Severe Renal Allograft Rejection Resulting from Lenalidomide Therapy for Multiple Myeloma: Case Report.

Lenalidomide, a thalidomide analogue, is an immunomodulatory drug currently used as a chemotherapeutic agent in treating certain hematologic malignancies, including multiple myeloma. The antineoplastic effect of lenalidomide may be due to its ability to modulate different components of the immune system as well as its antiangiogenic, antiproliferative, and direct cytotoxic activity. Given its immunomodulatory effects, lenalidomide may potentially elicit unintended immune activity against allografts in solid organ transplant recipients. Here, we present a case of a renal transplant recipient who developed multiple myeloma after transplantation and was treated with the use of lenalidomide, which precipitated severe acute T-cell-mediated rejection. Lenalidomide was thought to be causative, and after cessation of the drug her renal function stabilized.

Polyclonal Regulatory T Cell Therapy for Control of Inflammation in Kidney Transplants.

Early subclinical inflammation in kidney transplants is associated with later graft fibrosis and dysfunction. Regulatory T cells (Tregs) can reverse established inflammation in animal models. We conducted a pilot safety and feasibility trial of autologous Treg cell therapy in three kidney transplant recipients with subclinical inflammation noted on 6-month surveillance biopsies. Tregs were purified from peripheral blood and polyclonally expanded ex vivo using medium containing deuterated glucose to label the cells. All patients received a single infusion of ~320 × 106 (319, 321, and 363.8 × 106 ) expanded Tregs. Persistence of the infused Tregs was tracked. Graft inflammation was monitored with follow-up biopsies and urinary biomarkers. Nearly 1 × 109 (0.932, 0.956, 1.565 × 109 ) Tregs were successfully manufactured for each patient. There were no infusion reactions or serious therapy-related adverse events. The infused cells demonstrated patterns of persistence and stability similar to those observed in non-immunosuppressed subjects receiving the same dose of Tregs. Isolation and expansion of Tregs is feasible in kidney transplant patients on immunosuppression. Infusion of these cells was safe and well tolerated. Future trials will test the efficacy of polyclonal and donor alloantigen-reactive Tregs for the treatment of inflammation in kidney transplants.

The effect of costimulatory and interleukin 2 receptor blockade on regulatory T cells in renal transplantation.

Regulatory T cells (Treg) are critical regulators of immune tolerance. Both IL-2 and CD28-CD80/CD86 signaling are critical for CD4(+)CD25(+)FOXP3(+) Treg survival in mice. Yet, both belatacept (a second-generation CTLA-4Ig) and basiliximab (an anti-CD25 monoclonal antibody) are among the arsenal of current immunotherapies being used in kidney transplant patients. In this study, we explored the direct effect of basiliximab and belatacept on the Tregs in peripheral blood both in the short term and long term and in kidney biopsies of patients with acute rejection. We report that the combined belatacept/basiliximab therapy has no long-term effect on circulating Tregs when compared to a calcineurin inhibitor (CNI)-treated group. Moreover, belatacept-treated patients had a significantly greater number of FOXP3(+) T cells in graft biopsies during acute rejection as compared to CNI-treated patients. Finally, it appears that the basiliximab caused a transient loss of both FOXP3(+) and FOXP3(-) CD25(+) T cells in the circulation in both treatment groups raising important questions about the use of this therapy in tolerance promoting therapeutic protocols.

Down-regulation of endothelial expression of endothelial cell protein C receptor and thrombomodulin in coronary atherosclerosis.

Coronary atherosclerosis with occlusive thrombosis is the major cause of acute myocardial infarction. Although plaque rupture is usually hypothesized to be the predisposing event in coronary thrombosis, the possibility cannot be excluded that local changes in the anticoagulant properties of the endothelium overlying the plaque contribute to this process. It is evident that thrombomodulin and the endothelial cell protein C receptor are critical players in the control of the thrombogenic process. This study examined whether thrombomodulin and the endothelial cell protein C receptor are down-regulated on endothelial cells overlying the atherosclerotic plaque in coronary arteries and thus could potentially favor local thrombus formation. Sections of archival left and right coronary arteries (n = 18 each) with severe atherosclerosis from the native heart of six patients who underwent heart transplantation were immunostained for CD31, CD34, endothelial cell protein C receptor, and thrombomodulin using a streptavidin-biotin-peroxidase method. Controls included left and right coronary arteries from autopsy cases with no atherosclerosis (n = 6), and also from cases with mild atherosclerosis (n = 5). The apparent density of all of these proteins was much higher in control than in atherosclerotic arteries. Our findings support the hypothesis that both endothelial cell protein C receptor and thrombomodulin are down-regulated in coronary arteries with atherosclerosis. These changes would be expected to result in reduced inhibition of thrombogenic and anti-inflammatory activity on the endothelium overlying atherosclerotic regions and thus could contribute to coronary thrombosis.

