Faculty Bibliography

CONTEXT: Establishing adequate interobserver agreement is crucial not only for standardization of patient care but also to ensure validity of findings in multi-institutional trials. OBJECTIVE: To evaluate interobserver agreement in assessing chronic hepatitis C (HCV) and acute cellular rejection (ACR) among 17 hepatopathologists involved in the 'Hepatitis C 3' trial. DESIGN: The trial is a randomized multicenter (17 institutions) study involving 312 patients undergoing transplantation for HCV. Patients are randomized to 3 treatment arms. For final data analysis, all biopsy specimens are reviewed by a central pathologist (G.J.N.). Recurrence of HCV is evaluated according to the Batts and Ludwig schema. The 1997 Banff schema is used to evaluate ACR. To assess interobserver agreement, hematoxylin-eosin-stained sections from 11 liver biopsy specimens (6 HCV and 5 ACR) were sent by the central pathologist to 16 local pathologists from 13 institutions. Statistical analysis was performed on raw ACR/HCV data as well as data grouped according to clinically significant primary endpoint cutoffs. RESULTS: Statistically significant agreement was found among all participating pathologists (P < .001). On kappa analysis, the degree of agreement was rated 'moderate' for HCV grade and stage and ACR global grading (kappa = 0.30, 0.33, and 0.37, respectively). Interobserver agreement was weaker for rejection activity index scoring of ACR (kappa = 0.15). A stronger degree of agreement was found when scores were grouped based on endpoint cutoffs (kappa = 0.76 'almost perfect' for HCV and 0.62 'substantial' for ACR).CONCLUSIONS: An overall statistically significant interobserver agreement was found among 17 pathologists using the 1997 Banff schema and the Batts and Ludwig schema

We examined the response of murine oval cells, that is, the putative liver progenitor cells, to acetaminophen. Female C57BL/6J mice were injected intraperitoneally with varying doses of N-acetyl-paraaminophen (APAP) (250, 500, 750, and 1,000 mg/kg of weight) and sacrificed at 3, 6, 9, 24, and 48 hours. In preliminary studies, we showed that anticytokeratin antibodies detected A6-positive cells with a sensitivity and specificity of greater than 99%. The oval cell reaction was quantified, on immunostaining for biliary-type cytokeratins, as both number and density of oval cells per portal tract, analyzed by size of portal tract. Acetaminophen injury was followed by periportal oval cell accumulation displaying a moderate degree of morphological homogeneity. Oval cell response was biphasic, not temporally correlating with the single wave of injury seen histologically. Increases in oval cells were largely confined to the smallest portal tracts, in keeping with their primary derivation from the canals of Hering, and increased in a dose-dependent fashion. The timing of the two peaks of the oval cell reaction also changed with increasing dose, the first becoming earlier and the second later. In conclusion, our studies indicate a marked oval cell activation during the height of hepatic injury. Oval cells appear to be resistant to acetaminophen injury. The close fidelity of mechanism and histology of acetaminophen injury between mouse and human livers makes it a useful model for investigating liver regeneration and the participation of stem/progenitor cells in that process.

BACKGROUND: Lung transplant recipients are vulnerable to immunologic, infectious, ischemic, and toxic pulmonary injuries. The authors investigated whether type II pneumocytes in the lungs of cross-gender lung transplant patients show genotypic evidence to support repopulation of the lung by stem cells of bone marrow origin, and whether the degree of repopulation was related to rejection history. METHODS: Recut sections were obtained from lung biopsy specimens from seven male recipients of transplanted lungs from female donors. Sequential immunohistochemistry and fluorescence in situ hybridization was performed on each section to evaluate for Y-chromosome-containing type II pneumocytes. RESULTS: Y-chromosome-containing type II pneumocytes were found in 9 of 25 biopsy specimens from 5 of 7 gender-mismatched male lung transplant recipients, and accounted for 0% to 0.553% of type II pneumocytes. There was no evidence of polyploidy to suggest cell-cell fusion. The number of type II pneumocytes of male karyotype showed a statistically significant relationship to the cumulative number of episodes of acute cellular rejection. CONCLUSIONS: Lung transplant recipients develop low levels of pneumocyte repopulation by bone marrow-derived stem cells or their progeny. These cells contribute minimally to the type II pneumocyte proliferation that is often present in these patients as a sequela to alveolar injury.

Communication in the stem cell field requires a common understanding of terminology and that "plasticity" phenomena are model- and, perhaps, species-dependent. Plasticity has generally been applied to unexpected differentiative events; will the term cease being useful when these unexpected pathways become recognized as normative? Four pathways of cell plasticity have now been recognized: (1) facultative, intraorgan self-renewing stem cells; (2) reversion of differentiated cells to blastema-like appearances, common in amphibians, perhaps restricted to neoplasia in mammals; (3) cells of one lineage directly changing to differentiation of another lineage cued by microenvironemental signals; (4) cell-cell fusion leading to changes in differentiation of the "incoming" cell in response to cytoplasmic and perhaps nuclear cues. In all of these, "differentiation" must be understood as a reflection of gene expression that is a highly intricate system of parallel, i.e., nonlinear molecular interactions. Present controversies regarding the plasticity of adult stem cells may be explained both by differences in experimental variables and techniques as well as by differing nonscientific, political, and/or polemical needs of investigators and commentators. Some of the variables in transplantation experiments, which are likely to be important in experimental outcome, but rarely addressed in interpretation of data, are the age of the cell donor and of the strain of mice or species used, the isolation technique used to obtain the putative stem cells, and the inherent effects of transgenic markers used to identify the donor or host cells. Also of great importance, but rarely controlled for in experimental design and interpretation, are the reproducibility and sensitivity of methods used to detect the markers of donor origin, the capacity of differentiated tissue to silence transgenes or alter marker expression, and--finally and most importantly--the different signals that influence plasticity phenomena in very different types of injury and regeneration. In different models of injury there are likely to be significant differences in promoting cell localization, proliferation, and predominance of "plasticity pathway," if any are involved, in determining outcome.

The canals of Hering (CoH) begin in the lobules, are lined partially by cholangiocytes and partly by hepatocytes, and conduct bile from bile canaliculi to terminal bile ducts in portal tracts. They are not readily apparent on routine histological staining but are highlighted by the biliary cytokeratins CK19 and CK7. There is on average 1 CoH per 10 microm of bile duct length. The canals represent the true hepatocytic-biliary interface that thus lies within the lobule and not at the limiting plate. The CoH are destroyed early in primary biliary cirrhosis, perhaps explaining lobular "hepatitis" in this disease. They may also be the primary sites of scarring in methotrexate toxicity. Most intriguingly, the CoH have been speculated to harbor intraorgan stem cells of the liver, perhaps forming the hepatic stem cell "niche" and have been demonstrated to proliferate in disease states.