, leading to infiltrations with macrophages and neutrophils and an excessive inflammatory response, is associated with a fatal outcome. These results provide new insight into early viral dynamics and the host response to LASV infection according to disease outcome.

Immunotoxic role of organophosphates: An unseen risk escalating SARS-CoV-2 pathogenicity

Consistent gathering of immunotoxic substances on earth is a serious global issue affecting people under pathogenic stress. Organophosphates are among such hazardous compounds that are ubiquitous in nature. They fuel oxidative stress to impair antiviral immune response in living entities. Aside, organophosphates promote cytokine burst and pyroptosis in broncho-alveolar chambers leading to severe respiratory ailments. At present, we witness COVID-19 outbreak caused by SARS-CoV-2. Infection triggers cytokine storm coupled with inflammatory manifestations and pulmonary disorders in patients. Since organophosphate-exposure promotes necroinflammation and respiratory troubles hence during current pandemic situation, additional exposure to such chemicals can exacerbate inflammatory outcome and pulmonary maladies in patients, or pre-exposure to organophosphates might turn-out to be a risk factor for compromised immunity. Fortunately, antioxidants alleviate organophosphate-induced immunosuppression and hence under co-exposure circumstances, dietary intake of antioxidants would be beneficial to boost immunity against SARS-CoV-2 infection.

Pathogenicity of severe fever with thrombocytopenia syndrome virus in mice regulated in type I interferon signaling: Severe fever with thrombocytopenia and type I interferon

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging zoonotic disease, which causes high fever, thrombocytopenia, and death in humans and animals in East Asian countries. The pathogenicity of SFTS virus (SFTSV) remains unclear. We intraperitoneally infected three groups of mice: wild-type (WT), mice treated with blocking anti-type I interferon (IFN)-α receptor antibody (IFNAR Ab), and IFNAR knockout (IFNAR^−/−) mice, with four doses of SFTSV (KH1, 5 × 10⁵ to 5 × 10² FAID₅₀). The WT mice survived all SFTSV infective doses. The IFNAR Ab mice died within 7 days post-infection (dpi) with all doses of SFTSV except that the mice were infected with 5 × 10² FAID₅₀ SFTSV. The IFNAR^−/− mice died after infection with all doses of SFTSV within four dpi. No SFTSV infection caused hyperthermia in any mice, whereas all the dead mice showed hypothermia and weight loss. In the WT mice, SFTSV RNA was detected in the eyes, oral swabs, urine, and feces at 5 dpi. Similar patterns were observed in the IFNAR Ab and IFNAR^−/− mice after 3 dpi, but not in feces. The IFNAR Ab mice showed viral shedding until 7 dpi. The SFTSV RNA loads were higher in organs of the IFNAR^−/− mice compared to the other groups. Histopathologically, coagulation necrosis and mononuclear inflammatory cell infiltration in the liver and white pulp atrophy in the spleen were seen as the main lesions in the IFN signaling lacking mice. Immunohistochemically, SFTSV antigens were mainly detected in the marginal zone of the white pulp of the spleen in all groups of mice, but more viral antigens were observed in the spleen of the IFNAR^−/− mice. Collectively, the IFN signaling-deficient mice were highly susceptible to SFTSV and more viral burden could be demonstrated in various excreta and organs of the mice when IFN signaling was inhibited.

The Janus Face of Follicular T Helper Cells in Chronic Viral Infections

Chronic infections with non-cytopathic viruses constitutively expose virus-specific adaptive immune cells to cognate antigen, requiring their numeric and functional adaptation. Virus-specific CD8 T cells are compromised by various means in their effector functions, collectively termed T cell exhaustion. Alike CD8 T cells, virus-specific CD4 Th1 cell responses are gradually downregulated but instead, follicular T helper (T_FH) cell differentiation and maintenance is strongly promoted during chronic infection. Thereby, the immune system promotes antibody responses, which bear less immune-pathological risk compared to cytotoxic and pro-inflammatory T cell responses. This emphasis on T_FH cells contributes to tolerance of the chronic infection and is pivotal for the continued maturation and adaptation of the antibody response, leading eventually to the emergence of virus-neutralizing antibodies, which possess the potential to control the established chronic infection. However, sustained high levels of T_FH cells can also result in a less stringent B cell selection process in active germinal center reactions, leading to the activation of virus-unspecific B cells, including self-reactive B cells, and to hypergammaglobulinemia. This dispersal of B cell help comes at the expense of a stringently selected virus-specific antibody response, thereby contributing to its delayed maturation. Here, we discuss these opposing facets of T_FH cells in chronic viral infections.