Dysfunction of endothelial protein C activation in severe meningococcal sepsis.

BACKGROUND: Impairment of the protein C anticoagulation pathway is critical to the thrombosis associated with sepsis and to the development of purpura fulminans in meningococcemia. We studied the expression of thrombomodulin and the endothelial protein C receptor in the dermal microvasculature of children with severe meningococcemia and purpuric or petechial lesions. METHODS: We assessed the integrity of the endothelium and the expression of thrombomodulin and the endothelial protein C receptor in biopsy specimens of purpuric lesions from 21 children with meningococcal sepsis (median age, 41 months), as compared with control skin-biopsy specimens. RESULTS: The expression of endothelial thrombomodulin and of the endothelial protein C receptor was lower in the patients with meningococcal sepsis than in the controls, both in vessels with thrombosis and in vessels without thrombosis. On electron microscopical examination, the endothelial cells were generally intact in both thrombosed and nonthrombosed vessels. Plasma thrombomodulin levels in the children with meningococcal sepsis (median, 6.4 ng per liter) were higher than those in the controls (median, 3.6 ng per liter; P=0.002). Plasma levels, protein C antigen, protein S antigen, and antithrombin antigen were lower than those in the controls. In two patients treated with unactivated protein C concentrate, activated protein C was undetectable at the time of admission, and plasma levels remained low. CONCLUSIONS: In severe meningococcal sepsis, protein C activation is impaired, a finding consistent with down-regulation of the endothelial thrombomodulin-endothelial protein C receptor pathway.

Outcome of renal transplantation in fibrillary glomerulonephritis.

Fibrillary glomerulonephritis (FGN) is a rare but progressive glomerular disease usually with end-stage renal disease (ESRD) developing within months or few years following the diagnosis. Little is known about the outcome of renal transplantation in patients with ESRD due to FGN. We report four patients with FGN who received renal allografts. Two patients developed recurrent FGN in their grafts. One patient was diagnosed to have recurrent FGN 9 years post-transplant, and lost his graft 4 years thereafter. Another patient had recurrent disease 2 years post-transplant but has stable graft function after 7 years. One patient died with normal renal allograft function 7 years following transplantation. The fourth patient has chronic transplant nephropathy 34 months post-transplant without evidence of recurrent FGN. A literature review revealed 10 additional patients who received 11 renal allografts due to ESRD caused by FGN. Four of these 10 patients had biopsy-proven recurrence (one patient in two subsequent grafts), but this caused graft loss only in 2 patients 56 months and 7 years post-transplant, respectively. The earliest recurrence was diagnosed 2 years post-transplant. We conclude that although the recurrence rate of FGN in renal transplants is high (around 50%), the recurrent disease has a relatively benign course and prolonged graft survival is possible.

Down-regulation of renal endothelial nitric oxide synthase expression in experimental glomerular thrombotic microangiopathy.

Infection with certain strains of Escherichia coli and endotoxemia results in renal glomerular thrombotic microangiopathy (TMA) characterized by endothelial swelling and prominent glomerular microthrombus formation. Nitric oxide (NO) is an endogenous biologic modulator with diverse physiologic functions including vasodilation and inhibition of platelet adhesion and aggregation. NO is synthesized from conversion of L-arginine to L-citrulline by a family of NO synthases (NOS), which include constitutive and inducible isoforms. Indirect evidence supports the hypothesis that TMA is associated with depressed intrarenal NO production. However, the effect of TMA on renal tissue NOS expression has not been fully elucidated. We studied rats with TMA induced by iv bolus injection of high dose (20 mg/kg) E. coli endotoxin. Subgroups of six animals each were sacrificed before or at 30, 90, 180, 360, and 720 minutes after the administration of endotoxin. Renal histology and tissue expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS) were examined. Additionally, we examined the effect of endotoxin on glomerular NO production, and eNOS and iNOS protein expression in vitro. Glomerular capillary thrombosis developed by 180 minutes after endotoxin administration in approximately half of the animals. The glomeruli without thrombotic lesions apparent by light microscopy disclosed early signs of TMA characterized by endothelial swelling, platelet accumulation/adhesion, and patchy fibrinogen deposition. These morphologic changes were associated with a marked reduction of renal tissue eNOS expression beyond 180 minutes after the endotoxin administration. The fall in eNOS expression was coupled with a significant rise in iNOS protein abundance, which was expressed largely by glomerular circulating neutrophils and endothelial cells, peritubular vascular endothelium, and collecting ducts of cortex and medulla. In vitro incubation of isolated glomeruli with endotoxin also resulted in a marked reduction in eNOS expression and a significant rise in iNOS content. Administration of E. coli endotoxin leads to a sustained fall in renal eNOS expression both in vivo and in vitro. The associated decline in intrarenal endothelial NO production/availability may result in renal vasoconstriction and a hypercoagulative state, which may contribute to the pathogenesis of endotoxin-induced TMA.

