Streptococcal
pneumonia is a worldwide health problem that kills ∼2 million people each year, particularly young children, the elderly, and immunosuppressed individuals. Alveolar macrophages and neutrophils provide the early innate immune response to clear pneumococcus from infected lungs. However, the level of neutrophil involvement is context dependent, both in humans and in mouse models of the disease, influenced by factors such as bacterial load, age, and
coinfections. Here, we show that the
G protein-coupled receptor (GPCR) adaptor
protein norbin (
neurochondrin, NCDN), which was hitherto known as a regulator of neuronal function, is a suppressor of neutrophil-mediated innate immunity. Myeloid
norbin deficiency improved the immunity of mice to
pneumococcal infection by increasing the involvement of neutrophils in clearing the bacteria, without affecting neutrophil recruitment or causing autoinflammation. It also improved immunity during Escherichia coli-induced septic
peritonitis. It increased the responsiveness of neutrophils to a range of stimuli, promoting their ability to kill bacteria in a
reactive oxygen species-dependent manner, enhancing degranulation, phagocytosis, and the production of
reactive oxygen species and neutrophil extracellular traps, raising the cell surface levels of selected GPCRs, and increasing GPCR-dependent Rac and Erk signaling. The Rac
guanine-nucleotide exchange factor Prex1, a known effector of
norbin, was dispensable for most of these effects, which suggested that
norbin controls additional downstream targets. We identified the Rac
guanine-nucleotide exchange factor Vav as one of these effectors. In summary, our study presents the GPCR adaptor
protein norbin as an immune suppressor that limits the ability of neutrophils to clear
bacterial infections.