Effect of anticomplement agent K76 COOH on hamster-to-rat and guinea pig-to-rat heart xenotransplantation

In normal rats, the xenobiotic K76 inhibited the C5 and probably the C2 and C3 steps of complement and effectively depressed classical complement pathway activity, alternative complement pathway activity, and the C3 complement component during and well beyond the drug's 3-hr half-life. It was tested alone and with intramuscular tacrolimus (TAC) and/or intragastric cyclophosphamide (CP) in rat recipients of heterotopic hearts from guinea pig (discordant) and hamster (concordant) donors. Single prevascularization doses of 100 and 200 mg/kg increased the median survival time of guinea pig hearts from 0.17 hr in untreated controls to 1.7 hr and 10.2 hr, respectively; with repeated injections of the 200-mg dose every 9-12 hr, graft survival time was increased to 18.1 hr. Pretreatment of guinea pig heart recipients for 10 days with TAC and CP, with or without perioperative splenectomy or infusion of donor bone marrow, further increased median graft survival time to 24 hr. Among the guinea pig recipients, the majority of treated animals died with a beating heart from respiratory failure that was ascribed to anaphylatoxins. Hamster heart survival also was increased with monotherapy using 200 mg/kg b.i.d. i.v. K76 (limited by protocol to 6 days), but only from 3 to 4 days. Survival was prolonged to 7 days with the addition of K76 of intragastric CP at 5 mg/kg per day begun 1 day before operation (to a limit of 9 days); it was prolonged to 4.5 days with the addition of intramuscular TAC at 2 mg/kg per day beginning on the day of transplantation and continued indefinitely. In contrast to the limited efficacy of the single drugs, or any two drugs in combination, the three drugs together (K76, CP, and TAC) in the same dose schedules increased median graft survival time to 61 days. Antihamster antibodies rapidly increased during the first 5 days after transplantation, and plateaued at an abnormal level in animals with long graft survival times without immediate humoral rejection. However, rejection could not be reliably prevented, and was present even in most of the xenografts recovered from most of the animals dying (usually from infection) with a beating heart. Thus, although effective complement inhibition with K76 was achieved in both guinea pig- and hamster-to-rat heart transplant models, the results suggest that effective interruption of the complement cascade will have a limited role, if any, in the induction of xenograft acceptance.

Acute electrical stimulation of lateral hypothalamus increases natural killer cell activity in rats

Natural killer cell (NK) activity in WKA and SD rats was found to be significantly higher following electrical stimulation of the lateral hypothalamus (LH) compared to sham operated. There was no such difference between sham operated rats and those receiving electrical stimulation in the frontal cortex as a control. Operations were performed under sodium pentobarbital anesthetic, and NK activity against YAC-1 target cells was measured 20 h later using 51Cr release assay. The LH area stimulated is a potent reward center and that stimulation of this point increased NK activity opens the possibility that pleasure might play a role in cellular immunity.

[A case of abdominal tuberculous lymphadenitis diagnosed by percutaneous needle biopsy under ultrasound control and followed up by ultrasound imaging]

A case of abdominal tuberculous lymphadenitis diagnosed by percutaneous needle biopsy under ultrasound control and followed up by ultrasound imaging was reported. A 63 years-old male was admitted to a certain hospital complaining of dizziness and diplopia. Chest roentgenogram showed bilateral infiltrative shadows in the upper lung fields and Mycobacterium tuberculosis was detected in cultures from specimens of gastric aspiration. Abdominal ultrasound examination and computed tomography showed abdominal lymph nodes swelling. Needle biopsy under ultrasound control was performed, and the specimens showed necrosis and Mycobacterium tuberculosis was positive by culture. He was diagnosed as lung tuberculosis with abdominal tuberculous lymphadenitis and admitted to our hospital for anti-tuberculous chemotherapy. Ultrasound examination done every two weeks showed diminution in size of the lymph nodes after a month of anti-tuberculous therapy. For the diagnosis of abdominal lymph node swelling, a needle biopsy under ultrasound control is safe and useful technique, and a ultrasound examination is also valuable to follow up the course of abdominal tuberculous lymphadenitis.