The endothelial cell protein C receptor aids in host defense against Escherichia coli sepsis.

The influence of the endothelial protein C receptor (EPCR) on the host response to Escherichia coli was studied. Animals were treated with 4 separate protocols for survival studies and analysis of physiologic and biochemical parameters: (1) monoclonal antibody (mAb) that blocks protein C/activated protein C binding to EPCR plus sublethal numbers of E coli (SLEC) (n = 4); (2) mAb to EPCR that does not block binding plus SLEC (n = 3); (3) SLEC alone (n = 4); and (4) blocking mAB alone (n = 1). Those animals receiving blocking mAb to EPCR plus sublethal E coli died 7 to 54 hours after challenge, whereas all animals treated with the other protocols were permanent survivors. Histopathologic studies of tissues from animals receiving blocking mAb plus SLEC removed at postmortem were compared with those animals receiving SLEC alone killed at T+24 hours. The animals receiving the blocking mAb exhibited consumption of fibrinogen, microvascular thrombosis with hemorrhage of both the adrenal and renal cortex, and an intense influx of neutrophils into the adrenal, renal, and hepatic microvasculature, whereas the tissues from animals receiving only sublethal E coli exhibited none of these abnormal histopathologic changes. Compared with the control animals, the animals receiving the blocking mAb exhibited significantly elevated serum glutamic pyruvic transaminase, anion gap, thrombin-antithrombin complex, IL-6, IL-8, and soluble thrombomodulin. The levels of circulating activated protein C varied too widely to allow a clear determination of whether the extent of protein C activation was altered in vivo by blocking protein C binding to EPCR. We conclude that protein C/activated protein C binding to EPCR contributes to the negative regulation of the coagulopathic and inflammatory response to E coli and that EPCR provides an additional critical step in the host defense against E coli. (Blood. 2000;95:1680-1686)

Association of renal injury with increased oxygen free radical activity and altered nitric oxide metabolism in chronic experimental hemosiderosis.

Chronic iron (Fe) overload is associated with a marked increase in renal tissue iron content and injury. It is estimated that 10% of the American population carry the gene for hemochromatosis and 1% actually suffer from iron overload. The mechanism of iron overload-associated renal damage has not been fully elucidated. Iron can accelerate lipid peroxidation leading to organelle membrane dysfunction and subsequent cell injury/death. Iron-catalyzed generation of reactive oxygen species (ROS) is responsible for initiating the peroxidatic reaction. We investigated the possible association of oxidative stress and its impact on nitric oxide (NO) metabolism in iron-overload-associated renal injury. Rats were randomized into Fe-loaded (given 0.5 g elemental iron/kg body weight as iron dextran; i.v.), Fe-depleted (given an iron-free diet for 20 weeks), and control groups. Renal histology, tissue expression of endothelial and inducible nitric oxide synthases (eNOS and iNOS), renal tissue expression of nitrotyrosine, plasma, and renal tissue lipid peroxidation product, malondialdehyde (MDA), and plasma and urinary NO metabolites (NOx) were examined. Iron overload was associated with mild proteinuria, tissue iron deposition together with significant glomerulosclerosis, tubular atrophy, and interstitial fibrosis. Rare focal glomerulosclerosis and tubulointerstitial changes were noted in normal controls. No renal lesions were observed in Fe-depleted rats. Iron deposits were seen in glomeruli, proximal tubules, and interstitium. The iron staining in the distal tubules was negligible. Both plasma and renal tissue MDA and renal tissue nitrotyrosine were increased significantly in Fe-loaded rats compared with control rats. In contrast, Fe-depleted animals showed a marked reduction in plasma and renal tissue MDA and nitrotyrosine together with significant elevation of urinary NOx excretion. In addition, iron-overload was associated with up-regulation of renal eNOS and iNOS expressions when compared with the control and Fe-depleted rats that showed comparable values. In conclusion, chronic iron overload resulted in iron deposition in the glomeruli and proximal tubules with various renal lesions and evidence of increased ROS activity, enhanced ROS-mediated inactivation, and sequestration of NO and compensatory up-regulation of renal eNOS and iNOS expressions. However, iron depletion was associated with reduced MDA and tissue nitrotyrosine abundance, increased urinary NOx excretion, normal nitric oxide synthase (NOS) expression, and absence of renal injury. These findings point to the possible role of ROS in chronic iron overload-induced renal injury.

