Amino-terminal conserved region in proteinase inhibitor domain of calpastatin potentiates its calpain inhibitory activity by interacting with calmodulin-like domain of the proteinase

Calpastatin is a widely distributed endogenous inhibitor protein specifically acting on calpain (Ca(2+)-dependent proteinase) and is known to interact with the calmodulin-like domain (CaMLD) of the proteinase in a Ca(2+)-dependent fashion. The calpastatin molecule consists of four inhibitory domains (domains 1-4) with mutually homologous sequences in three regions designated as A, B, and C. Acidic amphiphilic alpha-helical motifs are found in both regions A and C. We investigated the correlation between the calpain inhibition potency and the ability of calpastatin to bind to recombinant CaMLD of the mu-calpain large subunit using various mutant proteins of pig calpastatin domain 1 expressed in Escherichia coli. Substitution of conserved Leu-161 with Pro in region A caused a reduction in activity of both calpain inhibition and CaMLD binding. Additional substitution of Leu-236 with Pro in region C further decreased the calpain inhibitory activity and caused a loss of CaMLD binding ability. The effects of mutation in region C alone on the above activities were smaller than those in region A. Although a mutant of deletion in the entire region B had no calpain inhibitory activity, it retained the CaMLD binding ability. On the other hand, although a region B oligopeptide had a moderate inhibitory activity, it had no CaMLD binding ability. These results suggest that region A has a role in potentiating the inhibitory activity of calpastatin by interacting with CaMLD of calpain to form a tighter complex where region B exerts the inhibitory function.

Histamine as an activator of cell growth and extracellular matrix reconstruction for human vascular smooth muscle cells

Atherosclerosis is characterised by unusual growth of vascular smooth muscle cells (VSMCs) in the intima. We examined the effects of histamine on human VSMCs and the VSMC-derived cell line, ISS10. Histamine enhanced phosphoinositide hydrolysis, increased cytoplasmic Ca2+ level and stimulated the transcription of c-fos protooncogene, which resulted in DNA synthesis and the enhancement of proMMP-1 expression. These results indicate that histamine may play some roles in the pathological process of atherosclerosis and raise the possibility that mast cells migrating into the atherosclerotic foci are involved in the process of atherosclerogenesis.

Real-time-analysis of the calcium-dependent interaction between calmodulin and a synthetic oligopeptide of calcineurin by a surface plasmon resonance biosensor

The calcium-dependent interaction between calmodulin (CaM) and the synthetic oligopeptide of a predicted CaM-binding region of human calcineurin A-2 was analysed with an automated surface plasmon resonance biosensor, BIAcore. The oligopeptide was immobilized to a biosensor chip via the amino-terminal cysteine residue by a thiol-disulphide exchange method. The biosensor chip was regenerated by an EGTA-containing buffer after each analysis. Kinetics experiments showed that CaM bound with a high affinity to the oligopeptide in a Ca(2+)-dependent manner. The estimated rate constants of association (kass) and dissociation (kdiss) were 2.3 x 10(5) M-1.s-1 and 3.9 x 10(-3)s-1, respectively. The ratio of kdiss/kass, 1.7 x 10(-8) M, was in good agreement with the dissociation constant (Kd) of 2.4 x 10(-8) M determined from the equilibrium phase.

Transcriptional regulation of basic fibroblast growth factor gene by p53 in human glioblastoma and hepatocellular carcinoma cells

Mutations of the p53 gene are found in various human cancers. The frequency of its mutation is reported to increase during tumor progression in most tumors. In human gliomas, mutations of the p53 gene are found in about one-third of the malignant forms and in few of the benign ones, indicating their possible involvement in tumor progression. On the other hand, we have recently shown that basic fibroblast growth factor (basic FGF) plays a crucial role in tumor progression as an autocrine growth factor in tissues of human gliomas. Therefore, we hypothesized that p53 might regulate the promoter activity of the basic FGF gene, which has several GC boxes and no typical TATA box. In this study, cotransfection assays using human glioblastoma and hepatocellular carcinoma cells and establishment of stable cell lines expressing mutant-type p53 were performed. The basic FGF gene promoter was demonstrated to be regulated by p53 at the transcriptional level and its basal core promoter was found to be responsive to p53. Expression of endogenous basic FGF was also demonstrated to be activated by mutant type p53. Wild-type p53 repressed gene expression of the basic FGF and its mutant activated it in vitro, implying one of the possible pathways in tumor progression.

