The prevalence and natural history of untreated isolated central perivenulitis in adult allograft livers

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Abstract

Central perivenulitis (CP) in the allograft liver can be associated with portal-based acute cellular rejection and autoimmune hepatitis or can occur in isolation (isolated CP). Although several studies have demonstrated the significance of CP, the prevalence and natural history of untreated isolated CP have not been well studied. We examined 100 adult allograft liver recipients who had long-term follow-up, had routine protocol biopsies, and received no treatment for isolated CP. Isolated CP was identified in 28 (28%) patients. It occurred late at a mean of 658 days. Interestingly, patients with late isolated CP (defined as >3 months posttransplant) usually manifested only mildly to modestly elevated liver function tests. However, late isolated CP was associated with prior and subsequent allograft complications. Nearly all (94%) cases of late isolated CP occurred in patients who had early episodes of CP and/or acute cellular rejection. Of 13 patients who developed adverse outcomes in their allografts (zone 3 fibrosis in 10, de novo autoimmune hepatitis in 3, and ductopenia in 3), all experienced episodes of prior CP, and 12 (92%) had late CP; 1 patient required retransplant for chronic rejection, but all were alive within the last year. In summary, “transplant-associated” isolated CP occurs in 28% of adult patients, early CP is predictive of late CP, and late CP (often present as isolated CP) is associated with long-term liver injury in some patients. Liver Transpl 14:625–632, 2008. © 2008 AASLD.

Centrilobular or perivenular inflammation and associated centrilobular hepatocyte dropout/necrosis constitute a distinct histopathologic process that can occur in the allograft liver. The understanding of this form of centrilobular injury has evolved over the years, and over this time, numerous posttransplant processes have been postulated, including acute cellular rejection (ACR), hepatic ischemia, drug (azathioprine and tacrolimus) toxicity, chronic hepatitis [recurrent viral hepatitis C and de novo or recurrent autoimmune hepatitis (AIH)], and chronic rejection. Paralleling the numerous etiologies cited in the literature, several different names have been given to this entity, including “central perivenulitis” (CP), “central venulitis,” “centrilobular necroinflammation,” “centrilobular hepatitis,” “centrilobular alterations,” and “veno-occlusive disease.” In this study, we used the term “central perivenulitis” to emphasize the importance of chronic inflammation in and around the central vein, but centrilobular hepatocyte dropout/necrosis and hemorrhage often accompany the inflammation.

When centrilobular necrosis without inflammation is present early posttransplant, it is most often associated with preservation injury or a vascular insult. When chronic inflammatory cells are associated with the centrilobular necrosis early after transplant, this process (CP) is now widely accepted to represent a component of ACR, even if it occurs in isolation (isolated CP), given that other potential etiologies are excluded.1–6 CP can also occur late posttransplant and is a characteristic feature of late-onset ACR/early chronic rejection.6–9 The challenge is determining the significance of isolated CP and assigning late isolated CP to a specific etiology because it could represent an immune-mediated process resulting from late-onset ACR, chronic rejection, or recurrent/de novo AIH.

Regardless of its specific etiology, several studies have documented that early episodes of isolated CP are associated with late adverse outcomes, such as chronic rejection (characterized by ductopenia and increased fibrosis, particularly in zone 3), a veno-occlusive–like syndrome, and de novo AIH.2, 5, 10–18 Most of the observations in these studies, however, were based on select patient groups, either groups of patients who ultimately developed CR or subsets of patients who had clinical evidence of CP or late ACR. Neither the prevalence nor natural history of isolated CP in untreated recipients has been systematically studied, primarily because of the lack of protocol liver biopsies in many institutions and the increased treatment of isolated CP over the years.

In this study, we analyzed a population of adult patients with orthotopic liver transplants (OLTs) who had routine, protocol biopsies performed posttransplant, which enabled us to determine the prevalence of isolated CP. This patient population was also unique because therapy was not given for a histologic diagnosis of isolated CP and patients with the potential to develop recurrent liver disease (viral hepatitis C and AIH, which can affect the centrilobular regions) were excluded, which allowed us to study the natural course of isolated CP.

Abbreviations

ACR, acute cellular rejection; AIH, autoimmune hepatitis; CP, central perivenulitis; CV, central vein; OLT, orthotopic liver transplant; PBC, primary biliary cirrhosis; PV, portal vein; z3, zone 3.

