Background: The trans vivo delayed-type hypersensitivity (DTH) assay has been used for monitoring the immune status of clinical transplant recipients. Here we tested the hypothesis that the assay can reveal control of allograft rejection by CD25CD4 regulatory T cells (Treg).
Methods: CBA.Ca (H2) recipients of heterotopic C57BL/10 (H2, B10) heart transplants were untreated or pretreated with anti-CD4 antibody and donor-specific blood. This protocol has been shown previously to induce operational tolerance to alloantigens that is dependent on CD25CD4 Treg. Four weeks after transplantation leukocytes were harvested and used for the trans vivo DTH assay. Cells were stimulated with irradiated B10 leukocytes or subcellular antigen and injected into ear pinnae of immune deficient CB17.SCID.beige hosts.
Results: Stimulation of leukocytes from recipients rejecting B10 cardiac allografts with recall alloantigen caused a "strong" swelling response, whereas similar stimulation of leukocytes from operationally tolerant mice resulted in significantly less swelling (n=17; P=0.003). When CD25 T cells were depleted from "tolerant" leukocytes, the swelling response triggered was similar to that obtained using cells from rejecting animals (P<0.001), while coinjection of purified CD25CD4 cells from tolerant recipients with rejecting cells suppressed the swelling response (P=0.007) to the level observed with cells from tolerant mice. Both the effector and the regulatory response were triggered by indirect allorecognition and blocking experiments showed that the regulation observed was dependent on cytoxic T lymphocyte antigen (CTLA) 4.
Conclusion: The trans vivo DTH assay can be used to reveal regulation mediated by CD25CD4 T cells and is CTLA4 dependent.