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germ-free animal 293 Gershon, Richard K. (1932–1983)
homozygous (transgene present on only one chromosome in
a pair) or wild type (transgene not present on either chromosome
in a pair). When referring to knockout mice, the correct
term is homozygous (and sometimes they are called null
mice).
germ-free animal
An animal such as a laboratory mouse raised under sterile
conditions so that it is free from exposure to microorganisms
and is not exposed to larger organisms. Germ-free animals
have decreased serum immunoglobulin and lymphoid tissues
that are not fully developed. Their diets may also be controlled
to avoid exposure to food antigens. Most difficult is the ability
to maintain a virus-free environment for these animals.
germline
Unaltered genetic material that is transmitted from one
generation to the next through gametes. An individual’s germline
genes are those present in the zygote from which it
arose. The term refers to non-rearranged genes rather than
those rearranged for the production of immunoglobulin or T
cell receptor (TCR) molecules.
germ theory of disease
The concept that pathogenic microorganisms including bacteria,
fungi, parasites, and viruses visible only with the aid of a
microscope or electron microscope cause specific diseases.
germline configuration
The arrangement of immunoglobulin and T cell receptor
genes in the DNA of germ cells and in almost all somatic
cells in which somatic recombination has not taken place.
germline diversity
The inheritance of multiple gene segments that encode
V domains of antigen receptors. This form of diversity is
distinguished from that generated during gene rearrangement
or following receptor gene expression that is generated
somatically.
germline diversity of antigen receptors
The inheritance of multiple gene segments that encode
V domains. This is in contrast to the diversity arising from
gene rearrangement or following receptor gene expression,
which is somatically generated.
germline organization
The inherited arrangement of variable, diversity, joining,
and constant region gene segments of antigen receptor loci
in nonlymphoid cells or in immature lymphocytes. The
germline organization in developing T or B lymphocytes
is modified by somatic recombination to form functional
immunoglobulin or T cell receptor genes.
germline theory
A concept to explain antibody diversity by postulating that
each antibody is encoded in a separate germline gene.
germinal center
Germinal (or follicular) centers in lymph node and lymphoid
aggregates within primary follicles of lymphoid
tissues following antigenic stimulation. A germinal center
is a site of intense B cell proliferation, selection, maturation,
and death in secondary lymphoid tissue. Germinal
centers develop around follicular dendritic cell networks
when activated B cells migrate into lymphoid follicles. The
mixed cell population in the germinal center is comprised
of B lymphoblasts (cleaved and transformed lymphocytes),
follicular dendritic cells, and numerous tingible bodycontaining
macrophages. Germinal centers seen in various
pathologic states include “burned out” germinal centers
Efferent
lymphatic
Medulla
Lymphoid
follicle with
germinal center
(B Cell Zone)
Germinal center.
Germinal center.
Subscapular
sinus
Cortex
Paracortical zone
(T Cell Zone)
Tingible body macrophages in germinal center.
Afferent
lymphatics
composed of accumulations of pale histiocytes and scattered
immunoblasts; “progressively transformed” center
that shows “starry sky” patterns containing epithelioid
histiocytes, dendritic reticulum cells, increased T lymphocytes,
and mantle zone lymphocytes; and “regressively
transformed” germinal centers that are relatively small,
have few lymphocytes, and reveal an onion-skin layering
of dendritic reticulum cells, vascular endothelial cells, and
fibroblasts. Germinal centers are sites of isotype switching,
somatic hypermutation and affinity maturation.
germinal follicle
Refer to germinal center.
Gershon, Richard K. (1932–1983)
One of the first to demonstrate the suppressor role of the T
cell. The suppressor T cell was described as a subpopulation
of lymphocytes that diminish or suppress antibody
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