PATIENTS AND METHODS

The study population included 100 consecutive adult OLT patients from the Mayo Clinic (Rochester, MN) who met the following criteria: (1) OLT was performed for primary diseases that do not typically recur in zone 3 (patients with AIH were excluded from this study), (2) protocol liver biopsies were performed post-OLT, and (3) long-term (at least 3 years) posttransplant histologic and clinical follow-up was available. Patients with viral hepatitis C were also excluded from this study because of potential competing pathologies that could complicate the diagnosis of ACR (for example, it is sometimes difficult to distinguish recurrent viral hepatitis C from ACR). Patients transplanted for viral hepatitis B were included in the study if they did not develop recurrent infection. All liver biopsies, protocol and nonprotocol, from these 100 patients were reviewed. The Institutional Review Board at the Mayo Clinic approved this study.

CP was defined as centrilobular hepatocyte dropout and hemorrhage with perivenular and/or venular mononuclear inflammation. CP was graded according to the recommendations of the Banff Working Group6 (Fig. 1): minimal/indeterminate = perivenular inflammation involving a minority of central veins with patchy perivenular hepatocyte loss without confluent perivenular necrosis; mild = perivenular inflammation involving a majority of central veins with patchy perivenular hepatocyte loss without confluent perivenular necrosis; moderate = mild to moderate perivenular inflammation involving a majority of central veins with at least focal confluent perivenular hepatocyte dropout without bridging necrosis; and severe = confluent perivenular hepatocyte dropout and inflammation involving a majority of hepatic venules with central-to-central bridging necrosis. We defined isolated CP as CP occurring in the absence of portal-based ACR and ≥6 weeks following an episode of portal-based ACR. All other cases of CP (nonisolated) occurred within 4 weeks of an episode of portal-based ACR or concurrently with portal-based ACR. All allograft biopsies were reviewed for CP, and when it was present, the following features were scored: classic Banff-type (portal-based) ACR,19 zone 3 fibrosis, ductopenia, and de novo AIH.

Figure 1.

CP. (A) Mild CP with mild lymphoplasmacytic inflammation, centrilobular hepatocyte dropout, and hemorrhage. (B) Moderate CP with more pronounced dropout, hemorrhage, and inflammation. (C) Severe CP with bridging necrosis. Abbreviations: CP, central perivenulitis; CV, central vein; PV, portal vein.

RESULTS

Study Population and Biopsy Numbers

There were 67 males and 33 females. Mean age at the time of transplant was 51 years (range, 17–71 years). Reasons for transplant included primary sclerosing cholangitis (n = 25), primary biliary cirrhosis (n = 17), alcoholic and nonalcoholic fatty liver disease (n = 17), viral hepatitis B infection (n = 7), alpha-1-antitrypsin deficiency (n = 7), cryptogenic cirrhosis (n = 6), familial amyloid (n = 5), Wilson disease (n = 2), fulminant hepatic failure (n = 2), polycystic liver disease (n = 2), autoimmune cholangiopathy (n = 2), metastatic ileal carcinoid (n = 1), hyperoxalosis (n = 1), hemochromatosis (n = 1), granulomatous hepatitis (n = 1), secondary sclerosing cholangitis (n = 1), chronic venous outflow obstruction (n = 1), extrahepatic portal vein thrombus (n = 1), and cholangiocarcinoma (n = 1). A total of 572 allograft biopsies were performed, resulting in a mean of 5.7 (range, 3–11) biopsies per patient (Table 1). Most patients (88%) received tacrolimus-based immunosuppression.

Table 1. Summary of the Biopsies Taken in This Study
Total number of biopsies 572
 Mean number of biopsies per patient5.7 (range, 3–11)
  1. Abbreviations: ACR, acute cellular rejection; CP, central perivenulitis.

Timing of the biopsies (range, 4 days to 7.25 years)0 to 3 months222
3+ months to 1 year160
 1+ to 3 years87
 >3 years103
Number of biopsies with isolated CP58 (10%)
 Mean number of biopsies per patient2.1 (range, 1–6)
Number of biopsies with CP associated with portal-based ACR59 (10%)