Analysis of calcium-dependent interaction between amino-terminal conserved region of calpastatin functional domain and calmodulin-like domain of mu-calpain large subunit

Calpain requires Ca2+ both for proteolysis of its substrates and for interaction with its endogenous inhibitor, calpastatin. Although calmodulin-like domains (CaMLDs) of large and small subunits of calpain have been suggested to be the sites for Ca(2+)-dependent interaction with calpastatin, specificity and molecular basis of the interaction have remained unclear. We investigated the interaction between the CaMLD of human mu-calpain large subunit expressed in Escherichia coli and a 19-residue synthetic oligopeptide corresponding to the region A (the amino-terminal conserved acidic region) of one of the four repetitive functional domains of calpastatin. The recombinant CaMLD bound to the oligopeptide immobilized on Sepharose beads in a Ca(2+)-dependent manner. The CaMLD failed in binding to a mutant oligopeptide with one amino acid substitution. Enhancement of fluorescence intensity of a hydrophobic probe, 2-(p-toluidino)naphthalene-6-sulfonate, was observed upon incubating with the CaMLD and further increased by Ca2+. The Ca(2+)-dependent enhancement of fluorescence intensity was strongly suppressed by the wild type oligopeptide, but not by the mutant one. Kinetic experiments were performed with BIAcore where binding of the CaMLD to the oligopeptide immobilized on a biosensor chip was detected as real time signals of surface plasmon resonance. The determined dissociation constant (KD) was 3.1 x 10(-9) M. These results suggest that the region A of calpastatin binds to the CaMLD in a specific manner similar to interactions between calmodulin-binding peptides and calmodulin where hydrophobic properties are known to be important.

Immunohistochemical reactions for fibroblast growth factor receptor in arteries of patients with moyamoya disease

The cause of moyamoya disease remains unknown, and pathophysiological mechanisms remain uncertain. Basic fibroblast growth factor (FGF) is a pluripotent polypeptide that has been shown to play roles in angiogenesis, tumorigenesis and many other processes. In a previous study, we demonstrated immunohistochemically that the amount of basic FGF was increased above normal in the superficial temporal artery (STA) of patients with moyamoya disease. To clarify the function of basic FGF in moyamoya disease, we have performed an immunohistochemical study of the STA using a polyclonal antihuman FGF receptor antibody and also have tested immunohistochemical reactions for basic FGF. Twelve surgical specimens of the STA from patients with moyamoya disease were studied. Twelve specimens of the STA from skin flaps of patients with other neurological diseases were also investigated for comparison. The sections of the STA from patients with moyamoya disease showed dense and strong FGF receptor and basic FGF immunoreactivity in endothelial cells, in cells scattered in the thickened intima, and in smooth muscle cells in the media. In contrast, the sections of the STA of control patients showed faint basic FGF immunoreactivity. The statistical analysis revealed a significant difference of basic FGF immunoreactivity between moyamoya disease and other neurological diseases (chi 2 = 23; P = 0.0001). Moderately intense FGF receptor immunoreactivity was observed in most control patients. However, the statistical analysis revealed a significant difference of FGF receptor immunoreactivity between moyamoya disease and other neurological diseases (chi 2 = 13.382; P = 0.0012).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification and characterization of membrane cofactor protein (CD46) in the human kidneys

Membrane cofactor protein (MCP, CD46) is an integral protein that serves as a cofactor for factor I in inactivating C3b/C4b deposited on the same cell membrane as C3bi/C4c+C4d. This C3b/C4b inactivation is closely associated with self-protection of host cells from autologous complement attack. We have studied the distribution and properties of MCP in the normal human kidney by immunohistochemical and immunoblotting methods using monoclonal antibodies against MCP. MCP was predominantly expressed on the juxtaglomerular apparatus. Glomerular capillary walls, mesangial areas, and tubulus were also MCP positive. Glomerulus MCP was composed of two major bands of 45-65 kDa, which were similar to those of lymphocyte MCP. The proportion of the high and low molecular weight components in glomerulus MCP, however, was considerably different from that of lymphocyte MCP among the individual samples tested. Glomerular epithelial cells and mesangial cells from an individual having equal amounts of high and low molecular weight components in the lymphocytes were cultured separately and the properties of their MCP investigated. MCP in the mesangial cells and glomerular epithelial cells showed profiles in which the upper band was predominant. The results may explain the unique distribution of the high and low molecular weight forms in the glomerulus. These forms of MCP together with factor I were all capable of inactivating C3b to C3bi. Message analysis suggested that glomerular epithelial cells and mesangial cells synthesized a single species of mRNA of 4.2 kb from which the polymorphic MCP species were generated. Flow cytometric analysis suggested that MCP was minimal in mesangial cells. These results, taken together with the previous reports on the distribution of other complement regulatory proteins, infer that the distribution profile of MCP is rather similar to that of DAF but differs from those of CD59 and CR1 in the normal human kidney; this may reflect the differences between their roles or functional properties in renal tissue.

