Inflammation triggered by influenza A virus (IAV) infection is important for viral clearance, induction of adaptive responses and return to lung homeostasis. However, an exaggerated immune response, characterized by the overproduction of chemokines, can lead to intense lung injury, contributing to mortality. Chemokine scavenger receptors, such as ACKR2, control the levels of CC-chemokines influencing the immune responses. Among the chemokine targets of ACKR2, CCL5 is important to recruit and activate lymphocytes.
We investigated the role of ACKR2 during IAV infection in mice.
Pulmonary ACKR2 expression was increased acutely after IAV infection preceding the virus-induced lung dysfunction. ACKR2-knockout (ACKR2) mice were protected from IAV presenting decreased viral burden and lung dysfunction. Mechanistically, the absence of ACKR2 resulted in augmented airway CCL5 levels, secreted by mononuclear and plasma cells in the lung parenchyma. The higher chemokine gradient led to an augmented recruitment of T and B-lymphocytes, formation of iBALT and production of IgA in the airways of ACKR2 mice post-IAV. CCL5 neutralization in ACKR2 mice prevented lymphocyte recruitment and increased BALF protein levels and pulmonary dysfunction. Finally, CCR5 mice presented increased disease severity during IAV infection, displaying increased neutrophils, pulmonary injury and dysfunction, and accentuated lethality.
Collectively, our data showed that ACKR2 dampens CCL5 levels and the consequent recruitment of CCR5 Th1, Treg and B-lymphocytes during IAV infection, decreasing pathogen control and promoting lung dysfunction in wild type mice. Therefore, ACKR2 is detrimental and CCR5 is protective during IAV infection coordinating innate and adaptive immune responses in mice.