Tolerant mouse T cells are depleted 4 6 weeks after lymphocyte transfer

Figure E1.3. Demonstration of infectious tolerance. This requires the demonstration that cells with the ability to reject are converted into the regulatory type after coexistence with cells from a tolerant animal.

graft from a similar donor, but they could now regulate another population of spleen cells from a non-tolerant animal in a similar transfer experiment.7 This effect, named "infectious tolerance", provides compelling evidence for the existence of regulatory T cells: the regulatory cells from a tolerant animal can suppress the aggressive action of graft-reactive T-cells and induce members of that population to become regulatory as well.

A further important finding underlining the significance of infectious tolerance comes from the demonstration of a phenomenon named "linked suppression". In the original experiment27 mice of type A made tolerant to type B skin grafts with non-depleting anti-CD4 and anti-CD8 treatment, readily rejected a third party graft of type C. However, if they were grafted with (BxC)F1 skin instead, rejection was delayed or absent while (AxC)F1 grafts were readily rejected. Furthermore, mice that accepted the (BxC)F1 skin grafts later accepted C type skin. The same phenomenon was recently demonstrated for anti-CD40L antibody induced tolerance.28

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