The human T-cell leukemia virus type I Tax protein induces apoptosis which is blocked by the Bcl-2 protein

The Tax protein of human T-cell leukemia virus type I activates transcription of cellular and viral genes and can immortalize primary T lymphocytes. We have previously reported that the Tax protein transforms Rat-1 cells. Here we show that Tax-transformed Rat-1 cells detach from plates to undergo apoptotic cell death by serum deprivation. These cells exhibit DNA fragmentation into oligonucleosomal fragments and chromatin condensation. Constitutive expression of a proto-oncogene, bcl-2, effectively blocks Tax-mediated apoptosis caused by serum deprivation without affecting the levels of Tax expression and the transformed phenotype of the cells.

Immunohistochemical study for basic fibroblast growth factor and fibroblast growth factor receptor I in pituitary adenomas

Immunohistochemistry and RT-PCR of basic fibroblast growth factor (bFGF) and one of its receptors (FGFR-I) were performed in pituitary adenomas. Sixty percent of pituitary adenomas showed strong or moderate immunoreactivity to bFGF. The immunoreactivity for FGFR-I in tumor tissues showed positive correlation to that for bFGF (X2 = 6.176, P = 0.0456). Basic FGF-positive cells consisted of pituitary adenoma cells as well as folliculostellate cells and, their distribution was heterogeneous. Expressions of bFGF and FGFR-I were not related to cell proliferation of pituitary adenomas or hormones produced, suggesting that bFGF plays some role other than progression of pituitary adenomas.

Distribution of C3-step regulatory proteins of the complement system, CD35 (CR1), CD46 (MCP), and CD55 (DAF), in hematological malignancies

The distribution and levels of three membrane proteins, CD35, CD46, and CD55, which serve as complement regulators, were examined in normal peripheral blood and hematologically malignant cells. CD35 was negative in most leukemia cells regardless of the type of leukemia, although granulocytes, monocytes, and some populations of lymphocytes were CD35+. CD46 was present in all blood cells except erythrocytes, and levels were 2-8 times higher in most leukemia cells than in their mature counterparts, particularly in CML and CLL cells, except for those of B cell lineage. CD55, a widely-distributed phosphatidyl inositol-anchored protein, was more frequently lost in NHL cells than in other types of hematological malignancies. In this review, we discuss the roles, mechanisms, and clinical applications of cell-associated complement regulatory proteins in hematological malignancies.

Expression of fibroblast growth factor receptor-1 in human glioma and meningioma tissues

We examined the expression of fibroblast growth factor receptor-1 (FGFR-1), namely FLG, in tissues of 18 human gliomas, 10 human meningiomas, 3 human metastatic brain tumors, and 2 normal human brains by means of immunohistochemistry. All tissues were positively stained for FGFR-1. Primary brain tumors were more abundantly immunoreactive than normal brain tissues (Mann-Whitney U test, P < 0.05). There was significant correlation between the expression level of basic fibroblast growth factor (basic FGF) and that of FGFR-1 in tissues of human glioma (Spearman's test, P < 0.05). The expression level of FGFR-1 of tumor cells increased in correlation with that of endothelial cells in glioma tissues (Spearman's test, P < 0.001). We previously reported that basic FGF is produced in more than 90% of human glioma and meningioma tissues. Together with these data, it is suggested that basic FGF is involved in autonomous cell growth and tumorigenesis of gliomas and meningiomas as an autocrine growth factor in vivo.