[Changes in the working status of pulmonary tuberculosis patients after the admission]

We reported changes in the working status of pulmonary tuberculosis patients after the admission to our hospital. The age of patients ranged from 20 to 69 years old, and they were admitted to the 18th ward of our hospital from April 1991 to March 1993. We sent out the questionnaire to 198 patients, and the reply was sent back from 116 patients (Male 74, Female 42). Out of the 116 patients, we excluded the unemployed, the government employees, and self-employed workers. The remaining 76 patients were examined about their working status after admission, and the results were as follows: 2 patients lost their work, 11 patients retired from the work, 2 patients faced the drop of their position, and 3 patients had their salary reduced.

Seasonal changes in mite allergen (Der I and Der II) concentrations in Japanese homes

BACKGROUND

There has been no report on seasonal changes in Der II allergen in floor and bedding dust.

OBJECTIVE

The purpose of this study was to examine the extent of seasonal changes in Der I and Der II allergens in the floor and bedding dust found in houses.

METHODS

We measured the absolute concentrations of mite allergens in dust collected monthly for 1 year from both the floors and bedding of eight houses in Tokyo. Dust samples were obtained from eight families without regard to their allergy histories. The concentrations of the Der p I, Der f I, and Der II allergens were measured by fluorometric sandwich ELISA.

RESULTS

We found seasonal changes in the concentrations of these mite allergens. The highest concentrations of Der I (Der p I plus Der f I) and Der II (Der p II plus Der f II) were present from August to October, and the lowest ones from March to April. In floor dust, the mean highest concentrations of Der I and Der II (35.0 and 20.2 microgram of fine dust) were sevenfold and fivefold respectively, times the mean lowest concentrations. In bedding dust, the mean highest concentrations of Der I and Der II (51.3 and 29.6 microgram/g of fine dust) each were fourfold times the mean lowest concentrations.

CONCLUSIONS

The patterns of seasonal changes in Der II in floor and bedding dust were similar to those of Der I.

[Primary pulmonary malignant lymphoma of the T-cell type]

A 65-year-old woman was referred to our department because of an abnormal shadow on the chest roentgenogram. The chest roentgenogram showed infiltrative shadows in the right middle and lower lung fields. The chest CT scan showed non-segmental infiltration with a hazy margin and a clear air bronchogram in the right S8 area. A transbronchial aspiration cytology specimen showed atypical lymphocytes, and a transbrochial lung biopsy specimen showed infiltration by atypical lymphocytes. Malignant lymphoma was suspected from the results of the biopsy examination, and a right middle and lower lobectomy was done. The pathological findings showed proliferative atypical lymphocytes in the alveolar and interstitial areas. Malignant lymphoma (diffuse medium cell type by LSG classification) was diagnosed and an immunohistiochemical examination showed monoclonal proliferation of T lymphocytes, which were positive for T lymphocyte surface marker (UCHL-1). Therefore, we believe this was a case of primary pulmonary malignant lymphoma of the T-cell type.

Induction of anti-tumor immunity by mouse tumor cells transfected with mouse interleukin-12 gene

Interleukin-12 (IL-12) is a heterodimeric cytokine. In order to transduce both cDNAs for p35 and p40 of IL-12 in the tumor cells, a polycistronic retroviral vector was constructed by inserting the internal ribosome entry site gene of encephalomyocarditis virus between two cDNAs. On the other hand, two cDNAs were sequentially transfected in the tumor cells. Both polycistronic gene transfectants and double transfectants produced biologically active mouse IL-12. IL-12-expressing tumor cells were all rejected in syngeneic mice, and induced cytotoxic T lymphocyte activity. The capacity to induce anti-tumor memory may depend on the amount of IL-12 produced by the transfectants, because the relatively higher IL-12 producer tumor cell line induced the anti-tumor memory in the rejected mice, but the lower producer did not.

Sensitivity to two major allergens (Cry j I and Cry j II) in patients with Japanese cedar (Cryptomeria japonica) pollinosis

BACKGROUND

Japanese cedar (Cryptmeria japonica: CJ) pollinosis is one of the most important allergic diseases in Japan. Recently, the second major allergen (Cry j II) was isolated from CJ pollen. There have been no prevalence studies of sensitivity to Cry j I and Cry j II among a large number of patients with pollinosis.

OBJECTIVE

This study was conducted to evaluate the prevalence of sensitivity to Cry j I and Cry j II. We measured specific IgE antibodies to these allergens in the sera of 145 patients. Furthermore, comparison of the sensitivity to Cry j I and Cry j II was examined by the histamine release assay.

