Respiratory syncytial virus infection of airway epithelial cells, in vivo and in vitro, supports pulmonary antibody responses by inducing expression of the B cell differentiation factor BAFF.

BACKGROUND: The mechanisms regulating antibody expression within the human lung during airway infection are largely unknown. In this study, our objectives were to determine if infection with respiratory syncytial virus (RSV) upregulates expression of the B cell differentiation factors A proliferation inducing ligand (APRIL) and B cell activating factor of the TNF family (BAFF), if this is a common feature of viral airway infection, and how this is regulated in human airway epithelial cells. METHODS: We measured BAFF and APRIL protein expression in bronchoalveolar lavage (BAL) fluid from infants with severe RSV disease, and healthy control children, and in nasopharyngeal aspirates from preschool children with other single respiratory viral infections. We also measured mRNA expression in bronchial brushings from RSV-infected infants, and in RSV-infected paediatric primary airway epithelial cell cultures (pAEC). Beas-2B cell cultures were used to examine mechanisms regulating BAFF expression. RESULTS: BAFF protein and mRNA were elevated (in marked contrast with APRIL) in BAL and bronchial brushings, respectively, from RSV-infected infants. BAFF protein was also found in upper airway secretions from children with human metapneumovirus, H1N1, bocavirus, rhinovirus, RSV and Mycoplasma pneumoniae infection. BAFF mRNA and protein were expressed following in vitro RSV infection of both pAEC and Beas-2B cultures, with mRNA expression peaking 12-h postinfection. BAFF induction was blocked by addition of a neutralising anti-interferon-ß antibody or palivizumab. CONCLUSIONS: BAFF, produced through an interferon-ß-dependent process, is a consistent feature of airway infection, and suggests a role for the airway epithelia in supporting protective antibody and B cell responses in the lung.

Primary airway epithelial cultures from children are highly permissive to respiratory syncytial virus infection.

BACKGROUND: Respiratory syncytial virus (RSV) infection of airway epithelial cells (AECs) is an important initial event in RSV bronchiolitis. AEC immunological responses are thought to be critical in driving the subsequent inflammation in the airway. This study examined viral replication, cytotoxicity and cytokine production in cultures of primary AECs from children compared with responses to RSV infection in an immortalised epithelial cell line and to those from infants with RSV bronchiolitis. METHODS: RSV replication, proinflammatory cytokine responses and cytotoxicity in RSV-infected primary AEC cultures derived from bronchial brushings from the lungs of children were compared with those seen in BEAS-2B cultures, as well as AECs and bronchoalveolar lavage fluid collected from children with and without RSV bronchiolitis. RESULTS: Viral replication, cytotoxicity and inflammatory cytokine production were greater in primary AEC cultures than in BEAS-2B cells. Different response patterns were observed, with RSV infection of primary AEC cultures causing distinct peaks of viral replication and matched cytotoxic responses. Some primary AEC culture immunological responses, such as interleukin 8, were similar in magnitude to those seen in clinical samples from the lungs of children with RSV bronchiolitis. Although variable amounts of RSV were detected by PCR in freshly isolated primary AECs, RSV was not detected by immunocytochemistry. CONCLUSION: This is one of the first studies to examine comprehensively the responses to RSV infection in primary AEC cultures from children and shows marked differences from those of a commercially available immortalised human cell line but reassuring similarities to results found in vivo. This suggests that future work investigating responses of AECs to RSV infection should use primary AEC cultures.