When researchers reversed the transplant, however—putting islets expressing IL-4 into diabetic mice—the grafts were rejected. The beta cells in the transplanted islets were destroyed, while the alpha cells remained stupidly in the graft. This suggests that, once autoreactivity develops, you cannot stop committed or primed cells from killing the islet.
On the other hand, when researchers transplanted splenocytes from NOD diabetic mice into an NOD IL-4 transgenic recipient, they again saw protection, while disease was transferred when splenocytes were transplanted to NOD controls. Researchers recognize that these are contradictory results and suggest that the difference has to do with the “audience.” That is, circulating cells have a much higher proportion of primed, or memory cells, whereas the spleen contains both primed and unprimed, memory and naive cells; the presence of at least some naive cells in the tissue being transferred allows for some regulation. Researchers are currently testing this hypothesis.
These results suggest that the immune system must see antigen in order to produce tolerance, but only if it is seen in the presence of IL-4. If the antigen is seen alone, the result is destruction, and seeing it a second time in the presence of IL-4 doesn’t seem to give any kind of regulation. They also suggest that the T-cells enter the islet naive, and that priming occurs within the islet. This in turn suggests that therapy could be accomplished locally if it were possible to “speak” to the cells as they entered the islet. This could be done more elegantly if it were possible to merely add the proper determinants, but this will require a better understanding of natural Th-2 determinants, conditions for priming, site of priming, cytokines, etc.
In response to questions from the audience, Dr. Sarvetnick added the following:
The IL-4 in these experiments was murine IL-4, so this could not be the reason for the rejection.
An IL-4-producing islet from a BALB/c donor is not rejected when transplanted into a BALB/c recipient, only by an NOD recipient.
The results with TGF-beta are far less interesting—essentially a fibrosis of the pancreas without any sign of blocking diabetes, at least in their lab. Other researchers have found some signs of inhibition.
Researchers have not looked at the pattern of B-cell development or how it is altered in transgenic mice, except with regard to IFN-gamma. B7–1 and B7– 2 are in the infiltrates in the NOD mouse, but they have not looked at whether that is down-regulated. It would be a good experiment.
Slides of the islets of transgenic mice show lymphocytes surrounding but not infiltrating the islets. This suggests that the protective effect of IL-4 may come from altering the receptors or adhesion molecules on lymphocytes.
Researchers have not looked at endothelial markers extensively.