Facts on File Encyclopedia of Health and Medicine

common variable immunodeficiency (CVID)
An immune disorder in which the IMMUNE SYSTEM
lacks the ability to produce adequate antibodies to
protect the body from INFECTION. Though there are
normal numbers of B-lymphocytes in the BLOOD
circulation, these ANTIBODY-producing cells are
lacking IMMUNOGLOBULING (IgG), a protein essen-
tial for ANTIGENrecognition and antibody produc-
tion. IgG is the foundation for most antibodies
that the immune system produces.

Symptoms and Diagnostic Path

Symptoms of CVID can show up any time after
about age 10 though most commonly appear in the
late 20s and early 30s. Generally the person has the
same type of infection repeatedly, as the immune
system is not producing antibodies to protect
against the infectious agent. The key symptom is a
progressive pattern of recurrent or chronic infec-
tions. Infections are most commonly upper respira-
tory, SINUSES, THROAT, and middle EAR—typically
BRONCHITIS, PNEUMONIA, PHARYNGITIS, SINUSITIS, and
OTITISmedia. Infections may be viral, bacterial, fun-
gal, or parasitic. Some people also have gastroin-
testinal infections. The severity of infection varies
among people who have CVID as well as within an
individual from infection to infection. The diagnos-
tic path includes blood tests to measure IgG and
antibody levels. Immunoglobulin A (IgA) and
immunoglobulin M (IgM) levels may also be low.

Treatment Options and Outlook

The main therapeutic course is reducing exposure
to known infection (such as common viral infec-
tions) and treatment with ANTIBIOTIC MEDICATIONSat
the first sign of infection. GAMMAGLOBULINinjec-
tions can bolster the immune system, though the
gammaglobulin (which comes from blood or
PLASMAdonors) may not contain the specific anti-
bodies the person needs. With effective medical
management and diligent prevention efforts, most
people who have CVID can enjoy relatively nor-
mal lifestyles and life expectancy.

Risk Factors and Preventive Measures
Most CVID is acquired, though researchers do not
know what causes it to occur. There are no known
measures for preventing CVID. CVID occurs more

frequently in people who have AUTOIMMUNE DISOR-

DERSsuch as RHEUMATOID ARTHRITISor SYSTEMIC LUPUS

ERYTHEMATOSUS(SLE). Prompt diagnosis and appro-

priate treatment are essential for preventing

substantial lung damage that can occur from

recurrent infections.

See also BACTERIA; FUNGUS; HAND WASHING; LUNGS;

PARTIAL COMBINED IMMUNODEFICIENCY(PCID); PARASITE;

PERSONAL HYGIENE; SEVERE COMBINED IMMUNODEFI-

CIENCY(SCID); LIVING WITH IMMUNE DISORDERS; VIRUS.

complement cascade The series of events that

take place when an ANTIBODYbinds with an ANTI-

GEN, activating the complements. Complements

are proteins that participate in immune and

inflammatory processes, acting primarily to kill

antibody-marked cells. The biochemical interac-

tions that take place with their activation ulti-

mately lead to the formation of a protein structure

called the terminal complement component or the

membrane attack complex. The membrane attack

complex penetrates the cell membrane of the anti-

body-marked cell. This penetration kills the cell

and coats it in proteins that mark it for PHAGOCYTO-

SIS, the process through which LEUKOCYTE(white

BLOODcell) scavenger cells, called phagocytes, con-

sume the debris that remains after the attacked

cell dies.

There are about 30 complement proteins, also

called complement factors, in the blood circula-

tion. They remain inactive until antibody–antigen

bindings or certain other immune responses acti-

vate them. Doctors classify activated complements

into nine major molecular complexes identified as

C1–C9. C1–C4 form the preliminary pathways

leading to the formation of the membrane attack

complex. C5–C9 collectively form the membrane

attack complex. Other proteins interact with the

complements to keep their actions in check. Disin-

tegration of the complement complexes begins

immediately after their activation to prevent them

from damaging other cells.

Blood tests can measure complement activity in

the body. Complement activity is often increased

in the presence of cancer and decreased with cer-

tain AUTOIMMUNE DISORDERSsuch as SYSTEMIC LUPUS

ERYTHEMATOSUS (SLE). Complement activity also

diminishes in GRAFT VS. HOST DISEASE.

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