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phytoimmunity 573 pituitary autoantibodies
acting as accessory cells; these cells do not respond to
PHA. PHA binds to glycoproteins on T cell surfaces.
phytoimmunity
Both active and passive immune-like phenomena in
plants. Plant substances active in phytoimmunity include
phytonicides and phytoalexins. Plant resistance to many
diseases is associated with the presence of antibiotic
substances in plant tissues. Antibiotic substances are
inherent in both susceptible and resistant varieties. They
may be constitutional inhibitors present in a plant before
contact with a parasite or induced antibiotic substances
that arise after contact with a parasite. Defense reactions
in plants that are associated with the formation and
conversion of antibiotic substances include reactions to
wounding and necrotic reactions. Plant resistance to a
specific disease is determined by the various antibiotic
substances they contain and the synergistic actions of
these agents with differing roles in phytoimmunity. Plant
varieties differ in the quantities of antibiotic substances
present in intact tissues and the intensity of their generation
in response to infection. They also differ in the
nature of subsequent conversions that may produce a
marked increase in antibiotic activity.
phytomitogens
Plant glycoproteins that activate lymphocytes through stimulation
of DNA synthesis and induction of blast transformation.
phytonicides
Substances produced in both traumatized and nontraumatized
plants that represent factors active in plant immunity.
Phytonicides have bactericidal, fungicidal, and protisticidal
properties.
PI
Abbreviation for primary immunodeficiency.
picornavirus
Small RNA virus with a naked capsid structure. More than
230 viruses categorized as enteroviruses, rhinoviruses,
cardioviruses, and aphthoviruses comprise this family.
picornavirus immunity
Neutralizing antibodies play an important role in protection
against picornaviruses as shown by the ability of passively
transferred antibodies to block virus replication and disease
progression. The early IgM response is less specific than
the subsequent IgG and IgA responses. Considerable cross
reactivity exists among the different serotypes. Virus neutralization
by antibody involves Fc receptor-mediated endocytosis
(opsonization) and interactions that prevent virus
penetration and uncoating or induce lethal RNA unpackaging.
CD4 + T cells have also been shown to be significant in
picornavirus infections that induce cell-mediated responses
with the production of cytokines. CD4 + and CD8 + T lymphocytes
recognize specific epitopes. Picornaviruses evade
the immune system through antigenic variation of neutralizing
antibody epitopes and may also involve variation at
T cell sites and MHC-binding structures that interfere with
help for humoral immune responses and cell-mediated
killing of infected cells. Vaccines against picornaviruses
depend on their ability to induce neutralizing antibodies in
the host following administration of a live attenuated virus
or a chemically inactivated intact virus.
picryl chloride (1-chloro-2,4,6-trinitrobenzene)
A substance used to add picryl groups to proteins. When
applied to the skin of an experimental animal such as a
guinea pig, a solution of picryl chloride may conjugate with
skin proteins, where it acts as a hapten and may induce
contact (type IV) hypersensitivity.
piecemeal necrosis
Deaths of individual liver cells that are encircled by lymphocytes
in chronic active hepatitis.
pigeon breeder’s lung
Hypersensitivity pneumonitis. Also called pigeon
fancier’s lung.
pili
Structures that facilitate adhesion of bacteria to host cells
and are therefore direct determinants of virulence.
Louis Pillemer.
Pillemer, Louis (1908–1957)
Professor at Western Reserve University (now Case Western
Reserve) who described properdin and the alternative pathway
of complement activation.
pinocytosis
The uptake by a cell of small liquid droplets, minute particles,
and solutes.
Pirquet von Cesenotics, Clemens Peter Freiherr von
(1874–1929)
Viennese physician who coined the term allergy and
described serum sickness and its pathogenesis. He also
developed a skin test for tuberculosis. He held academic
appointments at Vienna, Johns Hopkins, and Breslau and
returned to Vienna in 1911 as director of the University
Children’s Clinic. (Refer to Die Serumkrenkheit [with
Schick], 1905; Klinische Studien über Vakzination und
Vakzinale Allergie, 1907; Allergy, 1911.)
pituitary autoantibodies
Autoantibodies most often found in the empty sella syndrome.
They are less often found in the sera of patients with
pituitary adenomas, prolactinomas, acromegaly, idiopathic
diabetes insipidus, Hashimoto’s thyroiditis, Graves’ disease,
and POEMS (polyneuropathy, organomegaly, endocrinopathy,
M protein, and skin changes) syndrome. They are also associated
with insulin-dependent diabetes mellitus (IDDM)
P