The initial mode of presentation was unexplained abnormal liver-function tests (elevation of alkaline phosphatase with mild thrombopenia) in more than half of the patients. The remainder presented with direct or indirect signs of portal hypertension. The median delay between the first noted liver abnormality and diagnosis of nodular regenerative hyperplasia was 17 months.
Eleven patients (85%) had esophageal varices and hypertensive gastropathy on upper endoscopy. Six of them experienced gastrointestinal hemorrhage at the time of diagnosis or during follow-up. One patient developed chronic diarrhea and severe denutrition related to portal hypertensive exsudative enteropathy. Four patients underwent liver transplantation for liver insufficiency and portal hypertension. The median delay between the diagnosis of nodular regenerative hyperplasia and liver transplantation was 37 months (range 24–47). Two patients had portal vein thrombosis at the time of the liver transplantation.
Nodular regenerative hyperplasia is secondary to obliterative portal venopathy
Access to the explant of the last transplanted patient provided a glimpse of the mechanism of HIV-associated nodular regenerative hyperplasia at both radiological and pathological levels. A CT portography of the whole liver revealed figures of obliterative portal venopathy with a diffuse occlusion of the distal intrahepatic portal branches (Fig. 1a). The pathological examination of the explant disclosed a typical aspect of obliterative portal venopathy with figures of nodular regenerative hyperplasia, sinusoidal dilatation and hepatoportal sclerosis in the liver parenchyma (Fig. 1b and c). No significant fibrosis was seen.
Prothrombotic hemostatic defect assessment
Obliterative portal venopathy is frequently associated with prothrombotic disorders. We therefore screened every patient with HIV-associated nodular regenerative hyperplasia for a prothrombotic hemostatic defect. All patients with HIV-associated nodular regenerative hyperplasia had decreased levels of protein S activity (Table 3). Accordingly, the levels of free protein S antigen were also low (data not shown). One patient had a G1691A factor V mutation and another had a G20210A factor II mutation. When compared to matched controls, the levels of protein S activity were lower in HIV-positive patients with nodular regenerative hyperplasia as compared with HIV-positive patients without nodular regenerative hyperplasia and as compared with HIV-negative patients with nodular regenerative hyperplasia (Table 3). In contrast, the levels of total protein S antigen were similar in the case of HIV-positive patients with and without nodular regenerative hyperplasia and were similar to that of healthy donors (Table 3).
Levels of C4b-binding protein
To determine whether the decrease in free protein S could be attributed to a shift toward the form bound to the C4b-binding protein, levels of C4b-binding protein in the plasma of the patients were compared to those in the plasma of controls. HIV-infected patients with and without nodular regenerative hyperplasia presented with identical levels of C4b-binding protein in plasma (P = 0.530). Unexpectedly, plasma from HIV-negative patients with nodular regenerative hyperplasia had 3.6 to 5.4-fold higher levels of plasma C4b-binding protein (Table 3), possibly explaining the significant increase in total protein S in these patients.
Antiprotein S IgG
We investigated whether the reduced protein S levels in HIV-infected patients are due to an acquired antiprotein S humoral immune response. Interestingly, protein S-specific IgG was detected in the plasma of healthy donors. HIV-infected patients without nodular regenerative hyperplasia showed antiprotein S IgG levels similar to those of healthy individuals. In contrast, both HIV-negative and HIV-positive patients with nodular regenerative hyperplasia had higher levels of antiprotein S IgG than those of healthy donors and than those of patients with HIV infection without nodular regenerative hyperplasia (Fig. 2a). In the case of HIV-positive patients with nodular regenerative hyperplasia, the elevated protein S recognition by plasma IgG was associated with higher amounts of circulating IgG as compared with HIV-positive patients without nodular regenerative hyperplasia and to healthy blood donors (Table 3). Of note, the three HIV-negative patients with nodular regenerative hyperplasia who had the highest levels of antiprotein S IgG had lupus as an underlying disease.
