Regulatory cell-mediated tolerance does not protect against chronic rejection.

Area of Science:

• Immunology
• Transplantation Biology
• Cellular Immunology

Background:

• Regulatory cells are crucial for preventing acute graft rejection and inducing immune tolerance.
• Th2 cytokines, stimulated by regulatory cells, can promote alloantibody production, leading to chronic rejection.
• The protective role of regulatory cell-mediated tolerance against chronic rejection remains unclear.

Purpose of the Study:

• To investigate whether regulatory cell-mediated tolerance protects against chronic rejection after heart transplantation.
• To determine the immunological mechanisms underlying chronic rejection in tolerant recipients.

Main Methods:

• Rat heart transplantation (Htx) models using different strains (RA and PVG).
• Donor-specific blood transfusion (DSBT) to induce tolerance.
• Transfer of splenocytes from tolerant rats to assess regulatory cell function.
• Analysis of vascular occlusion, intragraft cytokine production (Th1/Th2), graft infiltrate, and immunoglobulin/complement deposition.

Main Results:

• Donor-specific blood transfusion (DSBT) induced long-term acceptance of primary and secondary grafts, indicating successful tolerance induction.
• Tolerant recipients, despite accepting grafts, showed significant features of chronic rejection, including vascular occlusion (VO).
• A Th2 deviation, characterized by increased interleukin-4 (IL-4) production, was observed in grafts, correlating with B cell infiltration and IgG1/C3 deposition.

Conclusions:

• Regulatory cells effectively prevent acute graft rejection and ensure acceptance of both primary and secondary allografts.
• Despite preventing acute rejection, regulatory cell-mediated tolerance does not prevent the development of chronic rejection.
• The findings suggest that Th2-biased immune responses and antibody production contribute to chronic rejection even in the presence of tolerance.