Encyclopedia of Health and Medicine

complement cascade 255
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 IMMUNOGLOBULIN G (IgG), a protein essential
for ANTIGEN recognition and antibody production.
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 infections.
Infections are most commonly upper respiratory,
SINUSES, THROAT, and middle EAR—typically
BRONCHITIS, PNEUMONIA, PHARYNGITIS, SINUSITIS, and
OTITIS media. Infections may be viral, bacterial, fungal,
or parasitic. Some people also have gastrointestinal
infections. The severity of infection varies
among people who have CVID as well as within an
individual from infection to infection. The diagnostic
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 infections)
and treatment with ANTIBIOTIC MEDICATIONS at
the first sign of infection. GAMMAGLOBULIN injections
can bolster the immune system, though the
gammaglobulin (which comes from blood or
PLASMA donors) may not contain the specific antibodies
the person needs. With effective medical
management and diligent prevention efforts, most
people who have CVID can enjoy relatively normal
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-
DERS such as RHEUMATOID ARTHRITIS or SYSTEMIC LUPUS
ERYTHEMATOSUS (SLE). Prompt diagnosis and appropriate
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 ANTIBODY binds 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 interactions
that take place with their activation ultimately
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 antibody-marked
cell. This penetration kills the cell
and coats it in proteins that mark it for PHAGOCYTO-
SIS, the process through which LEUKOCYTE (white
BLOOD cell) scavenger cells, called phagocytes, consume
the debris that remains after the attacked
cell dies.
There are about 30 complement proteins, also
called complement factors, in the blood circulation.
They remain inactive until antibody–antigen
bindings or certain other immune responses activate
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. Disintegration
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 certain
AUTOIMMUNE DISORDERS such as SYSTEMIC LUPUS
ERYTHEMATOSUS (SLE). Complement activity also
diminishes in GRAFT VS. HOST DISEASE.