Inhibitory activity of purified IgG toward protein S
We then investigated whether the antiprotein S IgG in patients with nodular regenerative hyperplasia can neutralize protein S function. Basal inhibition of protein S activity by IgG from healthy donors and HIV-infected patients without nodular regenerative hyperplasia was observed, probably owing to the limitations of our inhibitory assay. The inhibition of protein S activity was dependent on the concentration of IgG. IgG from HIV-positive patients with nodular regenerative hyperplasia showed consistently and significantly higher inhibitory activity toward protein S than IgG from healthy donors and IgG from HIV-positive patients without nodular regenerative hyperplasia. IgG from HIV-negative patients with nodular regenerative hyperplasia were heterogeneous in terms of protein S inhibition and did not differ significantly from that of healthy donors and HIV-infected patients without nodular regenerative hyperplasia (P = 0.329 and 0.126, respectively) (Table 3).
We present here a case series of 13 patients with nodular regenerative hyperplasia in which the only identified causal factor is HIV infection. The mode of presentation was very stereotypical: long-lasting HIV infection, exposition to antiretroviral drugs, especially didanosine, adequate immune restoration and unexplained abnormal liver-function tests or portal hypertension. Complications related to portal hypertension occurred in about half of them, and four required liver transplantation. The mechanism of HIV-associated nodular regenerative hyperplasia is unknown to date but does not seem to be related to HIV infection and acquired immunodepression per se as the majority of patients were adequately immune restored.
The CT portography of the explant of the last transplanted patient shows that the primary lesion in HIV-associated nodular regenerative hyperplasia is diffuse obliterative portal venopathy. The obliteration of the small portal veins results in ischemia of the supplied acini and regenerative hyperplasia of the remainders in order to maintain liver cell mass. This observation is in line with seminal autopsic studies on nodular regenerative hyperplasia suggesting that the primary lesion in nodular regenerative hyperplasia is obliterative portal venopathy [12–14]. We propose the term of HIV-associated obliterative portopathy (HIV-OP) to describe the present syndrome in HIV-infected patients.
Nodular regenerative hyperplasia and obliterative portal venopathy have been reported to occur not only in association with other systemic diseases, including rheumatic, vascular and myeloproliferative disorders, but also with certain drugs and congenital or acquired prothrombotic states, including acquired protein S deficiency [15,16].
Protein S serves as a cofactor for the anticoagulant reaction catalyzed by activated protein C . The prevalence of congenital protein S deficiency in the general population is estimated to be one in 29 000 . In congenital protein S deficiency, the probability of developing thrombosis by age 27 is 50% and increases to 70% by age 35 . In HIV-infected patients, protein S deficiency is reported in about 20% of patients after 15 years of HIV infection . Whether acquired reduction in protein S levels predisposes HIV-infected individuals to thrombosis is currently not clear, but it is suggested by several case reports and series [21–23].
In view of these findings, we evaluated the protein S status in our patients and found that all of them had protein S activity below physiological levels. Protein S activity was significantly lower in patients with HIV-OP as compared with matched HIV-positive controls without nodular regenerative hyperplasia and in HIV-negative patients with nodular regenerative hyperplasia of another origin. Our data thus suggest a link between protein S deficiency and the development of HIV-OP.