Prevalence of CP and Isolated CP

The results of the findings are summarized in Table 1 and Fig. 2. Among 572 allograft biopsies, 59 (10%) showed CP associated with portal-based ACR, and 58 (10%) others showed isolated CP (Table 1). Forty patients had evidence of CP; of these, 88% were receiving tacrolimus-based immunosuppression (the same frequency as the entire study population). The initial diagnoses prior to transplant for the patients with CP (compared to the entire study group) were primary biliary cirrhosis (11 of 17, 65%), primary sclerosing cholangitis (9 of 25, 36%), viral hepatitis B infection (5 of 7, 71%), alcoholic and nonalcoholic fatty liver disease (4 of 17, 24%), autoimmune cholangiopathy (2 of 2), Wilson disease (2 of 2), cryptogenic cirrhosis (2 of 6, 33%), alpha-1-antitrypsin deficiency (1 of 7, 14%), fulminant hepatic failure (1 of 2), metastatic ileal carcinoid (1 of 1), hemochromatosis (1 of 1), and chronic venous outflow obstruction (1 of 1). Isolated CP was documented in 28 (28%) adult patients at some point during their posttransplant course (Fig. 2). Of these, 16 (56%) had experienced previous (>6 weeks prior) episodes of portal-based ACR, whereas 12 had no prior evidence of ACR. Isolated CP tended to occur late; biopsies showing isolated CP were taken at a mean of 658 days posttransplant (range, 7–2223 days). The mean time to the first biopsy with isolated CP was 422 days (range, 7–1825 days). Of the 28 patients with isolated CP, the average number of biopsies per patient demonstrating isolated CP was 2.1 (range, 1–6; Table 1).

Figure 2.

Natural history and outcomes of “transplant-associated” inflammation and CP. All but 1 patient with late liver injury had evidence of late inflammation. At last follow-up, all patients were alive; 2 patients had persistently elevated alkaline phosphatase levels (one with bridging fibrosis and one with de novo AIH). *“CP & portal-based ACR” reflects CP associated with portal-based ACR, either on the same biopsy or on a recent prior biopsy; these patients never had isolated CP. **“Late” inflammation in this chart is >3 months post-OLT. Abbreviations: ACR, acute cellular rejection; AIH, autoimmune hepatitis; CP, central perivenulitis; OLT, orthotopic liver transplant; PBC, primary biliary cirrhosis; z3, zone 3.

Natural History and Adverse Outcomes of Isolated CP

In our population, isolated CP was generally not treated with increased immunosuppression, but CP associated with portal-based ACR was treated. This allowed us to follow the natural course of isolated CP. We documented late episodes of allograft inflammation (CP and/or portal-based ACR) and the potential adverse outcomes of (1) development of zone 3–based fibrosis, (2) ductopenia, and (3) de novo AIH. The results are summarized in Fig. 2.

Late Allograft Inflammation

The definition of “late” is somewhat arbitrary in reference to posttransplant events and varies in the literature from >3 months to >1 year posttransplant. On the basis of this variation in the literature, we chose to look at 2 time points. When a cutoff of 3 months was used for “late inflammation,” 32 patients (32%) had episodes of late inflammation (“late inflammation” includes isolated CP, CP associated with portal-based ACR, or portal-based ACR alone; Table 2 and Fig. 2). In the vast majority (94%) of patients, the late inflammation was some form of CP, either isolated CP or CP associated with portal-based ACR. Only 2 (6.4%) patients had late episodes of portal-based ACR without CP, and each of these late episodes of ACR (at 4 and 8 months) was the only episode of rejection for these patients. A comparison of the 28 patients who had 1 or more episodes of isolated CP with the 12 patients who had portal-based ACR without CP showed that there was a significant association between isolated CP and late allograft inflammation; late inflammation was documented in 26 (93%) with isolated CP but in only 2 (17%) without CP (P < 0.001, Fisher exact test). Interestingly, episodes of late (>3 months) isolated CP were typically associated with only mildly to modestly abnormal liver function tests, with an average fold increase above normal of 2.1 for aspartate aminotransferase, 2.3 for alanine aminotransferase, 1.7 for alkaline phosphatase, and 1.4 for total bilirubin.

Table 2. Summary of Late Episodes of Inflammation
Definition of “Late”Number of Patients (%)Pattern of Late Inflammation (Number of Biopsies)
  • Abbreviations: ACR, acute cellular rejection; CP, central perivenulitis.

  • *

    Thirty of 40 (75%) patients with some form of CP and 2 of 12 (17%) patients with portal-based ACR had evidence of late inflammation only (P ≤ 0.001).

  • All cases of late inflammation detected at ≥1 year occurred in patients who had some form of CP.

