T lymphocyte indifference to extrathymic islet allografts

Area of Science:

• Immunology
• Transplantation Biology
• T cell tolerance

Background:

• Tolerance to self-antigens in the thymus is well-established.
• Mechanisms of tolerance to antigens in peripheral tissues are less understood.
• Previous studies on peripheral antigen expression yielded varied results on T cell tolerance.

Purpose of the Study:

• To investigate if extrathymic tissue allografts can induce a developmental form of tolerance.
• To determine the T cell response to peripheral alloantigens in the absence of donor antigen-presenting cells.
• To clarify the relationship between transgenic models of tolerance and transplantation tolerance.

Main Methods:

• Utilized pancreatic islet allografts as a model for extrathymic alloantigen expression in severe combined immune-deficient (SCID) mice.
• Depleted donor antigen-presenting cells (APCs) from allografts.
• Adoptively transferred bone marrow-derived T cell precursors and assessed their reactivity in vitro and in vivo.

Main Results:

• T cell precursors maturing with peripheral islet allografts showed no activation or tolerance.
• T cells were indifferent to extrathymic antigens presented without a second costimulatory signal.
• This suggests a lack of developmental tolerance induction by extrathymic tissue allografts.

Conclusions:

• Extrathymic tissue allografts, when devoid of donor APCs, do not induce T cell tolerance.
• The absence of costimulatory signals is critical for T cell engagement with peripheral antigens.
• Findings challenge the direct translation of transgenic tolerance models to transplantation tolerance