Interestingly, despite a marked decrease in protein S activity, the levels of total protein S in patients with HIV-OP were identical to that of HIV-positive patients without nodular regenerative hyperplasia and healthy donors, suggesting functional inactivation of circulating protein S. We indeed document increased levels of antiprotein S IgG in the plasma from patients with HIV-OP as compared with patients from the other groups, including healthy donors. Antiprotein S IgG was able to inhibit the cofactor activity of protein S toward activated protein C in a functional assay. Importantly, levels of C4b-binding protein were not altered in patients with HIV-OP. Although levels of protein S activity may be affected by multiple disease process, including liver disease and thrombosis, our data suggest that acquired antiprotein S IgG participates in the pathogenesis of HIV-OP. The presence of high levels of inhibitory antiprotein S IgG in HIV-infected patients may be explained by a persisting abnormality of B-cell activation or B-cell repertoire despite antiretroviral therapy, leading to chronic polyclonal activation . Indeed, the presence of antiprotein S antibodies was well correlated to IgG levels. The HIV-infected patients studied herein had correct CD4+ lymphocyte cell count, and half of them had dramatically increased their CD4 cell count from a very low nadir. This is known to favor the occurrence of various manifestations of the inflammatory immune restoration syndrome, including inflammatory and bona fide autoantibody-mediated autoimmune conditions [25–27].
Although the incidence of HIV-OP is unknown, it is likely to be more common than generally thought. Although we report here only patients with isolated HIV-OP, we have observed identical cases in patients coinfected with hepatitis C virus . Because patients with HIV-OP typically present clinical features resembling those of cirrhosis, liver biopsy is indicated in most cases to confirm the diagnosis. Nevertheless, in the absence of any underlying liver disease, the diagnosis of HIV-OP should be considered in the presence of unexplained abnormal liver-function tests in an HIV-infected patient, especially if decreased level of protein S is found. In this case, patients should be screened for occult portal hypertension.
Our study has the inherent limitations of any small, observational case series. Although the characteristics of the control patients were similar to those of our patients with HIV-OP, they were not selected by means of systematic random sampling, and, thus, selection bias is possible, albeit unlikely. In addition, though our data show an intriguing association between levels of antiprotein S IgG, protein S deficiency and HIV-OP, they do not prove a causal relationship. Antiprotein S IgG may be an epiphenomenon or a secondary response in patients with nodular regenerative hyperplasia, rather than the root cause. However, the absence of protein S deficiency in HIV-negative patients with nodular regenerative hyperplasia suggests that the mechanism(s) of nodular regenerative hyperplasia in these patients is (or are) different: endothelitis related to infection or to immunosuppressive drugs and inducing hepatic peliosis and nodular regenerative hyperplasia probably accounted for the majority of them. Nevertheless, we observed antiprotein S IgG activity in two of these control patients. Both of them had lower levels of protein S (71 and 74%) than the other controls and were known to have autoantibodies.
In conclusion, HIV-OP appears as a complication of treated HIV infection under HAART secondary to acquired autoimmune protein S deficiency. Although our data suggest a persistent or emerging alteration of the autoantibody repertoire despite immune restoration, a more complete understanding of this immune deregulation warrants further research. As our data implicate a prothrombotic state, use of anticoagulants is an important question to be addressed, as oral anticoagulants are effective in preventing thrombosis in congenital protein S deficiencies.
We thank Dr Mircea Chirica for his help with the explant. We thank Pr. Valérie Vilgrain and Pr. Phlippe Sogni for helpful discussions on this study.
Data are available from Dr Mallet (firstname.lastname@example.org). The dataset is not available without establishing written agreements with the authors. V.O.M., S.L.-D., J.-P.V., S.P. contributed to conception and design. V.O.M., A.V., D.L., J.-P.V., H.G., D.B., S.L.-D., S.P. contributed to analysis and interpretation of the data. Drafting of the article was done by V.O.M., S.L.-D., S.P. Critical revision of the article for important intellectual content was done by V.O.M., S.L.-D., S.P. Final approval of the article was done by V.O.M., A.V., D.L., J.P.V., H.G., D.B., S.L.-D., S.P. Provision of study materials or patients was supplied by V.O.M., A.V., D.L., J.P.V., H.G., D.B., S.L.-D., S.P.
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Keywords:© 2009 Lippincott Williams & Wilkins, Inc.
autoimmunity; HIV infections/complications; hypertension/portal/etiology; protein S deficiency