>3 months32 (32%)*Isolated CP (n = 47)
  26 with isolated CPCP associated with portal-based ACR (n = 19)
  4 with CP associated with portal-based ACRPortal-based ACR (n = 2)
  2 with portal-based ACR only 
≥1 year21 (21%)Isolated CP (n = 34)
  19 with isolated CPCP associated with portal-based ACR (n = 6)
  3 with CP associated with portal-based ACRPortal-based ACR (n = 0)

When a cutoff of 1 year was used for “late inflammation,” 21 (21%) patients had episodes of late allograft inflammation; 19 (90%) of these had isolated CP (Table 2). All episodes of late inflammation at ≥1 year posttransplant occurred in patients who previously had CP, either in isolation or associated with portal-based ACR. Of 28 total patients in this study who had isolated CP at some time point, most (19, 68%) had at least 1 episode of late (≥1 year) allograft inflammation (all isolated CP). In contrast, none (0%) of the 12 patients with portal-based ACR without CP had late inflammation (P < 0.001, Fisher exact test).

Adverse Outcomes (Development of Zone 3 Fibrosis, Ductopenia, and De Novo AIH)

Overall, 13 patients developed adverse outcomes. Ten (10%) of 100 patients developed zone 3 fibrosis, and in 6 of these patients, there was central-central or central-portal bridging fibrosis (Fig. 2 and Table 3). Bridging fibrosis occurred late in the posttransplant course at a mean of 3.2 years. Of the 10 patients with zone 3 fibrosis, 5 (50%) had a prior or concurrent episode of severe CP, and 2 (20%) also developed de novo AIH. All cases of zone 3 fibrosis developed in patients who had either isolated CP (8 patients, including 4 with bridging fibrosis) or CP in association with portal-based ACR (2 patients, both with bridging fibrosis). In contrast, zone 3 fibrosis was not seen in any of the 12 patients who had portal-based ACR without CP or among the 48 patients without ACR (P < 0.0001, Fisher exact test). Examined conversely, zone 3 fibrosis developed in 29% of patients with isolated CP, 16.7% of patients with CP and portal-based ACR, and 0% of patients with portal-based ACR only (see Fig. 2 and Table 3). Follow-up biopsies showed some degree of plasticity to zone 3 fibrosis; 2 of the 6 patients with bridging fibrosis showed evidence of resolution of the fibrosis on subsequent biopsies. Three patients without bridging fibrosis developed mild zone 3 perivenular fibrosis; 1 patient had fibrosis at 5 and 6 years, 1 patient had fibrosis on multiple biopsies from 7 weeks to 5.9 years, and 1 patient had fibrosis at 4.6 years. The mild fibrosis was present on all of their final biopsies.

Table 3. Adverse Outcomes
OutcomeNumber of PatientsFollow-Up
  • NOTE: Adverse outcomes were seen only in patients who had concurrent or prior episodes of CP. The majority of these adverse outcomes (87%) occurred in patients with evidence of late (>3 months) inflammation.

  • Abbreviations: AIH, autoimmune hepatitis; CP, central perivenulitis.

  • *

    1 patient with zone 3 bridging fibrosis had isolated CP only.

  • 2 patients with de novo AIH had isolated CP only.

1. Zone 3 fibrosis10 (10%; 6 with bridging fibrosis*)Bridging fibrosis on last biopsy (n = 3)
  Mild zone 3 fibrosis on last biopsy (n = 4)
  Resolution of the fibrosis on subsequent biopsies (n = 3)
  Developed de novo AIH (n = 2)
2. Ductopenia3 (3%)Retransplanted at 3 months for chronic rejection (n = 1)
  Ductopenia on last biopsy (n = 2)
3. De novo AIH3 (3%)De novo AIH on last biopsy (n = 2)
  Zone 3 fibrosis (n = 2); bridging fibrosis (n = 1)

Three patients (3%) developed ductopenia (Fig. 2 and Table 3). They received liver transplants for primary sclerosing cholangitis, alcoholic cirrhosis, and primary biliary cirrhosis. All 3 had evidence of moderate (n = 1) or severe (n = 2) CP, and all had multiple (n = 7, 5, and 5) previous biopsies showing CP and/or portal-based ACR. In contrast, none of 60 patients without CP developed ductopenia, but this did not reach statistical significance. One patient required retransplant at 3 months for chronic rejection with persistent moderate CP, ductopenia, and focal foam cell arteriopathy.

Three patients (3%) developed de novo AIH (Fig. 2 and Table 3). They received liver transplants for alcoholic cirrhosis, venous outflow obstruction, and primary biliary cirrhosis. Serologically, all had positive antinuclear antibodies and negative antismooth muscle antibodies. All 3 had evidence of CP (1 each with mild, moderate, and severe CP), including 2 with isolated CP only; none of the patients without CP developed de novo AIH (not statistically significant). These 3 patients had 4, 3, and 3 prior biopsies with CP and/or portal-based ACR. One patient with ductopenia and 2 patients with de novo AIH also had evidence of zone 3 fibrosis.

