Immunopathology of antibodies as effectors of orthotopic liver allograft rejection

Direct allorecognition promotes activation of bystander dendritic cells and licenses them for Th1 priming: a functional link between direct and indirect allosensitization

T-cell sensitization to indirectly presented alloantigens (indirect pathway of allorecognition) plays a critical role in chronic rejection. The usual very efficient priming of such self-restricted, T helper type 1 (Th1)-deviated CD4+ T cells obviously conflicts with the fact that allogeneic MHC molecules are poorly immunogenic per se. The aim of the present study is to elucidate whether direct allosensitization induces production of inflammatory mediators that may affect recruitment and activation of immature bystander (host) dendritic cells (DC). These potential mechanisms were studied in vitro by conducting primary allogeneic mixed leucocyte reactions (MLR), mimicking the priming phase in secondary lymphoid organs, and secondary MLR, mimicking the effector phase within the graft. Primary, and particularly secondary, MLR supernatants were found to contain high levels of monocyte/immature DC-recruiting CC chemokines and pro-inflammatory cytokines. Exposure of immature DC to primary or secondary MLR supernatants was found to upregulate CD40 expression and further enhanced lipopolysaccharide-induced interleukin-12 (IL-12) p70 production. Secondary MLR supernatants additionally induced upregulation of CD86 and deviated allogeneic T-cell responses towards Th1 (enhanced interferon-gamma production without concomitant induction of detectable IL-4 or IL-10 production). These findings indicate that direct allorecognition may act as a Th1-deviating adjuvant for indirect allosensitization.

The role of B cells and alloantibody in the host response to human organ allografts

Some human organ transplants deteriorate slowly over a period of years, often developing characteristic syndromes: transplant glomerulopathy (TG) in kidneys, bronchiolitis obliterans in lungs, and coronary artery disease in hearts. In the past, we attributed late graft deterioration to "chronic rejection", a distinct but mysterious immunologic process different from conventional rejection. However, it is likely that much of chronic rejection is explained by conventional T-cell-mediated rejection (TMR), antibody-mediated rejection (AMR), and other insults. Recently, criteria have emerged to now permit us to diagnose AMR in kidney transplants, particularly C4d deposition in peritubular capillaries and circulating antibody against donor human leukocyte antigens (HLA). Some cases with AMR develop TG, although the relationship of TG to AMR is complex. Thus, a specific diagnosis of AMR in kidney can now be made, based on graft damage, C4d deposition, and donor-specific alloantibodies. Criteria for AMR in other organs must be defined. Not all late rejections are AMR; some deteriorating organs probably have smoldering TMR. The diagnosis of late ongoing AMR raises the possibility of treatment to suppress the alloantibody, but efficacy of the available treatments requires further study.

Positive T lymphocytotoxic cross-match in living donor liver transplantation

The influence of lymphocytotoxic cross-match on survival or acute rejection in living donor liver transplantation (LDLT) has not been well examined. We analyzed 133 consecutive adult LDLT cases and assessed patient survival and acute rejection rates. Patients with a positive T lymphocytotoxic cross-match (n = 12) had a significantly higher chance of rejection within 6 weeks of LDLT (67% versus 28%, P <.001). All of the rejection episodes were successfully treated with bolus methylprednisolone therapy or anti-T cell monoclonal antibody. T lymphocytotoxic cross-match-positive grafts had no influence on patient survival (79% versus 90% at 3 years, P =.91). The results show that a positive cross-match graft should not be considered a contraindication for LDLT.

Is presensitization relevant to liver transplantation outcome?

