Early RSV infection aggravates asthma-related Th2 responses by increasing the number of CD4+ TRM cells through upregulation of PLZF

Abstract

Respiratory syncytial virus (RSV) infection is correlated with the chronic pathogenesis and exacerbation of asthma. However, the mechanism remains unclear. In this study, acute and memory (Mem) asthma models with early RSV infection are established to explore the persistence of the effects of RSV infection on asthma. Intravascular injection of an anti-CD45 antibody is performed to define CD4+ TRM cells accurately. RSV infection has a sustained impact on asthma exacerbation for at least six weeks, with high Th2 cytokine secretion in lung tissue instead of IgE response-related B cells. CD45–CD4+ TRM cells are positively correlated with RSV-related asthma exacerbation and severe airway inflammation. Mechanistically, overexpression of the transcription factor PLZF in vitro increases the number of CD4+ TRM cells, and conditional knockout of Zbtb16 (encoding PLZF) can decrease the number of CD4+ TRM cells to aggravate allergic inflammation and reduce Th2 responses. This study provides evidence for potential combined strategies that might benefit asthma patients.

1. Introduction

Respiratory syncytial virus (RSV) infection usually causes self-limited infections of the lung and respiratory tract. However, many studies have shown that children suffering from severe early RSV infections may have a higher incidence of recurrent wheezing and asthma in later childhood [1]. Children under 2 years of age with lower respiratory tract infections caused by RSV [2] are more susceptible to asthma [3,4]. The mechanism is not entirely clear. RSV-induced bronchiolitis can damage airways, promote airway obstruction and recurrent wheezing, and increase the risk for subsequent asthma [5]. Th2-related inflammation is one of the key pathogenic factors of allergic asthma [6]. RSV infection in early infancy was also found to preferentially promote Th2-like responses in the nose, with local production of IL-4 and IL-5 [7]. Many experiments have indicated that RSV infection can exacerbate asthma through the Th2 immune response, but the duration of its effects and the underlying molecular mechanism have not been elucidated [8,9].

Several reports have suggested that CD4+CD44+ memory T cells are involved in RSV infection and asthma [10–12]. There are several subtypes of memory T cells, including circulating memory T cells [i.e., effector memory T cells (TEMs) and central memory T cells (TCMs)] and tissue-resident memory T cells (TRMs) [13,14]. TRMs reside permanently in peripheral tissues, such as the skin, lung, and gut mucosa, where they provide localized immune protection without circulation through the blood or lymphatic system [15]. TRMs are generated in situ and provide rapid and persistent protection by proliferating and producing effector molecules such as cytokines (e.g., IFN-γ) and chemokines [16]. Conversely, TRMs have been shown to be key pathogenic factors in recurrent asthma in both BALB/c and C57 mice [16–18].

PLZF is a sequence-specific DNA-binding protein containing an N-terminal BTB/POZ domain and a C-terminal cluster of Krüppel-like C2H2 zinc fingers [19]. Interestingly, the functional state of PLZF can be altered in different cells and at different phases. PLZF expression at the innate lymphoid cell precursor stage promotes the functional properties of mature ILC2 proliferation for the innate allergic response [20]. Our previous study revealed that PLZF facilitates iNKT cell recruitment to the lung to promote immune tolerance to prevent asthma [21]. On the other hand, PLZF is essential for CD4+ T-cell development and can regulate the memory phenotype of CD44+ CD4+ T cells to promote the development of asthma tolerance [22]. These observations suggest that PLZF in CD4+ T cells influence the development of memory T cells and their expression, consequently affecting immune tolerance.