The origin of human immunodeficiency virus type-1 rev gene. An evolutionary hypothesis

The Rev protein of human immunodeficiency virus type-1 is an RNA-binding posttranscriptional transregulator encoded by an accessory gene that is distinct from retroviral oncogenes and whose origin is unclear. We hypothesize that the rev gene was generated by duplication of a viral RNA segment having a secondary-structure that evolved into the Rev-responsive element (RRE). This hypothesis is based on the following findings. First, accumulated data on functional mapping of Rev, Tat, and the transmembrane protein of Env suggested that the major coding exon of rev should have been inserted into the transmembrane region of env during the course of its evolution. Experiments with equine infectious anemia virus, another complex retrovirus, also indicate that a large portion of rev is located within the dispensable transmembrane region of env. Second, base usage analysis suggests the same origin for rev and RRE. Our hypothesis may provide a new insight into the evolutionary aspect of RNA-binding transactivators.

Generation and characterization of a human immunodeficiency virus type 1 (HIV-1) mutant resistant to an HIV-1 protease inhibitor

A synthetic peptide, RPI 312, that specifically inhibits the protease of the human immunodeficiency virus type 1 (HIV-1) showed a potent inhibition on virus production, maturation, and infectivity. Treatment with this agent prevented the cleavage of Gag protein at the site between p17 and p24 in HIV-1 chronically infected MOLT-4 cells as well as in the released virus. Passage of HIV-1 in the presence of gradually increasing concentrations of this protease inhibitor resulted in emergence of a variant that could evade the drug effects. In the resistant variant the maturation of Gag proteins appeared normal, but its infectivity was reduced compared with that of the parent virus. The nucleotides coding the amino acids at and around the cleavage site between Gag proteins p17 and p24 were not changed. One point mutation (A-->G) at site 2082 of the pol gene that resulted in one amino acid change at site 84 of the protease from isoleucine to valine (I-84-->V) could be detected in the resistant variant. An HIV-1 infectious DNA clone with the I-84-->V mutation also showed reduced sensitivity to this protease inhibitor. The findings that the resistant variant had lower infectivity and was still affected by higher doses of the drug support the speculation that resistance to protease inhibitors may not be as problematic as other drug resistance.

Novel internal promoter/enhancer of HTLV-I for Tax expression

The transcription initiation signals in retroviruses lie within the long terminal repeat (LTR) sequences. We have found a new transcriptional promoter in a central portion of the genome of human T-cell leukaemia virus type I (HTLV-I). The transcription start site is located just upstream to the ATG codon of the transcriptional trans-activator molecule, tax protein (Tax). The internal promoter may provide a new insight into gene expression of HTLV-I. The mechanism of leukaemogenesis by the defective HTLV-I is also discussed. Furthermore, we have identified two repeats of a novel enhancer sequence AGTTCT, which are located around the initiation site. We call the sequence HIRE (HTLV-I Internal Regulatory Element).

Implication of membrane factors other than DAF and CD59 in complement-mediated lysis of paroxysmal nocturnal hemoglobinuria erythrocytes

Erythrocytes from two patients (F.K. and A.M.) with paroxysmal nocturnal hemoglobinuria, which were almost completely deficient in decay-accelerating factor and CD59, were found to differ in their susceptibility to homologous complement. Whereas 50-70% of F.K. erythrocytes were lysed, almost 100% of the erythrocytes from A.M. were lysed. These observations were seen under both acidified and nonacidified conditions, and regardless of whether or not the normal human serum was adsorbed with normal erythrocytes to remove natural antibodies. Erythrocytes from two other patients, J.S. and Y.K., about 85% of which did not express CD59, showed lytic profiles similar to those of patient F.K. The differences between patients were not related to levels of natural antibody or other membrane regulatory proteins such as complement receptor type I or membrane cofactor protein. Erythrocytes from F.K. and A.M. differed in their reconstitution with decay accelerating factor and CD59. While erythrocytes from F.K. were reconstituted with CD59 in a unimodal pattern, erythrocytes from A.M. showed a bimodal pattern of reconstitution assessed by flow cytometry. After reconstitution with CD59, erythrocytes from F.K. and A.M. differed in their protection against homologous complement. It is concluded that erythrocyte membrane constituents other than the known inhibitors differ in these patients.

