Immune deficiency
In medicine, immune deficiency (or immunodeficiency) is a state where the immune system is incapable of defending the organism from infectious disease. There are roughly two types: congenital and acquired immune deficiency.
Congenital immune deficiency
A large number of rare diseases has been described that feature a heightened susceptibility to infections from childhood onward. Most of these disorders are hereditary and autosomal recessive. Defects are either of the humoral immunity, cell-mediated immunity or combined (such as in Severe Combined Immunodeficiency—SCID).
Acquired immune deficiency
Although elderly people are generally more susceptible to infections, this can be increased in the presence of a number of blood disorders (see hematology); important examples are multiple myeloma and chronic lymphatic leukemia (CLL).
Immune suppression is a common side-effect of many drugs, most importantly chemotherapy. This feature is used to suppress immune activity in autoimmune disorders with DMARDs. Any drug that causes neutropenia and/or agranulocytosis can cause immune suppression and sepsis.
Immune deficiency is also the hallmark of Acquired Immunodeficiency Syndrome (AIDS). AIDS invades CD4+-T-lymphocytes (Helper T cells), leading to opportunistic infections.