The International Union of Immunological Societies recognizes nine classes of primary immunodeficiencies, totaling approximately 430 conditions.[1][2] A 2014 update of the classification guide added a 9th category and added 30 new gene defects from the prior 2009 version.[3][4] The most recent classification was released in 2019.[5] The number of identified conditions continues to grow over time as more research is done.
The impact of primary immunodeficiencies ranges from mild to severe based on the condition.[6]
In primary antibody deficiencies, one or more isotypes of immunoglobulin are decreased or don't function properly. These proteins, generated by plasma cells, normally bind to pathogens, targeting them for destruction.[7]
B cells low but present or normal, but with reduction in 2 or more isotypes (usually IgG & IgA, sometimes IgM): common variable immunodeficiency (CVID), CD19 deficiency, TACI (TNFRSF13B) deficiency, BAFF receptor deficiency.
Phagocytes are the cells that engulf and ingest pathogens (phagocytosis), and destroy them with chemicals. Monocytes/macrophages as well as granulocytes are capable of this process. In certain conditions, either the number of phagocytes is reduced or their functional capacity is impaired.[7]
Several rare conditions are due to defects in the innate immune system, which is a basic line of defense that is independent of the more advanced lymphocyte-related systems. Many of these conditions are associated with skin problems.[7]
Rather than predisposing for infections, most of the autoinflammatory disorders lead to excessive inflammation. Many manifest themselves as periodic fever syndromes. They may involve various organs directly, as well as predisposing for long-term damage (e.g. by leading to amyloid deposition).[7]
The complement system is part of the innate as well as the adaptive immune system; it is a group of circulating proteins that can bind pathogens and form a membrane attack complex. Complement deficiencies are the result of a lack of any of these proteins. They may predispose to infections but also to autoimmune conditions.[7]