The impact of anti-HLA antibodies and crossmatch (CM) on liver transplantation (LT) outcome is still controversial. In this retrospective study we analyzed LT outcome according to pretransplant pre-formed anti-HLA antibodies and CM status. Serum anti-HLA antibodies were screened by ELISA assay, utilizing One Lambda antigen tray-mixed (LAT-M). CMs were performed by the complement dependent cytotoxicity test using Dithiotreitol treated sera. Anti-HLA antibodies were studied in 80 recipients; 56/80 had positive LAT-M tests (PLAT-M), whereas the remaining 24 recipients tested negative for both classes I and II (NLAT-M). Rejection episodes were more frequent in PLAT-M compared with NLAT-M group in post-LT intervals of <1 week (p = 0.05), 1 week-3 months (p = 0.035), and 3-12 months (p = 0.076). Graft and patient survival rates were better, albeit not significantly, in the NLAT-M compared with PLAT-M recipients. CM status was investigated in 62/80 recipients, 18/62 recipients had positive CM (PCM), and 44 had negative CM (NCM). Five of 18 PCM recipients (28%) experienced early graft loss compared with 1/44 (2%) with NCM (p = 0.006). Rejection episodes were more frequent within first 3 months post-LT in PCM recipients compared with NCM (p = 0.015). One-year graft survival rate was better in NCM, compared with PCM recipients (graft loss of 2/44 vs 5/18). NCM PLAT-M had a higher incidence of rejection episodes compared with the NCM NLAT-M group (p = 0.031). The presence of anti-HLA antibodies suggests a deleterious effect on LT outcome, and was associated with an increased incidence of early graft loss and rejection episodes.

SIGNIFICANCE OF A T-LYMPHOCYTOTOXIC CROSSMATCH IN LIVER AND COMBINED LIVER-KIDNEY TRANSPLANTATION

BACKGROUND

In contrast to kidney transplants a positive crossmatch is no contraindication for liver transplantation (OLT). In liver transplantation, antibody mediated rejections are rarely reported and a liver graft is suspected to have protective effects for kidney grafts when transplanted simultaneously. The aim of this study was to evaluate the effect of a positive crossmatch on outcome after OLT and combined liver and kidney transplantation (CLKTx).

METHODS

We analyzed retrospectively the impact of a positive crossmatch on graft survival and rejection episodes after OLT (793pats) and CLKTx (18pats, 2.2%). Immunosuppression consisted of either Cyclosporine- or Tacrolimus-based regimens.

RESULTS

A total of 50/811 (6%) of patients had a positive crossmatch, 45/793 (5.6%) with liver transplantation alone and 5/18 (28%) of patients with CLKTx. Follow-up ranged from 1 to 122.5 months (median 45.8 months). One- and 5-year graft survival rates of liver transplants alone with a positive crossmatch were 89.6% and 75.3%, respectively and were 88% and 77.5% in crossmatch negative recipients. Additionally, the incidence of acute and steroid-resistant rejection (44% and 15.5%) was not significantly increased in patients with a positive crossmatch when compared with patients with a negative crossmatch (38% and 19%). None of the patients with a positive crossmatch and CLKTx underwent a hyperacute-rejection episode after transplantation, and kidney graft survival 100%.

CONCLUSIONS

In conclusion, a positive crossmatch is no contraindication for OLT and CLKTx. Furthermore, not having to wait for results of donor/recipient crossmatching can shorten cold ischemia time and may improve the clinical outcome.

Early recipient-donor switch of the complement type after liver xenotransplantation

Liver transplantation is an immunological peculiarity with respect to the resistance of the graft to humoral rejection. We undertook a kinetic analysis of molecules involved in humoral rejection for a period of one week following xenografting in the hamster to rat model system. A complement-dependent lymphocytotoxicity test (CDC) was used to detect anti-donor antibodies in the recipient rats. Complement was studied by two methods. Function of the classical complement pathway was evaluated with a hemolytic assay, and C3 was measured by radial immunodiffusion. Conversion of the major plasma proteins from recipient to donor profile was studied by zone electrophoresis on agarose. CDC showed antibody titers rose during the first week post-transplantation, and they were of complement-activating isotypes. Zone electrophoresis showed almost complete replacement of rat C3 by hamster C3 within 72 hours. Hemolytic assay of complement on day 6 post-transplant showed serum of the xenograft recipients could lyse erythrocytes sensitized with rat antibody with 80% of efficiency of normal rat serum. Our data show the effector molecules for humoral rejection, rat antibodies with anti-hamster specificity and a functional complement cascade, were present within the first week following transplantation. Rapid conversion of serum complement to hamster proteins maintains compatibility with the species-specific membrane inhibitors of complement activation expressed by the xenografted hepatocytes, and could limit complement-mediated damage.