NH36 and F3 Antigen-Primed Dendritic Cells Show Preserved Migrating Capabilities and CCR7 Expression and F3 Is Effective in Immunotherapy of Visceral Leishmaniasis

Physical contact between dendritic cells (DCs) and T cell lymphocytes is necessary to trigger the immune cell response. CCL19 and CCL21 chemokines bind to the CCR7 receptor of mature DCs, and of T cells and regulate DCs migration to the white pulp (wp) of the spleen, where they encounter lymphocytes. In visceral leishmaniasis (VL), cellular immunosuppression is mediated by impaired DC migration due to the decreased chemokine secretion by endothelium and to the reduced DCs CCR7 expression. The Leishmania (L.) donovani nucleoside hydrolase NH36 and its C-terminal domain, the F3 peptide are prominent antigens in the generation of preventive immunity to VL. We assessed whether these vaccines could prevent the migrating defect of DCs by restoring the expression of CCR7 receptors. C57Bl6 mice were vaccinated with NH36 and F3 and challenged with L. (L.) infantum chagasi. The F3 vaccine induced a 100% of survival and a long-lasting immune protection with an earlier CD4+Th1 response, with secretion of higher IFN-γ and TNF-α/IL-10 ratios, and higher frequencies of CD4+ T cells secreting IL-2+, TNF-α+, or IFN-γ+, or a combination of two or the three cytokines (IL-2+TNF-α+IFN-γ+). The CD8+ T cell response was promoted earlier by the NH36-vaccine, and later by the F3-vaccine. Maximal number of F3-primed DCs migrated in vitro in response to CCL19 and showed a high expression of CCR7 receptors (26.06%). Anti-CCR7 antibody treatment inhibited DCs migration in vitro (90%) and increased parasite load in vivo. When transferred into 28-day-infected mice, only 8% of DCs from infected, 59% of DCs from NH36-vaccinated, and 84% of DCs from F3-vaccinated mice migrated to the wp. Consequently, immunotherapy of infected mice with F3-primed DCs only, promoted increases in corporal weight and reductions of spleen and liver parasite loads and relative weights. Our findings indicate that vaccination with F3-vaccine preserves the maturation, migration properties and CCR7 expression of DCs, which are essential processes for the generation of cell-mediated immunity. The F3 vaccine is more potent in reversing the migration defect that occurs in VL and, therefore, more efficient in immunotherapy of VL.

Chronic Brucella Infection Induces Selective and Persistent Interferon Gamma-Dependent Alterations of Marginal Zone Macrophages in the Spleen

The spleen is known as an important filter for blood-borne pathogens that are trapped by specialized macrophages in the marginal zone (MZ): the CD209+ MZ macrophages (MZMs) and the CD169+ marginal metallophilic macrophages (MMMs). Acute systemic infection strongly impacts MZ populations and the location of T and B lymphocytes. This phenomenon has been linked to reduced chemokine secretion by stromal cells. Brucella spp. are the causative agent of brucellosis, a widespread zoonotic disease. Here, we used Brucella melitensis infection as a model to investigate the impact of chronic stealth infection on splenic MZ macrophage populations. During the late phase of Brucella infection, we observed a loss of both MZMs and MMMs, with a durable disappearance of MZMs, leading to a reduction of the ability of the spleen to take up soluble antigens, beads, and unrelated bacteria. This effect appears to be selective as every other lymphoid and myeloid population analyzed increased during infection, which was also observed following Brucella abortus and Brucella suis infection. Comparison of wild-type and deficient mice suggested that MZ macrophage population loss is dependent on interferon gamma (IFN-γ) receptor but independent of T cells or tumor necrosis factor alpha receptor 1 (TNF-αR1) signaling pathways and is not correlated to an alteration of CCL19, CCL21, and CXCL13 chemokine mRNA expression. Our results suggest that MZ macrophage populations are particularly sensitive to persistent low-level IFN-γ-mediated inflammation and that Brucella infection could reduce the ability of the spleen to perform certain MZM- and MMM-dependent tasks, such as antigen delivery to lymphocytes and control of systemic infection.

