An immunodeficiency can cause frequent and recurrent infections of varying severity. The disorder may be due to underlying medical conditions or treatments for these conditions.
This is termed secondary (acquired) immunodeficiency and is a much more common reason for recurrent infections in adults. A less common cause is primary (congenital) immunodeficiency, which typically presents in infancy or early childhood.
Primary immunodeficiency typically denotes inherited abnormalities of the immune system. Primary immunodeficiency can affect T-cells, B-cells, phagocytic cells or the complement system.
Most primary immune deficiencies are inherited diseases that appear to run in families; examples include X-linked agammaglobulinemia (XLA) and severe combined immunodeficiency (SCID). Other primary immune deficiencies, such as common variable immunodeficiency (CVID), are not as obvious as to whether they are inherited. The causes of the defects are unknown and genetic factors cannot be ruled out.
Secondary immunodeficiency occurs when the function of the immune system is disrupted secondary to an underlying disease state, medications, surgery or other medical procedure. Radiation, chemotherapy, burns, chronic illness and malignancies can cause secondary immunodeficiency. Infections with the Human Immunodeficiency Virus (HIV) can cause a secondary immunodeficiency known as Acquired Immune Deficiency Syndrome (AIDS). Chemotherapy treatments can cause a secondary immunodeficiency called neutropenia. In leukemia and multiple myeloma, cancerous immune cells crowd out the normal stem cells of the bone marrow. These abnormal cells reduce the number of B-cells and lead to hypogammaglobinemia, another type of secondary immunodeficiency.
There are over 400 known primary immunodeficiencies and the number of secondary immunodeficiencies is also large.