MECHANISMS OF DISEASE Immunodeficiency and Genetic Defects of Pattern-Recognition Receptors

The susceptibility of adopted children to infection correlates more with the susceptibility of their biologic parents than with that of their adoptive parents.(1) This suggests that genetic factors can increase the risk of infection. These factors are often genetic polymorphisms, but in a few cases monogenic defects underlie vulnerability to repeated infections. Genetic studies of susceptibility to infection have typically focused on defects of antibody production, or a lack of T cells, phagocytes, natural killer cells, or complement, each of which can cause a classic immunodeficiency syndrome. Recently, genetic defects have been identified that impair recognition of pathogens by the innate immune system, increasing susceptibility to specific classes of microorganisms. For example, defects in the interferon-gamma pathway have been implicated in recalcitrant infections by intracellular pathogens such as mycobacteria and salmonella.(2,3) In this review, we focus on types of immunodeficiencies in which defects in pattern-recognition receptors and their downstream intracellular pathways predominate.