Effect of L-aminocarnitine, an inhibitor of mitochondrial fatty acid oxidation, on the exocrine pancreas and liver in fasted rats.

Fasting induces pancreatic secretory lipase, possibly through an increased utilization of fatty acids and/or ketone bodies by the acinar cells. To test this hypothesis, the effects of L-aminocarnitine (ACA), an inhibitor of mitochondrial beta-oxidation and ketone body formation, on the pancreatic enzyme composition were studied in rats. The characteristics and reversibility of the hepatic steatosis produced by ACA in fasted animals were also investigated. In fasted rats, ACA decreased the plasma levels of beta-hydroxybutyrate, glucose and insulin, but increased that of glucagon. Fasting for 3 days increased the pancreatic lipase content by 80%. Administration of ACA (3, 10 or 30 mg kg(-1) daily) for 3 days to fasted rats led to dose-related decreases in pancreatic lipase content, the fasting-induced increase was prevented even by the lowest dose. Nevertheless, ACA in the fasted rats likewise decreased the pancreatic contents of protein, amylase and trypsinogen to varying degrees, suggesting a general defect of protein synthesis. The 3-day treatment with ACA during fasting led to dose-related, marked increases in hepatic weight and triglyceride content. Light and electron microscopy revealed lipid vesicles of varying sizes in the hepatocytes; the fat deposition was predominant in the periportal zones of the hepatic lobules. By means of electron microscopy, lipid vacuoles were observed in the centroacinar cells, but not in the acinar cells of the pancreas. In rats treated with 30 mg kg(-1) of ACA daily for 3 days while they were fasted, cessation of ACA treatment and refeeding with normal chow led to normalization of the pancreatic enzyme contents within 6 days, and gradual and complete disappearance of the hepatic steatosis within 24 days. Microscopy also demonstrated complete recovery in both the liver and the pancreas. The results indicate that pancreatic secretory lipase induction during the adaptive phase of starvation is dependent on an unhindered mitochondrial beta-oxidation of fatty acids and ketogenesis. The dose-related degree of hepatic triglyceride accumulation which can be produced readily by administration of ACA during short-term starvation in the rat may serve as a new, convenient experimental model for studies of fatty liver.

Divergent inducible expression of P-selectin and E-selectin in mice and primates.

We used in vitro and in vivo approaches to examine whether tumor necrosis factor-alpha (TNF-alpha) and oncostatin M (OSM), cytokines that bind to distinct classes of receptors, differentially regulate expression of P- and E-selectin in murine and primate endothelial cells. In human umbilical vein endothelial cells, TNF-alpha rapidly increased mRNA for E-selectin but not P-selectin. OSM elicited little or no change in mRNA for E-selectin, but induced a delayed and prolonged increase in P-selectin mRNA. TNF-alpha and OSM did not cooperate to further enhance P- or E-selectin mRNA. Intravenous infusion of Escherichia coli, which markedly elevates plasma lipopolysaccharide and TNF-alpha, increased mRNA for E-selectin but not P-selectin in baboons. In murine bEnd.3 endothelioma cells, TNF-alpha and OSM individually and cooperatively increased mRNA and protein for both P- and E-selectin. Intravenous injection of these cytokines also individually and cooperatively increased mRNA for P- and E-selectin in mice. We conclude that the murine P- and E-selectin genes respond to both TNF-alpha and OSM, whereas the primate P- and E-selectin genes have much more specialized responses. Such differences should be considered when extrapolating the functions of P- and E-selectin in murine models of inflammation to humans.

MDC-L, a novel metalloprotease disintegrin cysteine-rich protein family member expressed by human lymphocytes.

