P–R
partial combined immunodeficiency (PCID) An
immune disorder in which the IMMUNE SYSTEMis
missing key components. Most often people who
have PCID lack certain leukocytes (white BLOOD
cells), which impairs their ability to form antibod-
ies (develop IMMUNITY) and fight INFECTION. The
abnormality might be with cell differentiation,
maturity, or function. Sometimes PCID involves
deficits of complement factors, the specialized pro-
teins that activate ANTIBODY–ANTIGEN binding.
Symptoms of PCID vary somewhat, depending on
the immune deficit though generally include fre-
quent infections and autoimmune reactions. Com-
mon infections are PNEUMONIA and CANDIDIASIS
(thrush). OPPORTUNISTIC INFECTIONmay also occur.
Autoimmune reactions often involve the SKIN,
appearing as atopic DERMATITISand other rashes.
The diagnostic path typically includes blood
tests that measure the types and quantities of
white blood cells, IMMUNOGLOBULIN, and comple-
ment factors. GENETIC TESTING may identify the
presence of GENETIC DISORDERSthat have IMMUNODE-
FICIENCYcomponents. Treatment varies according
to the immunodeficiency and severity of symp-
toms, though usually includes ANTIBIOTIC MEDICA-
TIONS to control infections and GAMMAGLOBULIN
injections to bolster the IMMUNE RESPONSE.
See alsoANTIBODY-MEDIATED IMMUNITY; CELL-MEDI-
ATED IMMUNITY; COMMON VARIABLE IMMUNODEFICIENCY
(CVID); COMPLEMENT CASCADE; IMMUNE DISORDERS;
LEUKOCYTE; LIVING WITH IMMUNE DISORDERS; RASH;
SEVERE COMBINED IMMUNODEFICIENCY(SCID).
passive immunity IMMUNITY (protection from
INFECTION) that occurs without activation of the
IMMUNE RESPONSE. A newborn has passive immunity
from the antibodies in his or her mother’s BLOODat
the time of birth and continues to receive limited
ANTIBODYprotection for the duration of BREASTFEED-
ING. Passive immunity also occurs when a person
receives GAMMAGLOBULINthat contains antibodies
present in the blood (PLASMA) of the donors who are
the source for the gammaglobulin.
For further discussion of immunity within the
context of the structures and functions of the
immune system, please see the overview section
“The Immune System and Allergies.”
See also ACTIVE IMMUNITY; INNATE IMMUNITY.Peyer’s patches Small, nodular clusters of lym-
phoid tissue scattered throughout the mucous
membrane lining of the SMALL INTESTINE. Though
not encapsulated as are LYMPH NODES, Peyer’s
patches are more distinct and organized than
other MUCOSA-ASSOCIATED LYMPHOID TISSUE (MALT).
Peyer’s patches are elements of GUT-ASSOCIATED
LYMPHOID TISSUE(GALT), a subset of MALT. GALT lies
beneath the epithelial tissue (mucosal lining) of
the gastrointestinal tract. Peyer’s patches contain
concentrations of B-cell lymphocytes that actively
produce antibodies. They also contain some T-cell
lymphocytes and phagocytic cells to enhance the
IMMUNE RESPONSEin the small intestine.
For further discussion of Peyer’s patches within
the context of the structures and functions of the
immune system, please see the overview section
“The Immune System and Allergies.”
See also ANTIBODY; B-CELL LYMPHOCYTE; LYMPHO-
CYTE; PHAGOCYTE; T-CELL LYMPHOCYTE.prostaglandins A large family of fast-acting lipid
mediators primarily responsible for initiating
INFLAMMATION, FEVER, and PAINduring the IMMUNE
RESPONSE. Prostaglandins are also vital for numer-
ous functions throughout the body. Thromboxane,
one of the prostaglandins, facilitates PLATELET289