The increased ratio of CD4+/CD8+ was positively correlated with inflammation in hepatitis C patients with metabolic syndrome

BACKGROUND/AIMS

The incidence of metabolic syndrome (MS) in hepatitis C patients in Taiwan is not well known. Although the ratio of CD4(+)/CD8(+) T lymphocytes is considered to possibly affect the pathogenesis of hepatitis C, the effects of MS on CD4(+)/CD8(+) T lymphocytes remain unknown. The aims of this study to assess (1) the incidence of MS, (2) the inflammation status and fatty changes of liver, and (3) changes in their CD4(+)/CD8(+) T-lymphocyte ratio in patients with hepatitis C.

METHODS

60 hepatitis C patients were classified into MS or non-MS group. The terms of anthropometric data, MS components, and T-lymphocytes were assessed.

RESULTS

The proportion of hepatitis C patients suffering from MS was 26.7% in this study. The CD4(+)/CD8(+) T-lymphocyte ratios were higher in patients with MS than non-MS group. Hepatitis C patients with MS also had higher levels of ferritin than non-MS. Moreover, the level of ferritin positively correlated with the severity of fatty liver. The CD4(+)/CD8(+) T-lymphocyte ratio is also positively correlated with ferritin level and the severity of fatty liver.

CONCLUSIONS

Hepatitis C patients with MS had higher ratio of CD4(+)/CD8(+) T lymphocyte, which is associated with a high inflammatory response and a fatty change of liver.

High efficiency of antiviral CD4(+) killer T cells

The destruction of infected cells by cytotxic T lymphocytes (CTL) is integral to the effective control of viral and bacterial diseases, and CTL function at large has long been regarded as a distinctive property of the CD8(+)T cell subset. In contrast, and despite their first description more than three decades ago, the precise contribution of cytotoxic CD4(+)T cells to the resolution of infectious diseases has remained a matter of debate. In particular, the CTL activity of pathogen-specific CD4(+) "helper" T cells constitutes a single trait among a diverse array of other T cell functionalities, and overall appears considerably weaker than the cytolytic capacity of CD8(+) effector T cells. Here, using an in vivo CTL assay, we report that cytotoxic CD4(+)T cells are readily generated against both viral and bacterial pathogens, and that the efficiency of MHC-II-restricted CD4(+)T cell killing adjusted for effector:target cell ratios, precise specificities and functional avidities is comparable in magnitude to that of CD8(+)T cells. In fact, the only difference between specific CD4(+) and CD8(+)T cells pertains to the slightly delayed killing kinetics of the former demonstrating that potent CTL function is a cardinal property of both antiviral CD8(+) and CD4(+)T cells.

Regulatory T cells and Th17 cells in viral infections: implications for multiple sclerosis and myocarditis

In immune-mediated diseases, Treg and proinflammatory Th17 cells have been suggested to play either suppressor (beneficial) or effector (detrimental) roles, respectively. Tissue damage in viral infections can be caused by direct viral replication or immunopathology. Viral replication can be enhanced by anti-inflammatory responses and suppressed by proinflammatory responses. However, Tregs could suppress proinflammatory responses, reducing immunopathology, while Th17 cell-induced inflammation may enhance immunopathology. Here, the roles of Treg and Th17 cells depend on whether tissue damage is caused by direct virus replication or immunopathology, which differ depending on the virus, disease stage and host immune background. Although the precise mechanisms of tissue damage in multiple sclerosis and myocarditis are unclear, both viral replication and immune effector cells have been proposed to cause pathogenesis. Personalized medicine that alters the balance between Treg and Th17 cells may ameliorate viral pathology during infections.