Centrilobular necrosis after orthotopic liver transplantation: a longitudinal clinicopathologic study in 71 patients

Centrilobular necrosis (CLN) is a histological finding often encountered after orthotopic liver transplantation, but its pathogenesis is still unknown. In this study, the significance of CLN was assessed in a series of 227 consecutive liver transplantations performed between January 1989, and December 1991. Seventy-one patients (30.9%) showed CLN on at least one biopsy result, which were obtained because of an increase of aspartate aminotransferase activity. Their liver specimens were reviewed, and 19 histological features were recorded with particular attention given to lobular changes in acinar zone 3, to features commonly attributed to cellular and ductopenic rejection, and to changes suggestive of ischemia. CLN could first be observed either soon (within 4 days) or late (up to 3 years) after transplantation. Only 23 (32.4%) specimens had centrilobular necrosis affecting more than 75% of acinar zones 3. In 60 cases (84.5%) the lesion was limited to acinar zone 3. An important associated feature was sinusoidal congestion in 73.2% of cases. Fifty-one of 71 patients (71.8%) had histological features of cellular rejection before or at the time of CLN, and 13 of these progressed to ductopenic rejection versus 3 of the 156 patients without CLN (P < .0001). Nine patients had a recurrence of CLN, of whom 2 progressed to ductopenic rejection, a recurrence rate of 16.7% in this series. The survival of patients with CLN is worsened by associated ductopenic portal tracts compared with those without ductopenia (P = .0189-Mantel-Cox). This histological combination, irrespective of the serum bilirubin level, may warrant an early conversion to FK506-based immunosuppression.

Immunoglobulin G lymphocytotoxic antibodies in clinical liver transplantation: studies toward further defining their significance

Twenty-two consecutive liver allograft recipients, who tested positive for immunoglobulin G (IgG) lymphocytotoxicity were subjected to pretransplantation and posttransplantation immunologic monitoring of anti-donor IgG lymphocytotoxic antibody titers, total hemolytic complement activity (CH100), circulating immune complexes (CIC), and platelet counts in an effort to improve our understanding of the preformed antibody state in clinical hepatic transplantation. Ten contemporaneous liver transplant recipients whose crossmatch results were negative and who experienced severe hepatocellular damage early after transplantation were included as controls. Crossmatch test results were negative 1 day after transplantation and during the 1 month follow-up remained negative in 14 of 22 (64%) sensitized recipients, most of whom had relatively low (< or = 1:16) anti-donor IgG antibody titers before transplantation. After transplantation, this group and the control group experienced no thrombocytopenia, no increase of CIC, and a gradual increase in CH100 activity that reached normal levels within 1 week. A strong negative correlation between prothrombin time (PT) and CH100 activity in these groups of patients suggested that changes in CH100 activity (P < .0005) were tightly linked to liver synthetic function. In contrast, the crossmatch test results remained positive after transplantation in 8 of 22 (36%) sensitized recipients, all of whom had relatively high (> 1:32 to 1024) pretransplantation titers of anti-donor IgG antibodies. After transplantation these patients developed a syndrome that was characterized by decreased CH100 activity and increased CIC compared with pretransplantation levels and refractory thrombocytopenia that was associated with a 50% allograft failure rate because of biopsy-proven humoral and acute (cellular) rejection.(ABSTRACT TRUNCATED AT 250 WORDS)