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adiation bone marrow chimeras 608 radioimmunodiffusion
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lymphoid tissues and recirculating lymphocytes. Small doses
of radiation can lead to programmed cell death (apoptosis) of
lymphocytes and myeloid progenitor cells. Immune system
sensitivity to radiation is characterized by (1) the magnitude
of the suppression of the primary or secondary immune
response, (2) the reduction in size of lymphoid organs, and
(3) the diminished number of surviving lymphoid cells.
Whereas lymphoid cells are very radiosensitive, selected
radioresistant immune functions (and cells) are maintained
after significant doses of radiation. The effects of radiation
on immunity do not depend on their actions on lymphocytes
alone but also on the leukocytes that mediate nonspecific
host responses. Microphages and other nondividing cells
are relatively radioresistant. They may even be activated
following irradiation, revealing enhanced RNA synthesis,
enhanced production of cytokines, and increased synthesis
and release of lysosomal enzymes. Polymorphonuclear
neutrophilic leukocyte phagocytic ability is not decreased
by radiation, which may even increase intracellular killing
of phagocytized microorganisms. Most mature resting lymphocytes
are killed by 80 to 500 rad within hours following
radiation. Lymphocytes stimulated by mitogen or antigen
become more radioresistant and maintain their functions
and viability even following 1000 rad. The thymus is the
most radiosensitive lymphoid organ. Radiation is usually
more harmful to the antibody response than to delayed-type
hypersensitivity (DTH) responses. The irradiation of mice
(440 rad) just before antigen exposure leads to immune suppression,
whereas the same dose of irradiation 4 days after
antigenic challenge leads to increased antibody titers. The
in vivo secondary immune response is more radioresistant
Wells cut
into gel for
placement
of soluble
antigen
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Agarose gel with
antibody throughout
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Radioimmunodiffusion.
Antigen diffuses,
a circular concentration
gradient is produced
Radioimmunodiffusion.
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mg/100 ml
150 200
49 66 93 146 185
mg/100 ml
than the primary response. DTH is relatively radioresistant
in comparison to antibody production. Most cytotoxic T
lymphocytes are radioresistant to doses of several thousand
rad. Many immunodeficient conditions have been associated
with increased sensitivity to radiation.
radiation bone marrow chimeras
Mice subjected to heavy radiation and then reconstituted
with allogeneic bone marrow cells (from a different mouse
strain). Thus, their lymphocytes are genetically different
from the surroundings in which they develop. These chimeric
mice have yielded significant data in the investigation of
lymphocyte development.
radiation chimera
Refer to irradiation chimera.
radiation therapy
The destruction of tumor cells by ionizing radiation administered
externally as a focused beam or as brachytherapy.
radioallergosorbent test
Refer to RAST.
radioimmunoassay (RIA)
A binder ligand technique used to assay antigen or antibody;
it is based on competitive inhibition by a radiolabeled antigen
of the binding of an unlabeled antigen to specific antibodies.
Minute quantities of enzymes, hormones, and other immunogenic
substances can be assayed by RIA. Enzyme immunoassays
have largely replaced RIAs because of the problems
associated with radioisotope regulation and disposal.
radioimmunodiffusion
A variation of the immunodiffusion technique that uses a
radioactively labeled antibody. This enhances the sensitivity
Precipitin rings form,
antigen concentration is
related to size to ring