PART IV The Immune System in Health and Disease First skin graft, First-set rejection Second-set rejection Necrosis Time 6 days Naive strain=B mouse Spleenic T cells Second-setrejection strain A k Naive strain= B mouse FIGURE 21.2 Experimental demonstration that T cells can trans- ent mounts a second-set rejection to an initial allograft from the orig- fer allograft rejection. When T cells derived from an allograft-primed inal allogeneic strain mouse are transferred to an unprimed syngeneic mouse, the recipi gives a high probability of heterozygosity at most loci In mat- Graft Donors and Recipients Are Typed ings between members of an outbred species, there is only a for RBC and MHC Antigens 25% chance that any two offspring will inherit identical MHC haplotypes(see Figure 7-2c), unless the parents share one or Since differences in blood group and major histocompatibility more haplotypes. Therefore, for purposes of organ or bone- antigens are responsible for the most intense graft-rejection marrow grafts, it can be assumed that there is a 25% chance of reactions, various tissue-typing procedures to identify these ity within the MHc bet With parent-to- antigens have been developed to screen potential donor and child grafts, the donor and recipient will always have one hap- recipient cells. Initially, donor and recipient are screened for lotype in common but are nearly always mismatched for the ABO blood-group compatibility. The blood-group antigens haplotype inherited from the other parent. are expressed on RBCs, epithelial cells, and endothelial cells Antibodies produced in the recipient to any of these antigens that are present on transplanted tissue will induce antibody- mediated complement lysis of the incompatible donor cells HLa typing of potential donors and a recipient can be accomplished with a microcytotoxicity test(Figure 21-4a, b) In this test, white blood cells from the potential donors and 50FAnti- recipient are distributed into a series of wells on a microtiter ntrol Anti-CD4 Anti-CD4 CD8 and Anti-CD8 plate, and then antibodies specific for various class I and class II MHC alleles are added to different wells. After incubation, complement is added to the wells, and cytotoxicity is by the uptake or exclusion of various dyes(e.g, trypan blue Time after grafting, days or eosin y) by the cells. If the white blood cells express the MHC allele for which a particular monoclonal antibody is GURE21-3 The role of CD4*and CD8 T cells in allograft rejec- specific, then the cells will be lysed upon addition of comple tion is demonstrated by the curves showing survival times of skin ment, and these dead cells will take up a dye such as trypa grafts between mice mismatched at the MHC. Animals in which the blue. hla typing based on antibody-mediated microcyto- CD8 T cells were removed by treatment with an anti-CD8 mono- toxicity can thus indicate the presence or absence of various clonal antibody (red) showed little difference from untreated control MHC alleles. mice(black). Treatment with monoclonal anti-CD4 (blue)improved Even when a fully HLa-compatible donor is not available graft survival significantly, and treatment with both anti-CD4 and transplantation may be successful. In this situation, a one-way anti-CD8 antibody prolonged graft survival most dramatically mixed-lymphocyte reaction(MLR)can be used to quantif (green). /Adapted from S P. Cobbold et al., 1986, Nature 323: 165. the degree of class II MHC compatibility between potentialgives a high probability of heterozygosity at most loci. In mat￾ings between members of an outbred species, there is only a 25% chance that any two offspring will inherit identical MHC haplotypes (see Figure 7-2c), unless the parents share one or more haplotypes. Therefore, for purposes of organ or bone￾marrow grafts, it can be assumed that there is a 25% chance of identity within the MHC between siblings. With parent-to￾child grafts, the donor and recipient will always have one hap￾lotype in common but are nearly always mismatched for the haplotype inherited from the other parent. Graft Donors and Recipients Are Typed for RBC and MHC Antigens Since differences in blood group and major histocompatibility antigens are responsible for the most intense graft-rejection reactions, various tissue-typing procedures to identify these antigens have been developed to screen potential donor and recipient cells. Initially, donor and recipient are screened for ABO blood-group compatibility. The blood-group antigens are expressed on RBCs, epithelial cells, and endothelial cells. Antibodies produced in the recipient to any of these antigens that are present on transplanted tissue will induce antibody￾mediated complement lysis of the incompatible donor cells. HLA typing of potential donors and a recipient can be accomplished with a microcytotoxicity test (Figure 21-4a, b). In this test, white blood cells from the potential donors and recipient are distributed into a series of wells on a microtiter plate, and then antibodies specific for various class I and class II MHC alleles are added to different wells. After incubation, complement is added to the wells, and cytotoxicity is assessed by the uptake or exclusion of various dyes (e.g., trypan blue or eosin Y) by the cells. If the white blood cells express the MHC allele for which a particular monoclonal antibody is specific, then the cells will be lysed upon addition of comple￾ment, and these dead cells will take up a dye such as trypan blue. HLA typing based on antibody-mediated microcyto￾toxicity can thus indicate the presence or absence of various MHC alleles. Even when a fully HLA-compatible donor is not available, transplantation may be successful. In this situation, a one-way mixed-lymphocyte reaction (MLR) can be used to quantify the degree of class II MHC compatibility between potential 484 PART IV The Immune System in Health and Disease First skin graft, strain A Second skin graft, strain A Naive strain = B mouse First-set rejection Second-set rejection 14 days Time 6 days Naive strain = B mouse Necrosis First skin graft, strain A Necrosis Second-set rejection 6 days Necrosis Spleenic T cells FIGURE 21-2 Experimental demonstration that T cells can trans￾fer allograft rejection. When T cells derived from an allograft-primed mouse are transferred to an unprimed syngeneic mouse, the recipi￾ent mounts a second-set rejection to an initial allograft from the orig￾inal allogeneic strain. Surviving grafts, % Time after grafting, days 50 100 15 30 60 0 Anti– Control Anti–CD4 CD8 Anti–CD4 and Anti–CD8 FIGURE 21-3 The role of CD4+ and CD8+ T cells in allograft rejec￾tion is demonstrated by the curves showing survival times of skin grafts between mice mismatched at the MHC. Animals in which the CD8+ T cells were removed by treatment with an anti-CD8 mono￾clonal antibody (red) showed little difference from untreated control mice (black). Treatment with monoclonal anti-CD4 (blue) improved graft survival significantly, and treatment with both anti-CD4 and anti-CD8 antibody prolonged graft survival most dramatically (green). [Adapted from S. P. Cobbold et al., 1986, Nature 323:165.]