[Primary and secondary immunodeficiencies]

Primary Immunodeficiencies (PID) are rare, genetically determined diseases that cause dysfunctional immunity, clinically presenting as susceptibility to infection but also as autoimmunity due to deficient immune tolerance. More than 180 PID have been described to date. To diagnose a PID, secondary causes of immunodeficiency have to be excluded which can be especially challenging in the adult population. PID associated with hypogammaglobulinemia are treated by immunoglobulin replacement therapy, while the correction of the underlying cellular immune defects is often not possible. This review focuses on PID and secondary causes of immunodeficiency that occur in the adult population and discusses patho-mechanisms of select immunodeficiencies and associated immune dysregulation.