Anti-idiotypic antibodies from highly sensitized patients stimulate B cells to produce anti-HLA antibodies

HLA class II-like antiidiotypic antibodies from highly sensitized patients inhibit T-cell alloresponses

The purpose of this study is to identify factors in the sera of highly sensitized (HS) patients (pts) that inhibit T-cell alloresponses. An in vitro assay was used to measure HLA class I and class II-like antiidiotypic antibodies (anti-ids). The stimulation index (SI) was used to measure PBL and T-cell responses to alloantigens. All HS sera (32 pts) and the IgG fraction inhibited PBL and CD4(+) T-cell responses to alloantigens. The SI with HS IgG was 7.9 +/- 1.7 as compared to 31.5 +/- 5.9 with normal IgG (p = 0.0003). In a subset of pts who were transiently sensitized, the SI was 6.6 +/- 1.0 with a high panel reactive antibody (PRA), but when their PRA was zero, the SI was 17.8 +/- 1.3 (p = 0.0000001). Anti-ids were found in 100% of 17 pts with a high PRA. The T-cell inhibitory factors reduced CD4(+) T-cell responses of HS pts to alloantigens in the presence of autologous anti-ids, were MHC restricted and were inactivated by in vitro generated antibodies to HLA class II-like anti-ids. The HLA class II-like anti-id IgG molecules bind to the TCR of CD4(+) T cells and may impair their ability to help in the downregulating antibody response to anti-ids.

Mechanisms of chronic allograft dysfunction

This review was designed to highlight new findings that have contributed to our knowledge of the pathogenesis of late graft dysfunction. Both immune and nonimmune causes contribute to its development. Specific contributors to late graft dysfunction have been recently recognized and are potential targets for new treatment options. The variables associated with late graft failure include donor age and tissue quality, brain death and other issues specific to the deceased donor, tissue injury secondary to organ preservation, alloimmune-mediated injury, and posttransplantation factors in the recipient, such as viral infections, hypertension, drug toxicity, and hyperlipidemia. One of the critical variables that is controllable is the total ischemic time; the longer the ischemic episode, the worse the long-term results of the transplant are. Another significant obstacle to long-term allograft survival is the MHC barrier. The roles of B cells and alloantibody as effectors of alloimmunity have been underestimated; emerging studies strongly suggest that previous sensitization and/or de novo donor-anti-human lymphocyte antigen (HLA) antibodies secondary to poor HLA matching portend a poor prognosis for allograft survival, even in the presence of chronic T-cell-specific immunosuppression.

Abnormal B-cell regulation in highly sensitized patients with sustained serum levels of antibody to HLA class I antigens

BACKGROUND

There are anti-idiotypes in the sera of highly sensitized (HS) patients that stimulate B cells to produce antibody to HLA class I antigens. The purpose of this study is to determine if there is an abnormality in B cell responses to these anti-idiotypes.

METHODS

Supernatants from normal and HS B cells exposed to either HLA-like anti-idiotypes or HS sera were tested for IgG and antibody to HLA class I antigens by ELISA and flow beads.

RESULTS

When stimulated with HS sera, HS B cells produced antibody to HLA class I antigens (in vitro) (12/12) but normal B cells did not (0/10) (P<0.0001). When HS B cells were stimulated with isolated HLA-like anti-idiotypes, they produced more total IgG in the supernatant (603+/-105 ng/ml vs. 293+/-30 ng/ml; P<0.01) and more IgG1 (67+/-5.3 ng/ml vs. 32.3+/-5.4 ng/ml; P<0.001) and more IgG3 (33.3+/-9.2 vs. 2.03+/-0.2 ng/ml; P<0.0001) than normal B cells. The proliferative response to HLA-like anti-idiotypes was 1285+/-115 cpm from normal B cells and 1020+/-445 from HS B cells (p=NS).

CONCLUSIONS

When exposed to HS sera, HS B cells produced antibody to HLA class I antigens and normal B cells did not. When exposed to isolated HLA-like anti-idiotypes, HS B cells produced more total IgG, primarily IgG1 and IgG3 with normal proliferation. This intrinsic abnormality in HS B cells permits antibody to HLA class I antigens to be produced and allows increased amounts of IgG1 and IgG3 to be secreted in the absence of an increase in proliferation.

Donor-Specific Antibodies in Allograft Rejection: Clinical and Experimental Data

The ability of donor-specific major histocompatibility complex alloantibodies to destroy a transplanted organ within minutes, the so-called hyperacute rejection phenomenon, has been known for a long time. It is a clear demonstration of the possible cytotoxic effect of antibodies. Apart from this particular situation, the role of antibodies in inducing acute or chronic allograft rejection remains controversial. Many clinical data have shown that transplant recipients capable of developing class I or class II anti-HLA antibodies experienced shorter survival periods than those who were not. This fact, in accordance with experimental data, only demonstrates that high antibody responders reject a transplant more easily than low responders. More interestingly, there is now increasing evidence that posttransplant appearance of donor-specific alloantibodies, and probably of alloreactive-induced autoantibodies, is strongly correlated with reduced graft survival rate, especially from chronic rejection. We demonstrated that donor-specific HLA antibodies can be found in more than 70% of transplanted kidneys with chronic allograft nephropathy, and that the intragraft presence of such antibodies is significantly correlated with high numbers of plasma cells on early biopsies and C4d deposits, a recognized marker of humoral rejection. It is likely that non-HLA antibodies also play a deleterious role in organ transplant outcome, particularly the heterogeneous group of anti-endothelial cells antibodies, anti-MIC antibodies, autoantibodies and some others with no recognized target. Convincing experimental data, especially using B cell and T cell deficient mice, strongly suggest that B cells and donor-specific antibodies are required for fully developed chronic allograft rejection. The role of antibodies in inducing the cascade of cytokines and growth factors leading to tissue lesions is of increasing interest since it is now possible to control B cell proliferation and antibody production.

The use of rituximab, anti-CD20 monoclonal antibody, in pediatric transplantation

Rituximab, chimeric anti-human CD-20, is approved for treatment of B-cell lymphoma in adults. It is being used experimentally in other various immune-related disease such as immune thrombocytopenic purpura, myasthenia gravis, and rheumatoid arthritis. In transplant recipients it is used for treatment of post-transplant lymphoproliferative disease, and prevention and treatment of acute rejection. There are few data on its use in children. This paper reviews the use of rituximab in these disease states and provides hypotheses for its mode of action.