Page 547 - Review of Medical Microbiology and Immunology ( PDFDrive )

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Complex & Transplantation 62
R
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Major Histocompatibility

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CHAPTER C ONTENT S

HLA Typing in the Laboratory
Introduction
MHC Proteins
The Fetus Is an Allograft That Is Not Rejected
Results of Organ Transplants
Class I MHC Proteins
Graft-Versus-Host Reaction
Class II MHC Proteins
Biologic Importance of MHC
Self-Assessment Questions
Transplantation
Practice Questions: USMLE & Course Examinations
Allograft Rejection
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INTRODUCTION
Each person has two haplotypes (i.e., two sets of these
The success of tissue and organ transplants depends on
chromosome 6). These genes are very diverse (polymor-
the donor’s and recipient’s human leukocyte antigens
phic) (i.e., there are many alleles of the class I and class II
(HLA) encoded by the HLA genes. These proteins are
genes). For example, there are at least 47 HLA-A genes, 88
alloantigens (i.e., they differ among members of the same
HLA-B genes, 29 HLA-C genes, and more than 300 HLA-D
species). If the HLA proteins on the donor’s cells differ
genes, but any individual inherits only a single allele at each
from those on the recipient’s cells, then an immune
response occurs in the recipient. The genes for the HLA
two class I and II proteins at each gene locus. Expression of
proteins are clustered in the major histocompatibility
these genes is codominant (i.e., the proteins encoded by
complex (MHC), located on the short arm of chromosome 6. locus from each parent and thus can make no more than
both the paternal and maternal genes are produced). Each
Three of these genes (HLA-A, HLA-B, and HLA-C) code
person can make as many as 12 different HLA proteins: 3
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for the class I MHC proteins. Several HLA-D loci deter-
at class I loci and 3 at class II loci, from both chromosomes.
mine the class II MHC proteins (i.e., DP, DQ, and DR)
A person can make fewer than 12 different HLA proteins if
(Figure 62–1). The features of class I and class II MHC
proteins are compared in Table 62–1.
parents have the same HLA allele).
Pg5
L
O HLA
D
C2, C4, B C A
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DP
TNF, LT
DQ
DR
Class II
Class III
Class I
FIGURE 62–1
The human leukocyte antigen (HLA)–gene complex. A, B, and C are class I loci. DP, DQ, and DR are class II loci. C2 and C4
are complement loci. LT, lymphotoxin; TNF, tumor necrosis factor. PGM 3 , GLO, and Pg5 are adjacent, unrelated genes. (Reproduced with permission
from Stites DP, Terr A, Parslow T, eds. Basic & Clinical Immunology. 9th ed. Originally published by Appleton & Lange. Copyright 1997 McGraw-Hill.)
536

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