First set rejection

FIGURE 16-2 First- and second-set allograft rejection. Results of the experiments shown indicate that graft rejection displays the features of adaptive immune responses, namely, memory and mediation by lymphocytes. An inbred strain B mouse will reject a graft from an inbred strain A mouse with first-set kinetics (left panel). An inbred strain B mouse sensitized by a previous graft from an inbred strain A mouse will reject a second graft from an inbred strain A mouse with second-set kinetics (middle panel), demonstrating memory. An inbred strain B mouse injected with lymphocytes from another strain B mouse that has rejected a graft from a strain A mouse will reject a graft from a strain A mouse with second-set kinetics (rightpanel), demonstrating the role of lymphocytes in mediating rejection and memory. An inbred strain B mouse sensitized by a previous graft from a strain A mouse will reject a graft from a third unrelated strain with first-set kinetics, thus demonstrating another feature of adaptive immunity, specificity (not shown). Syngeneic grafts are never rejected (not shown).

• Cells or organs transplanted between genetically identical individuals (identical twins or members of the same inbred strain of animals) are never rejected.

• Cells or organs transplanted between genetically non-identical people or members of two different inbred strains of a species are almost always rejected.

• The offspring of a mating between two different inbred strains of animal will typically not reject grafts from either parent. In other words, an (A x B)F1 animal will not reject grafts from an A or B strain animal. (This rule is violated by bone marrow transplantation, which we will discuss later in the chapter.)

• A graft derived from the offspring of a mating between two different inbred strains will almost always be rejected by either parent. In other words, a graft from an (A x B)F1 animal will be rejected by either an A or a B strain animal.

Such results suggested that the molecules in the grafts that are responsible for eliciting rejection must be polymorphic and their expression is codominant. Polymorphic refers to the fact that these graft antigens differ among the individuals of a species (other than identical twins) or between different inbred strains of animals. Codominant expression means that every individual inherits genes encoding these molecules from both parents and both parental alleles are expressed. Therefore, (A x B)F1 animals express both A and B alleles

Donor (Strain A)

Donor (Strain B)

Donor (Strain B)

Donor (Strain A x B)

Graft rejection

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