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Human primary immunodeficiencies PIDs comprise a broad group of inherited disorders characterised by developmental or functional defects of myeloid or lymphoid haemapoietic-derived cells, as well as non-haemapoietic cells involved in protective immunity. More than different forms of PIDs affecting distinct components of the innate and adaptive immune system, such as neutrophils, macrophages, dendritic cells, complement proteins, natural killer cells, and T and B lymphocytes have been described [ 1 ].
Clinically, PIDs can be associated with any combination of infectious disease, autoimmunity, auto-inflammatory, allergy and malignancy. The best known PIDs show Mendelian inheritance and first become symptomatic during childhood. Conventional PIDs are typically seen as rare monogenic conditions associated with detectable immunologic abnormalities, resulting in a broad susceptibility to multiple and recurrent infections caused by weakly pathogenic and more virulent microorganisms.
By opposition to these conventional PIDs, nonconventional primary immunodeficiencies as Mendelian conditions manifesting in otherwise healthy patients as a narrow susceptibility to infections, recurrent or otherwise, caused by weakly pathogenic or more virulent microbes are now reported [ 2 ]. By now, up to disease-causing genes have been identified. This molecular characterisation of PIDs has helped to increase our understanding of their physiopathology.
The study of these diseases has provided essential insights into the functioning of the immune system with the ultimate goal of facilitating diagnosis and treatment. Primary immunodeficiency diseases are a heterogeneous group of disorders, caused by inherited defects in the immune system, and characterised by wide spectrum of clinical manifestations, particularly an increased susceptibility to infections and a predisposition to autoimmune diseases and malignancies.