The metalloprotease disintegrin cysteine-rich (MDC) proteins are a recently identified family of transmembrane proteins that function in proteolytic processing of cell surface molecules and in cell adhesion. Since lymphocytes must interact with a constantly changing environment, we hypothesized that lymphocytes would express unique MDC proteins. To identify MDC proteins expressed in human lymph node, a polymerase chain reaction-based strategy combined with degenerate oligonucleotide primers was employed. We report here the identification of MDC-L (ADAM 23), a novel member of the MDC protein family. The results obtained from cDNA cloning and Northern blot analysis of mRNA isolated from various lymphoid tissues indicate that a 2.8-kilobase mRNA encoding a transmembrane form, MDC-Lm, and a 2.2-kilobase mRNA encoding a secreted form, MDC-Ls, are expressed in a tissue-specific manner. MDC-L mRNA was shown to be predominantly expressed in secondary lymphoid tissues, such as lymph node, spleen, small intestine, stomach, colon, appendix, and trachea. Furthermore, immunohistochemical staining with an anti-MDC-L antibody demonstrated that cells with typical lymphocyte morphology are responsible for expression of the MDC-L antigen in these lymphoid tissues. MDC-Lm was found to be expressed on the surface of human peripheral blood lymphocytes and transformed B- and T-lymphocyte cell lines as an 87-kDa protein. Thus, we have identified a novel lymphocyte-expressed MDC protein family member.

Dose-dependent pancreatotrophic effect of cholecystokinin-octapeptide in the rat: the influence of starvation.

Cholecystokinin (CCK) and its analogues are known to exert trophic effects on the exocrine pancreas, whereas at high doses, they produce pancreatic injury. This study was carried out to study the effect of starvation on the dose-dependent pancreatotrophic effect of CCK-8 in rats. Normal or fasted rats were treated with CCK-8 doses ranging from 0.5 to 32 and 0.5 to 8 micrograms kg-1, respectively, twice daily for 5 days. Pancreatic size, protein, DNA, secretory enzyme and trypsin inhibitor (PSTI) contents as well as histology were examined. In normal rats, CCK-8 increased the pancreatic content of protein, amylase, serine proteases and PSTI with maximum values between doses of 2 and 16 micrograms kg-1. The dose of 32 micrograms kg-1, however, yielded less trophic responses. Given to fasted rats, CCK-8 increased the weight as well as protein and secretory enzyme contents of the pancreas with maximum values between doses of 1 and 4 micrograms kg-1. The first dose supramaximum for the trophic responses was as low as 8 micrograms kg-1. Histology revealed necroinflammatory damage (acinar cell vacuolization, focal cell necrosis) in the exocrine pancreas at supramaximum doses of CCK-8 in both groups. Cell necroses and vacuolization were less but present even at doses optimum for trophism and exhibited dependence on both the dose of CCK-8 and nutrition. In either the normal or fasted animals, the periinsular acini were relatively less affected by the toxic effects of CCK-8 than the teleinsular ones. The results indicate that starvation makes the exocrine pancreas more sensitive to necroinflammatory effects of CCK-8. The relative protection seen in periinsular acini suggests a modulatory influence of islet hormones on development of CCK-induced acinar cell injury.

Cell proliferation in the developing human kidney.

In a previous study, utilizing antibodies to proliferating cell nuclear antigen (PCNA), we determined the proliferation index (PI) (percentage of PCNA-positive cells) of intrinsic renal cell populations in the normal adult and pediatric kidney. We have found that the PI in both adult and pediatric kidneys was very low (below 0.5 in all examined cell populations). In our present study, we investigated cell proliferation in the developing human kidney with an antibody to PCNA. Histologically normal kidneys were collected from 25 fetuses (spontaneous abortions and stillborns) ranging from 10 wk of gestation to term. Immature mesenchyme (blastema), immature early tubules, ampulla of ureteric bud, proximal tubules, Tamm-Horsfall protein (THP)-positive tubules, distal tubules, collecting ducts, and glomeruli were evaluated separately. The PI for each cell population was calculated. The PI of immature early tubules remains high (33-43) throughout embryonic life. The PI of blastemal cells is initially similarly high, but gradually decreases starting from the second trimester. The PI of THP-positive tubules, distal tubules, collecting ducts, and glomeruli starts out relatively high (5.9, 8.6, 6.0, and 12.4, respectively) and decreases gradually as term approaches (1.8, 1.3, 1.2, and 1.4, respectively). Interestingly, as soon as proximal tubules become differentiated (appearance of light microscopic features of proximal tubular epithelium with TP lectin positive brush border), their PI becomes very low (below 1) irrespective of the age of the kidney. This is the first quantitative study to show changes of the PI in various renal cell populations during human nephrogenesis. These changes in the PI relate to the stage of differentiation of the developing nephron segments.

