Differential impact of ageing on cellular and humoral immunity to a persistent murine gamma-herpesvirus

T-Cell Immunity to Influenza in Older Adults: A Pathophysiological Framework for Development of More Effective Vaccines

One of the most profound public health consequences of immune senescence is reflected in an increased susceptibility to influenza and other acute respiratory illnesses, as well as a loss of influenza vaccine effectiveness in older people. Common medical conditions and mental and psychosocial health issues as well as degree of frailty and functional dependence accelerate changes associated with immune senescence. All contribute to the increased risk for complications of influenza infection, including pneumonias, heart diseases, and strokes that lead to hospitalization, disability, and death in the over 65 population. Changes in mucosal barrier mechanisms and both innate and adaptive immune functions converge in the reduced response to influenza infection, and lead to a loss of antibody-mediated protection against influenza with age. The interactions of immune senescence and reduced adaptive immune responses, persistent cytomegalovirus infection, inflammaging (chronic elevation of inflammatory cytokines), and dysregulated cytokine production, pose major challenges to the development of vaccines designed to improve T-cell-mediated immunity. In older adults, the goal of vaccination is more realistically targeted to providing clinical protection against disease rather than to inducing sterilizing immunity to infection. Standard assays of antibody titers correlate with protection against influenza illness but do not detect important changes in cellular immune mechanisms that correlate with vaccine-mediated protection against influenza in older people. This article will discuss: (i) the burden of influenza in older adults and how this relates to changes in T-cell function, (ii) age-related changes in different T-cell subsets and immunologic targets for improved influenza vaccine efficacy in older, and (iii) the development of correlates of clinical protection against influenza disease to expedite the process of new vaccine development for the 65 and older population. Ultimately, these efforts will address the public health need for improved protection against influenza in older adults and “vaccine preventable disability.”

Mechanisms of immunosenescence: lessons from models of accelerated immune aging

With increasing age, the ability of the adaptive immune system to respond to vaccines and to protect from infection declines. In parallel, the production of inflammatory mediators increases. While cross-sectional studies have been successful in defining age-dependent immunological phenotypes, studies of accelerated immune aging in human subpopulations have been instrumental in obtaining mechanistic insights. The immune system depends on its regenerative capacity; however, the T cell repertoire, once established, is relatively robust to aging and only decompensates when additionally stressed. Such stressors include chronic infections such as CMV and HIV, even when viral replication is controlled, and autoimmune diseases. Reduced regenerative capacity, chronic immune activation in the absence of cell exhaustion, T cell memory inflation, and accumulation of highly potent effector T cells in these patients synergize to develop an immune phenotype that is characteristic of the elderly. Studies of accelerated immune aging in autoimmune diseases have identified an unexpected link to chronic DNA damage responses that are known to be important in aging, but so far had not been implicated in immune aging.

Importance of antibody in virus infection and vaccine-mediated protection by a latency-deficient recombinant murine γ-herpesvirus-68

The human γ-herpesviruses EBV and Kaposi's sarcoma-associated herpesvirus establish lifelong latent infections, can reactivate in immunocompromised individuals, and are associated with the development of malignancies. Murine γ-herpesvirus-68 (γHV68), a rodent pathogen related to EBV and Kaposi's sarcoma-associated herpesvirus, provides an important model to dissect mechanisms of immune control and investigate vaccine strategies. Infection of mice with γHV68 elicits robust antiviral immunity, and long-term protection from γHV68 reactivation requires both cellular and humoral immune responses. Vaccination of mice with AC-replication and transcription activator (RTA), a highly lytic latency-null recombinant γHV68, results in complete protection from wild-type γHV68 infection that lasts for at least 10 mo. In this report, we examine the immune correlates of AC-RTA-mediated protection and show that sterilizing immunity requires both T cells and Ab. Importantly, Ab was also critical for mitigating viral infection in the brain, and in the absence of Ab-mediated control, amplification of the AC-RTA virus in the brain resulted in fatality. Our results highlight important considerations in the development of vaccination strategies based on live-attenuated viruses.

Pulmonary fibrosis induced by γ-herpesvirus in aged mice is associated with increased fibroblast responsiveness to transforming growth factor-β

Young (4 month) and aged (15-18 months) mice were given intranasal saline or γ--herpesvirus-68 infection. After 21 days, aged, but not young mice, showed significant increases in collagen content and fibrosis. There were no differences in viral clearance or inflammatory cells (including fibrocytes) between infected aged and young mice. Enzyme-linked immunosorbent assays showed increased transforming growth factor-β in whole lung homogenates of infected aged mice compared with young mice. When fibroblasts from aged and young mice were infected in vitro, aged, but not young, fibroblasts upregulate alpha-smooth muscle actin and collagen I protein. Infection with virus in vivo also demonstrates increased alpha-smooth muscle actin and collagen I protein and collagen I, collagen III, and fibronectin messenger RNA in aged fibroblasts. Furthermore, evaluation revealed that aged fibroblasts at baseline have increased transforming growth factor-β receptor 1 and 2 levels compared with young fibroblasts and are resistant to apoptosis. Increased responsiveness to transforming growth factor-β was verified by increased collagen III and fibronectin messenger RNA after treatment in vitro with transforming growth factor-β.

Viral infection and aging as cofactors for the development of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a disease of unknown origin and progression that primarily affects older adults. Accumulating clinical and experimental evidence suggests that viral infections may play a role, either as agents that predispose the lung to fibrosis or exacerbate existing fibrosis. In particular, herpesviruses have been linked with IPF. This article summarizes the evidence for and against viral cofactors in IPF pathogenesis. In addition, we review mechanistic studies in animal models that highlight the fibrotic potential of viral infection, and explore the different mechanisms that might be responsible. We also review early evidence to suggest that the aged lung may be particularly susceptible to viral-induced fibrosis and make recommendations for future research directions.