These “adverse” outcomes of zone 3 fibrosis, ductopenia, and de novo AIH were seen only in patients who had experienced prior or concurrent episodes of CP; most occurred in patients who had CP associated with concurrent or prior portal-based ACR. Of the 12 patients with isolated CP who never experienced portal-based ACR, 3 (25%) developed adverse outcomes: 2 patients developed de novo AIH (at 2 years and 3.1 years), and 1 patient had persistent zone 3 bridging fibrosis at 6 years. The “adverse” outcomes were more common in patients that had episodes of severe CP than in patients who had episodes of mild CP (P < 0.05). None of the patients with only minimal CP had any of these outcomes. The majority (92%) of these adverse outcomes occurred in patients with evidence of late (>3 months) inflammation, including all cases of ductopenia and all cases of de novo AIH. Nine of the 13 patients were treated with increased or altered immunosuppression upon diagnosis of the adverse finding; 1 patient with ductopenia and 3 patients with increased zone 3 fibrosis did not receive therapy. From the clinical records, only 1 patient suffered a significantly adverse outcome: 1 patient with ductopenia failed to respond to increased immunosuppression and required retransplantation at 3 months for chronic rejection, as mentioned previously. All 40 patients with CP, including those with “adverse” outcomes, were alive at clinical follow-up within the past year (the mean time of the last posttransplant biopsy was 4 years, 7 months).

DISCUSSION

Some forms of hepatic injury are unique to the posttransplant setting. Entities such as ACR, preservation injury, and mechanical complications have been well characterized both clinically and histopathologically. Chronic rejection, de novo AIH, and recurrent biliary disease such as primary biliary cirrhosis have been more recently described and characterized. Isolated CP, as defined in this study, is now well recognized as a distinct histopathologic process in the allograft liver, but its underlying etiology and clinicopathologic significance are in need of further characterization.

The understanding of this form of centrilobular injury has evolved over the years, and this evolution parallels modifications in immunosuppressive regimens. Early in the history of liver transplantation, the main goal was to prolong survival by recognizing and preventing ACR. In 1969, Porter20 was the first to describe centrilobular necro-inflammation in liver allografts as a manifestation of ACR in untreated animal models and in humans who were treated with azathioprine. Cyclosporine, a calcineurin inhibitor, became available in the early 1980s and revolutionized immunosuppressive therapy. In combination with azathioprine and corticosteroids, patient survival, quality of life, and graft survival increased, whereas posttransplant complications decreased.21 Conflicting reports arose in the early 1990s as to the etiology of centrilobular injury in liver allografts; one study implicated azathioprine hepatotoxicity as a cause of centrilobular injury (termed “veno-occlusive disease” in that study),22 whereas two other studies linked centrilobular injury (necrosis/stenosis) to rejection, rather than azathioprine.23, 24 In 1989, tacrolimus (another calcineurin inhibitor) was introduced. It did not take long for tacrolimus to be implicated as a cause for centrilobular injury,25, 26 but subsequent reports refuted these findings.3, 4

In 1991, Demetris et al.27 showed in a rat model that the terminal hepatic venular region is a site of primary sensitization in rejection, in part because of its rich content of antigen presenting cells. To date, several groups have supported CP as an immune-mediated process, and many have associated CP with adverse outcomes, such as graft loss and the development of ductopenic rejection.2–4, 11, 15, 16, 20, 23, 24, 28, 29 Although the Banff criteria for acute rejection19 considers CP to be a feature of severe ACR, many studies1–6 have shown that even isolated CP can be a manifestation of ACR in the early posttransplant period (assuming that other etiologies, such as a vascular insult, have been excluded).

With the development of more successful immunosuppressive regimens, patients and grafts are surviving longer. Over the past few years, the long-term effects of prolonged survival on the liver allograft have begun to be characterized. Interestingly, in addition to being a component of ACR, CP has been found to be an important component of late allograft injury and dysfunction. Even though Porter20 first described centrilobular hepatocyte atrophy and centrilobular reticulin condensation and collapse as a repair mechanism following acute rejection, it has taken 3 decades to incorporate these findings into a classification scheme of chronic rejection.7 However, it is now generally accepted that isolated CP is also a characteristic feature of late-onset ACR and/or early chronic rejection.6–9 In our study, the average time to the first diagnosis of isolated CP was 422 days.

