Human metapneumovirus infection activates the TSLP pathway that drives excessive pulmonary inflammation and viral replication in mice

Abstract

Human metapneumovirus (hMPV) is a leading cause of acute respiratory tract infections in children and the elderly. The mechanism by which this virus triggers an inflammatory response still remains unknown. Here, we evaluated whether the thymic stromal lymphopoietin (TSLP) pathway contributes to lung inflammation upon hMPV infection. We found that hMPV infection promotes TSLP expression both in human airway epithelial cells and in the mouse lung. hMPV infection induced lung infiltration of OX40L + CD11b + DCs. Mice lacking the TSLP receptor deficient mice (tslpr −/− ) showed reduced lung inflammation and hMPV replication. These mice displayed a decreased number of neutrophils as well a reduction in levels of thymus and activation-regulated chemokine/CCL17, IL-5, IL-13, and TNF-α in the airways upon hMPV infection. Furthermore, a higher frequency of CD4 + and CD8 + T cells was found in tslpr −/− mice compared to WT mice, which could contribute to controlling viral spread. Depletion of neutrophils in WT and tslpr −/− mice decreased inflammation and hMPV replication. Remarkably, blockage of TSLP or OX40L with specific Abs reduced lung inflammation and viral replication following hMPV challenge in mice. Altogether, these results suggest that activation of the TSLP pathway is pivotal in the development of pulmonary pathology and pulmonary hMPV replication.Keywords: Dendritic cells r hMPV r Inflammation r Neutrophils r OX40L r TSLP r Viral replication Additional supporting information may be found in the online version of this article at the publisher's web-site Correspondence: Dr. Alexis M. Kalergis e-mail: akalergis@bio.puc.cl * These authors contributed equally to this work.C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2015. 45: 1680-1695 Immunity to infection 1681 IntroductionHuman metapneumovirus (hMPV) is an enveloped virus that belongs to the Paramyxoviridae family, Pneumovirinae subfamily, and the Metapneumovirus genus. The hMPV genome consists of a 13.3-kb single-stranded, negative-sense RNA encoding eight messenger RNAs, which are transcribed directly from the viral genome and translated into nine different polypeptides [1,2]. hMPV was described for the first time in 2001 as a pathogen responsible for acute respiratory tract infections in children [3]. Today, hMPV is considered the second most relevant etiological agent of acute upper and lower respiratory tract infections in children, the elderly, and immunocompromised adults [4]. Furthermore, in young children, hMPV is the second most reported cause of bronchiolitis and pneumonia after human respiratory syncytial virus (hRSV), accounting for ß10% of pediatric hospitalizations related to acute respiratory tract infection [5][6][7]. In addition, hMPV is the cause of outbreaks of acute respiratory tract infections with more than 10% mortality in elderly patients [8,9]. Currently, neither safe-effective vaccines nor specific antiviral therapies are available for hMPV, although promising candidate vaccines have recently be...

Aberrant T cell immunity triggered by human Respiratory Syncytial Virus and human Metapneumovirus infection

“…135,136 A recent in vivo study, though, showed mixed T H 1 and T H 2 responses during the first week of hMPV infection in BALB/c mice. 141 Consistent with the notion observed in the mouse model, in adults undergoing hMPV infection, it has been described that PBMCs from these patients presented cytolitic activity, as evaluated by a Chrome-release assay, which suggest a T H 1 response. 142 However, PBMCs, from healthy adults, stimulated with heat-inactivated hMPV promotes the induction of high levels IL-6 (a T H 2 polarizing cytokine that prevents T H 1 differentiation 143 ) and low levels of IFN-g and CCR5 (T H 1 cytokines) when compare with hRSV-stimulated PBMCs, thus suggesting a polarization toward a T H 2 response.…”

“…Related to this, hMPV infection has been proven: to promote TSLP expression in both human AECs and mouse lungs; to stimulate OX40LCCD11bCDCs lung infiltration; and to increase the levels of pro-inflammatory TH2 cytokines-producing T cells, including TARC, IL-5 and IL-13, but also TNF-a in BALB/c mice, 141 as previously reported for OX40L on TSLP-activated DCs. 86 Moreover, TSLPR¡/¡ mice showed decreased lung inflammation and hMPV replication, as well as a higher frequency of CD8…”

“…141 These findings highlight the possibility that a repertoire of virus-specific T H and CTLs may incompletely eliminate infected cells within the airways following primary infection, leading to an exacerbated inflammatory response, mainly mediated by the TSLP pathway, thus inducing an aberrant T cell response. 141 Moreover, hMPV-infected DCs, similarly to hRSVinfected DCs, also impair the activation of CD4 C T cells.…”

“…141 These findings highlight the possibility that a repertoire of virus-specific T H and CTLs may incompletely eliminate infected cells within the airways following primary infection, leading to an exacerbated inflammatory response, mainly mediated by the TSLP pathway, thus inducing an aberrant T cell response. 141 Moreover, hMPV-infected DCs, similarly to hRSVinfected DCs, also impair the activation of CD4 C T cells. Upon stimulation with hMPV-infected and antigen loaded DCs, na€ ıve antigen-specific CD4 C T cells displayed significantly reduced proliferation, expression of surface activation markers, such as CD25 (IL-2 receptor/ IL-2Ra), CD69 and CD71 (transferrin receptor) and IL-2 secretion, as compare with T cells stimulated with uninfected control DCs.…”

“…149 On the other hand, the depletion of CD8 C T cells in hMPV-infected BALB/c mice resulted in a lower lung pathological score, although to a lesser degree than depletion of only CD4 C T cells. 140 By other part, mice that was depleted of neutrophils showed a significant reduction of TNF-a and IL-13 secreted by CD8 C T cells suggesting that neutrophils modulate the production of these cytokines by CD8 C T cells, 141 In this manner, CD8 C T cells that infiltrate in the airways and secrete TNF-a and IL13 contribute to the lung pathology triggered by hMPV infection in mice. 140,141 Taken together, CD8 C T cells confer protection against hMPV infection through cytotoxic activities, but these cells may also contribute to lung pathology.…”