Human protein C receptor is present primarily on endothelium of large blood vessels: implications for the control of the protein C pathway.

BACKGROUND: The protein C anticoagulant pathway is critical to the control of hemostasis. Thrombomodulin and a newly identified receptor for protein C/activated protein C, EPCR, are both present on endothelium. EPCR augments activation of protein C by the thrombin-thrombomodulin complex. METHODS AND RESULTS: To gain a better understanding of the relationship between thrombomodulin and EPCR, we compared the cellular specificity and tissue distributions of these two receptors by using immunohistochemistry. EPCR expression was detected almost exclusively on endothelium in human and baboon tissues. In most organs, EPCR was expressed relatively intensely on the endothelium of all arteries and veins, most arterioles, and some postcapillary venules. EPCR staining was usually negative on capillary endothelial cells. In contrast, thrombomodulin was detected at high concentrations in both large vessels and capillary endothelium. Both thrombomodulin and EPCR were expressed poorly on brain capillaries. The liver sinusoids were the only capillaries in which EPCR was expressed at moderate levels and thrombomodulin was low. EPCR and thrombomodulin were both expressed on the endothelium of vasa recta in the renal medulla, the lymph node subcapsular and medullary sinuses, and some capillaries within the adrenal gland. Even in these organs the majority of capillaries were EPCR negative or stained weakly. CONCLUSIONS: These studies suggest that EPCR may be important in enhancing protein C activation on large vessels. The presence of high levels of EPCR on arterial vessels may help explain why partial protein C deficiency is a weak risk factor for arterial thrombosis.

Tissue factor expression in mesothelial cells: induction both in vivo and in vitro.

Exudative pleural effusions are characterized by a high protein content and frequently progress to loculation and fibrosis. To test the hypothesis that tissue factor (TF) plays an integral role in this process, we investigated the expression of TF by human mesothelial cells (HMC) both in vivo and in vitro, and measured the effect of serum on HMC expression of TF in vitro. In vivo TF expression was not detected in HMC of normal pleura, but was detected in HMC of pleura overlying inflamed lung. In vitro, quiescent HMC demonstrated negligible levels of TF expression; however, upon serum stimulation there was a marked induction in both TF protein level and activity, peaking at 8-9 h. In contrast, treating quiescent HMC with plasma resulted in a further small, but significant, decrease in TF expression. This serum-induced rise in TF was also reflected in TF mRNA levels and did not require de novo protein synthesis. These results suggest that induction of HMC TF expression may be important in triggering both the intrapleural activation of prothrombin and the deposition of fibrin characteristic of inflammatory effusions.

Mast cells in acute cellular rejection of human renal allografts.

Mast cells (MCs), few in the normal kidney, are found in increased number in the renal parenchyma in diseases associated with persistent chronic inflammation. MCs are not easily identified in routinely processed archival tissue sections with histochemical stains. A more reliable method of detection was provided with the introduction of MC tryptase-specific monoclonal antibodies. To determine the possible role of MCs in renal allograft rejection, we studied 28 biopsy specimens from renal allografts that had been in place for various lengths of time (from 3 days to 40 months) in patients whose primary diagnosis was acute interstitial rejection; the specimens were associated with varying degrees of interstitial fibrosis, edema, and hemorrhage. The specimens were graded on a semiquantitative scale (from 0 to 3+) for the severity of rejection, the degree of interstitial fibrosis, interstitial edema, and interstitial hemorrhage. Eosinophils, plasma cells, and MCs were quantitatively evaluated in these biopsy specimens. MCs were detected by use of a commercially available anti-MC tryptase monoclonal antibody, which proved to be an excellent tool to detect MCs in routinely processed paraffin sections. A positive correlation was found between the number of MCs and the time since transplantation (R = 0.841, P < 0.005) and between the number of MCs and the severity of interstitial fibrosis (R = 0.489, P < 0.005), as well as with interstitial edema (R = 0.517, P < 0.005). MCs were increased in number in patients with moderate (n = 18; mean, 18.00 MCs per 10 high power fields [HPFs]) and severe (n = 5; mean, 12.20 MCs per 10 HPFs) acute rejection compared with patients with mild (n = 5; mean, 2.44 MCs per 10 HPFs) acute rejection and normal kidneys (n = 6; mean, 1.75 MCs per 10 HPFs). These results suggested that MCs might play a role in the process of acute rejection of renal allografts and in the development of interstitial fibrosis.