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histamine-releasing factor 327 histocompatibility locus
histamine-releasing factor
A lymphokine produced from antigen-stimulated lymphocytes
that induces the release of histamine from basophils.
histiocyte
A tissue macrophage that is fixed in the tissues such as
connective tissues. Histiocytes are frequently found around
blood vessels and are actively phagocytic. They may be
derived from monocytes in the circulating blood.
histiocytic lymphoma
A misnomer for large cell lymphomas, principally B cell
tumors. The term histiocytic lymphoma more accurately
describes a lymphoma of macrophage lineage.
histiocytosis X
A descriptor for neoplasms of macrophage lineage. Included
in this category are Letterer–Siwe disease, Hand–Schüller–
Christian disease, and eosinophilic granuloma of bone.
DR
DQ
DP
Human chromosome 6.
histocompatibility
Tissue compatibility, as in the transplantation of tissues or
organs from one member to another of the same species
(allograft) or from one species to another (xenograft). The
genes that encode antigens that should match if a tissue or
organ graft is to survive in a recipient are located in the major
histocompatibility complex (MHC) region on the short arm
of chromosome 6 in humans and on chromosome 17 in mice.
MHC class I and class II antigens are important in tissue transplantation.
The greater the match between donor and recipient,
the more likely a transplant is to survive. For example, a
six-antigen match implies sharing of two HLA-A antigens, two
HLA-B antigens, and two HLA-DR antigens between donor
and recipient. Even though antigenically dissimilar grafts may
survive when a powerful immunosuppressive drug such as
cyclosporine is used, the longevity of the graft is still improved
by having as many antigens match as possible.
histocompatibility antigen
One of a group of genetically encoded antigens present on
tissue cells that provoke a rejection response if the tissue
containing them is transplanted to a genetically dissimilar
recipient. These antigens are detected by typing lymphocytes
on which they are expressed. They are encoded in
humans by genes at the human leukocyte antigen (HLA)
locus on the short arm of chromosome 6. In mice, they are
encoded by genes at the H-2 locus on chromosome 17.
A
C
B
B3
B3
B1
A1
B1
A1
B1
Centromere
Hand-mirror cell.
Schematic representation of the three-dimensional structure of the
external domains of a human class I HLA molecule based on x-ray
crystallographic analysis. The β strands are depicted as thick arrows
and the α helices as spiral ribbons. Disulfide bonds are shown as two
interconnected spheres. The α 1 and α 2 domains interact to form the
peptide-binding cleft. Note the immunoglobulin-fold structure of the α 3
and α 2 microglobulin.
histocompatibility locus
The specific site on a chromosome where the histocompatibility
genes that encode histocompatibility antigens are
located. There are major histocompatibility loci such as
human leukocyte antigen (HLA) in humans and H-2 in
H