Long cellular repeats flanking a defective HTLV-I provirus: implication for site-targeted integration

Retroviruses generally integrate as proviruses which are flanked by long-terminal repeats (LTRs) on both 5' and 3' ends. Since these LTRs are required for the efficient integration mediated by the viral integrase, it is believed that defective proviruses with a single LTR are normally formed by deletion after integration. However, we found no deletion of cellular sequences around the integration site of such a defective HTLV-1. Rather, we identified 99 bp-long direct repeats adjacent to both ends of the defective provirus. The repeated cellular sequences contained a potential poly(A) signal followed by a retroviral primer-binding-site-like sequence. The presence of the direct repeats of cellular sequences can be explained by the integration of the defective virus through homologous recombination between cellular and viral read-through sequences.

Acute promyelocytic leukemia with CD59 deficiency

CD59 is a phosphatidyl inositol-anchored protein (which is lost in paroxysmal nocturnal hemoglobinuria (PNH) cells) with the capacity to block the formation of membrane attack complex, and protects host cells from autologous complement-mediated cytolysis. We found a patient with acute promyelocytic leukemia (APL) accompanied by disseminated intravascular coagulation (DIC), the cells of which were CD59-negative. Although the CD59 deficiency in the malignant cells was not related to PNH, we offered the possibility that DIC was induced by APL lysis secondary to the deficiency of CD59.

Late cyclosporine treatment ameliorates established coronary graft disease in rat allografts

The development of post-transplantation coronary graft disease (CGD) is a major cause of late morbidity and mortality. Recent reports have suggested that CGD is a type of chronic vascular rejection, possibly enhanced by cofactors such as concurrent CMV infection and hyperlipidemia. It remains controversial whether established CGD can be improved by modifications in immunosuppressive therapy. The purpose of this study was to examine whether CsA could reverse or halt the progression of CGD after it was already established. Lewis to Fisher (F-344) heterotopic heart allografts develop CGD resembling human disease. Group 1 (n = 29) had no CsA therapy for chronic rat CMV (RCMV) infection in recipients for 8 weeks before transplant. Group 2 (n = 17) had chronic RCMV infection along with CsA therapy from days 15 to 28 post-transplant. Allografts were killed at 2 and 4 weeks and 90 days post-transplantation. In group 1, leukocyte adhesion to arterial endothelium and intimal hyperplasia were well established at 2 weeks and progressed to stenotic, proliferative arterial lesions at 4 weeks. In group 2, CsA therapy was effective in significantly reversing histologic parameters of vascular rejection such as leukocyte adhesion, intimal proliferation, and periarterial edema at 4 weeks. By 90 days, however, arterial pathology was as severe as in group 1. In conclusion, these results support the hypothesis that CGD is a form of chronic vascular rejection, and once established, can be significantly modified by CsA therapy. These effects are not permanent, and progressive CGD recurs after CsA therapy is discontinued.

A monoclonal antibody against human decay-accelerating factor (DAF, CD55), D17, which lacks reactivity with semen-DAF

Human decay-accelerating factor (DAF, CD55) is a phosphatidyl inositol-anchored glycoprotein consisting, from the N-terminus, of 4 short consensus repeats (SCR), a Ser/Thr (ST)-rich region providing O-glycosylation sites, and the membrane-anchoring unit. A mAb, named D17, was raised against purified erythrocyte-DAF. This mAb recognized DAF on blood cells and most cell lines as determined by flow cytometry and immunoblotting. Its reactivity was similar to but weaker than that of two other well-characterized mAbs to DAF, IA10 (seeing an epitope within SCR1) and 1C6 (seeing an epitope within SCR3). The reactivity of D17 with erythrocyte DAF became increased by treatment with sialidase/O-glycanase, suggesting that its epitope is located close to the O-glycosylation sites, probably within the ST-rich region or SCR4. D17 barely blocked the decay-accelerating activity of DAF. Using the three mAbs, tissue-associated and soluble forms of DAF were identified by SDS-PAGE/immunoblotting and immunohistochemical staining. IA10 and 1C6 recognized a 50 kDa protein in spermatozoa lysate and two proteins of Mr 70 and 55 kDa, respectively, in seminal fluid. These represented membrane-associated and soluble forms of DAF, which were neither recognized by mAb against membrane cofactor protein (MCP, CD46) and C3b/C4b receptor (CR1, CD35) nor by non-immune IgG. In contrast to IA10 and 1C6, D17 did not recognize either spermatozoa-DAF or seminal plasma-DAF, or the deglycosylated or untreated forms of them. Immunohistochemical analysis showed that testis was stained with IA10 but not with D17.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleolar targeting signal of Rex protein of human T-cell leukemia virus type I specifically binds to nucleolar shuttle protein B-23

