Primary immunodeficiencies in cytosolic pattern-recognition receptor pathways: Toward host-directed treatment strategies

In the last decade, the paradigm of primary immunodeficiencies (PIDs) as rare recessive familial diseases that lead to broad, severe, and early-onset immunological defects has shifted toward collectively more common, but sporadic autosomal dominantly inherited isolated defects in the immune response. Patients with PIDs constitute a formidable area of research to study the genetics and the molecular mechanisms of complex immunological pathways. A significant subset of PIDs affect the innate immune response, which is a crucial initial host defense mechanism equipped with pattern-recognition receptors. These receptors recognize pathogen- and damage-associated molecular patterns in both the extracellular and intracellular space. In this review, we will focus on primary immunodeficiencies caused by genetic defects in cytosolic pattern-recognition receptor pathways. We discuss these PIDs organized according to their mutational mechanisms and consequences for the innate host response. The advanced understanding of these pathways obtained by the study of PIDs creates the opportunity for the development of new host-directed treatment strategies.