Abstract
Innate immunity is the host's first line of defence against infection. In this review, we present the innate immune response implicated in three examples of pulmonary infection of viral, fungal and bacterial origin. We show that this defence against infection can be a double-edged sword. Thus, the same cells, molecules and mechanisms involved in this protective process can also be involved in deleterious inflammation. A delicate balance between immunity and inflammation is therefore required, making it possible to fight pathogens effectively while limiting inflammation that might be damaging to the host.