Rex protein, the post-transcriptional regulator of human T-cell leukemia virus type I, is located predominantly in the cell nucleolus and is associated with the cytoplasmic accumulation of unspliced and singly spliced viral mRNAs. The N-terminal 19-amino acid segment of Rex has been identified as the nucleolar targeting signal (NOS) and shown to be important for Rex function. To study the molecular interaction between the NOS region of Rex and its binding host protein(s) in the nucleolus, we chemically synthesized a functional NOS peptide (wild type) and mutant NOS peptides. Fluorescein isothiocyanate-conjugated functional NOS peptide was rapidly taken up by human cells and was transported to the nucleolus. Using affinity chromatography, we identified nucleolar protein B-23 as the major protein that binds to NOS. We also identified two highly acidic regions of B-23 (amino acids 120-132 and 161-188) as acceptor regions for NOS. Previous experiments have suggested that B-23 functions as a shuttle protein for the nucleolar transport of ribosomal components. Our results suggest that B-23 may also serve as a shuttle for the import of Rex from the cytoplasm to the nucleolus coupled to the export of viral mRNAs containing the Rex-responsive element.

Overgrowth of human synovial cells driven by the human T cell leukemia virus type I tax gene

One of the salient pathological features of rheumatoid arthritis is synovial cell proliferation with bone erosion. Despite extensive investigation, the factors essential for synovial cell proliferation remain to be identified. Recent studies suggest that human T cell leukemia virus type I (HTLV-I) may play an important role in synovial overgrowth observed in patients with one type of chronic inflammatory synovitis. In order to confirm and extend these observations, we have established synovial cell clones (SCCs) from three HTLV-I carriers who demonstrated synovial overgrowth but were otherwise asymptomatic. HTLV-I proviral DNA randomly integrated into the cellular genome was present in 20-30% of SCCs. The SCCs carrying HTLV-I proviral DNA and expressing the tax gene exhibited high levels of proliferative potential. HTLV-I was found to function as a transcriptional trans-activator in these SCCs. Moreover, transfection of the tax expression plasmid into SCCs resulted in the same phenotype of increased proliferation and cytokine expression as exhibited by HTLV-I provirus-carrying and tax-expressing SCCs. These data suggest that tax plays a critical role not only in leukemogenesis but also in synovial overgrowth in humans.

Test for ability of decay-accelerating factor (DAF, CD55) and CD59 to alleviate complement-mediated damage of xeno-erythrocytes

We investigated the susceptibility to human complement (C) of xeno-erythrocytes into which phosphatidylinositol (PI)-anchored human C regulatory protein, decay-accelerating factor (DAF) or CD59 had been incorporated. Erythrocytes of sheep (Esh), swine (Esw), dog (Edg), and guinea pig (Egp), unsensitized with human natural antibody (Ab), were used as xeno-target. C-mediated lysis of erythrocytes (E) was induced in both classical and alternative pathways in parallel with the density of the sensitized Ab, except for Egp. The efficacy of DAF/CD59-mediated protection of the xeno E from human C, however, differed among these E species. In both classical and alternative pathways, Esh or Esw, which are non-activator surfaces, were protected by the incorporated DAF or CD59, DAF being more effective than CD59. On the other hand, CD59 was more effective than DAF in both pathways in protection of Egp, which is an alternative pathway activator. To elucidate this different behaviour of DAF and CD59, C3 step inhibition by the incorporated DAF or CD59 was measured. DAF was effective in the suppression of classical pathway-mediated C3 deposition in Esh, Esw and Egp, but not in Edg, while CD59 exhibited negligible effects in this regard. Next, inhibition of the lysis by CD59 was tested by haemolytic assay. CD59 did not block the C5b-8-mediated lysis in any xeno E. It also barely blocked C5b-9-mediated lysis, except in the case of Egp, in which CD59 partly blocked C9 attack. Membrane constituents on targets other than the incorporated complement inhibitors may be a crucial factor in the induction of cytolysis and, presumably, in hyperacute rejection.