Immunoregulatory Effects of Allogeneic Mixed Chimerism Induced by T-Cell Depleted, Nonmyeloablative Bone Marrow Transplantation on Chronic Inflammatory Arthritis and Autoimmunity Developed in Interleukin-1 Receptor Antagonist-Deficient Mice.

Objective: To investigate the immunoregulatory effects of allogeneic mixed chimerism induced by T-cell depleted, nonmyeloablative bone marrow transplantation (TCD-NMT) on chronic inflammatory arthritis and autoimmunity developed in interleukin-1 receptor antagonist-deficient (IL-1Ra^{−/ −}) mice.

Methods: IL-1Ra^{−/ −} mice (H-2k^d) were treated with anti-asialoGM1 Ab, TBI 500 cGy, and TCD-NMT from C57BL/6 mice (H-2k^b). Engraftment and chimerism were evaluated on peripheral blood (PB), lymph node, and spleen by multi-color flow cytometry. The severity of arthritis was evaluated by clinical score and histopathology. IgG₁ and IgG_2a subtype of anti-type II collagen (CII) were measured in PB samples. After T cells were stimulated with CII, ovalbumin, and phytohemagglutinin, T-cell proliferation response and cytokines production (INF-g, TNF-a, IL-10, and IL-17) in culture supernatant were assayed.

Results: All the transplanted IL-1Ra mice showed marked improvement of arthritis within 3 weeks after transplantation as well as successful induction of mixed chimerism. Mice in mixed chimerism showed higher level of anti-CII IgG₁ and lower level of anti-CII IgG_2a and weaker T cell proliferative response than in control groups, such as no-treatment and conditioning only without BM rescue. In mixed chimera, INF-g, TNF-a and IL-17 production from CII-stimulated T cells was significantly suppressed and IL-10 production was significantly increased as compared to the control groups.

Conclusion: These observations indicate that the introduction of allogeneic mixed chimerism has a strong immunoregulatroy potential to correct established chronic inflammatory arthritis and autoimmunity originating from dysregulated proinflammatory cytokine network.