Modulation Of Paired Immunoglobulin-Like Type 2 Receptor Signaling Alters The Host Response To Staphylococcus Aureus-Induced Pneumonia

Paired immunoglobulin-like type 2 receptors (PILRs) inhibitory PILR alpha and activating PILR beta are predominantly expressed on myeloid cells. Their functions in host defense and inflammation are largely unknown, and in this study, we evaluated their roles in an acute Staphylococcus aureus pneumonia model. Compared to their respective controls, Pilrb(-/-) mice or mice in which PILR alpha was activated with an agonistic antibody showed improved clearance of pulmonary staphylococci and improved survival. These mice had reduced serum or bronchoalveolar lavage fluid levels of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha (TNF-alpha), and IL-6 and elevated levels of gamma interferon (IFN-gamma), IL-12, and IL-10. In contrast, mice in which PILR beta was activated had increased lung bacterial burdens and higher mortality coupled with an intense proinflammatory response with highly elevated levels of IL-1 beta, TNF-alpha, and IL-6. Treatment groups with reduced bacterial burdens had higher levels of Keratinocyte-derived chemokine (KC), macrophage inflammatory protein 2 (MIP-2), and MIP-1 alpha in bronchoalveolar lavage fluid and an increased influx of neutrophils and macrophages to the lungs. Consistent with our in vivo findings, bone marrow-derived macrophages from Pilrb(-/-) mice released significantly less IL-1 beta and TNF-alpha and more IFN-gamma and IL-12 than did the wild-type macrophages when directly stimulated with heat-killed S. aureus. To our knowledge, this is the first evidence that S. aureus directly interacts with PILR beta. It provides a mechanism by which manipulating the balance in favor of an inhibitory PILR signal, by activation of PILR alpha or deletion of PILR beta, helps to control acute S. aureus-mediated pneumonia and attenuate the inflammatory response. These results highlight the importance of PILRs in innate immunity and the control of inflammation.