Immunodeficiency, Primary: Affecting the Adaptive Immune System

Adaptive immune mechanisms recognize and neutralize foreign molecules or microorganisms in a specific manner. Lymphocytes, B and T cells, can respond specifically to thousands of nonself materials. Adaptation is further acquired with memory of previous infections. Immunodeficiencies impair the functioning of the immune system. Deficiencies are highly variable with regard to symptoms, phenotype, genotype, severity, etc. because many cells and molecules are required for both natural and adaptive immunity. However, increased susceptibility to infection is common to all immunodeficiencies. See also: Cells of the immune system; Immunodeficiency; Immune system Close to 150 primary immune deficiencies (PIDs) are now known, and have been grouped according to the components of the immune system affected (International Union of Immunological Societies, 1999; Buckley, 2000; Bonilla and Geha, 2003; ImmunoDeficiency Resource). Most PIDs are relatively rare disorders. Antibody deficiency disorders are defects in immunoglobulin-producing B cells (Table 1). T cells, which are responsible for killing infected cells or helping other immune cells, can also be targets for immunodeficiency disorders. These disorders usually result in combined immune deficiencies (CIDs), where both T cells and antibody production are defective. Other immunodeficiencies affect the complement system or phagocytic cells, impairing antimicrobial immunity. Secondary immunodeficiencies may allow similar infections to PIDs, but are associated with some other factors such as malnutrition, age, drugs, tumours or infections, including human immunodeficiency virus (HIV). See also: B lymphocytes; Immunodeficiency disorders due to antibody deficiency (B lymphocyte disorders); Immunodeficiency: secondary; T lymphocytes: helpers The incidence of PIDs varies greatly from about 1:500 births with selective IgA deficiency to only a few known cases of the rarest disorders. Patients with antibody deficiencies are particularly susceptible to encapsulated bacteria, such asHaemophilus influenzae, Staphylococcus aureus and Streptococcus pneumoniae, which cause pyogenic infections. T-cell immunodeficiencies and severe CIDs (SCIDs) are marked by opportunistic infections caused by common environmental microorganisms. Patients with PIDs have recurrent serious infections starting soon after birth. Life-threatening symptoms can arise within the first few days of life in SCID. However, in immunoglobulin (Ig) deficiencies, children are protected for 6–12 months by the maternal IgG. See also: Immunodeficiency: severe combined immunodeficiency; Infections in the immunocompromised host The infections in PID patients require prolonged treatment with antibiotics at high doses. Antibody deficiencies are treated with intravenous immunoglobulin substitution therapy. Gammaglobulins are extracted from human blood from donor pools. Leucocytes (B and T cells) are produced from stem cells in bone marrow. In SCIDs bone Article