Although many studies2, 3, 5, 8, 10–18, 28 have reported on the significance of CP in liver allografts, the prevalence of isolated CP in adult liver allografts is still not known, and its actual impact on liver transplant recipients may be underappreciated. We were able to study the prevalence of “transplant-associated” isolated CP (CP unrelated to ACR or recurrent diseases such as AIH) in a group of adult liver transplant recipients who were followed with protocol liver biopsies over at least 3 years. In our population, isolated CP occurred on at least 1 occasion in 28% of patients and in 10% of all posttransplant biopsies; CP with associated portal-based ACR occurred in an additional 12 patients for a total of 40% of patients with some form of CP in their allografts. A comparison can be made between this adult population and a pediatric population in which the prevalence of CP was studied.3 In the pediatric population, isolated CP occurred in 16% of patients and 9% of posttransplant biopsies, whereas any form of CP was present in 38% of patients. The decreased rate of isolated CP in pediatric recipients could be related to several factors, including the treatment of isolated CP in that study, the lack of protocol biopsies, and the smaller percentage of cases of potentially recurrent disease. Interestingly, the observation that CP appeared more resistant to immunosuppressant therapy than portal-based ACR, occurred late posttransplant, and was associated with chronic allograft injury was made in both studies.

In our adult population, 52% of our patients experienced at least 1 episode of acute rejection, which is lower than the 64% reported in a large transplant center.9 Although nearly 50% of our population never developed acute rejection, most (70%) of those who did also developed CP either concurrently or subsequently, and it is this subgroup of patients, those who had evidence of CP, who tended to develop late allograft injury. When CP occurred late posttransplant, it tended to occur in isolation. Sixty-nine percent (69%) of biopsies showing late (>3 months) inflammation had isolated CP, whereas only 30% had CP associated with portal-based ACR; only 2 late biopsies showed portal-based ACR only. An unexpected finding was that 12 of 13 (92%) patients who developed adverse outcomes of zone 3 fibrosis, ductopenia, and/or de novo AIH experienced prior or concurrent episodes of late CP. Additionally, all cases of late CP occurred in patients who had early episodes of CP and/or portal-based ACR, and this supports studies that have associated CP in the first episode of portal-based ACR with adverse outcomes.2, 11, 18 On the basis of the results of our study, late isolated CP cannot always be detected by routine screening of liver function tests; thus, late protocol allograft biopsies appear to be warranted.

The results of our study identify isolated CP as a common occurrence in adult liver allografts, occurring in 28% of our population. Our results also emphasize the observation that early CP is predictive of late CP and that late CP (often present as isolated CP) is associated with long-term liver injury, including chronic rejection and de novo AIH. However, only 1 patient (1%) in our population experienced graft loss from chronic rejection, and this is similar to the rate of graft failure from acute or chronic rejection at a large transplant center;12 the remaining patients had intact graft function at the end of the study. Thus, although late CP is not a predictor of poor outcome or graft loss, it contributes to allograft injury in a significant minority (13%) of patients. Because isolated CP was not treated in our study, the effect of antirejection therapy on the long-term effects of CP cannot be assessed. However, we did observe that CP was more resistant to antirejection therapy than ACR because in 71% of treated episodes of portal-based ACR with CP, the CP component persisted in follow-up biopsies. Other studies have shown that CP (including isolated CP) has a variable response to antirejection therapy, with more resistance to typical therapy than portal-based ACR, but ultimately tends to respond to different or more intense antirejection regimens.1, 3, 4, 8, 10, 18

On the basis of the findings of this study and others, CP presenting at any time point posttransplant should be considered a form of cellular rejection. It is possible—but remains to be shown—that treating early CP may prevent the onset of late CP and that treating late CP, even if interpreted as a feature of early chronic rejection, may prevent morbidity due to late chronic rejection (ductopenia and fibrosis) and possibly even de novo AIH. An interesting observation in this and other studies is that late cellular rejection histopathologically appears different from early ACR in that the majority of cases of late cellular rejection are characterized by isolated CP; none of our cases of late (≥1 year) inflammation involved only the portal tracts, and only a minority involved both portal tracts and centrilobular areas. Given the association between CP and de novo AIH, fibrosis, and ductopenia in our study, one could hypothesize that the antigenicity of the liver allograft changes over time, altering the target of the immune-mediated response. Further study is needed to determine the immune target and to explain the mechanisms involved in the development of CP and late cellular rejection.

Ancillary