METHODS

Specific IgE antibodies to Cry j I and Cry j II were assayed by a fluorometric ELISA. Allergen-specific histamine release was measured by a radioimmunoassay kit.

RESULTS

More than 90% of 145 patients had specific IgE antibodies to both allergens, the remainder had specific IgE to either one or the other. There were seasonal changes in the level of specific IgE. The changes in the levels of anti-Cry j II IgE antibodies were parallel to those of anti-Cry j I IgE. The histamine release assay with leucocytes from the patients demonstrated that the allergenic potency of the two allergens is almost the same.

CONCLUSION

Cry j II is an as important a major allergen as Cry j I.

Temperature-sensitive mutation of DNA polymerase alpha induces growth-suppressive phenotypes involving retinoblastoma protein and cyclin D1

Temperature-sensitive (ts) cell cycle mutant mouse cell, tsFT20, is deficient in DNA polymerase alpha activity to initiate DNA replication at replicon origins. Here, we analyzed phenotypes concerning growth control genes in the arrested tsFT20 cells. Analysis of cyclins showed that expression levels of cyclin D1, which is essential for G1/S transition, remarkably decreased in the mutant cells after temperature up-shift. Further we examined phosphorylation states of retinoblastoma protein (pRB) in the cells. Though the tsFT20 cells arrested in G1/S-S phase at nonpermissive temperature (Eki et al., (1990) J. Biol. Chem. 265 26-33), a large proportion of pRB was found as an underphosphorylated growth-suppressive form in the arrested cells. In revertant cell lines of tsFT20, pRB was not underphosphorylated even at nonpermissive temperature. The pRB underphosphorylation occurred later than the decrease of mRNA levels of cyclin D1, thus the underphosphorylation may be caused by the decrease in amount of cyclin D1 protein. These results indicated that the mutational inactivation of DNA polymerase alpha evokes phenotypes in which the inhibitory machinery of G1/S transition has been turned on.

Variable chimerism, graft-versus-host disease, and tolerance after different kinds of cell and whole organ transplantation from Lewis to brown Norway rats

The bidirectional paradigm of tolerance involving reciprocal host vs. graft and graft vs. host reactions was examined after Lewis (LEW)-->Brown Norway (BN) transplantation of different whole organs (liver, intestine, heart, and kidney) or of 2.5 x 10(8) LEW leukocytes obtained from bone marrow, spleen, lymph nodes, and thymus. The experiments were performed without immunosuppression or under 14 daily doses of postoperative tacrolimus, which were continued in weekly doses to 100 days in a "continuous treatment" subgroup, and to 27 days in a short treatment group. Without immunosuppression, all organs and cell suspensions failed to engraft or were acutely rejected. GVHD (usually fatal) was always caused when either the long or short treatment was used for recipients of intestinal grafts and cell suspensions of spleen and lymph nodes. In contrast, both immunosuppressive protocols allowed engraftment of bone marrow cells, liver, heart, and kidney without clinical GVHD, whereas thymus cell suspensions and small doses of whole blood neither engrafted nor caused GVHD. At 100 days, now drug-free for 73 days, the liver, bone marrow, and heart recipients were tolerant in that they accepted all challenge LEW heart and/or liver grafts for 100 more days despite in vitro evidence of donor-specific reactivity (split tolerance). At 200 days, histopathologic studies of the challenge livers were normal no matter what the priming graft. However, the still-beating challenge hearts had a spectrum from normal to severe chronic rejection that defined the tolerogenicity of the original primary grafts: liver best-->bone marrow next-->heart least. Both the GVHD propensity and tolerogenicity in these experiments were closely associated with recipient tissue chimerism 30 and 100 days after the experiments began. The tissue chimerism was invariably multilineage, but the GVHD outcome was associated with T cell over-representation. These observations provide guidelines that should be considered in devising leukocyte augmentation protocols for human whole organ recipients. The results are discussed in relation to the historical tolerance studies of Billingham, Brent, and Medawar; Good; Monaco; and Calne.

Assignment of the 49-kDa (PRIM1) and 58-kDa (PRIM2A and PRIM2B) subunit genes of the human DNA primase to chromosome bands 1q44 and 6p11.1-p12

DNA primase is an essential replication protein that catalyzes the synthesis of oligoribonucleotide primers. DNA primase, consisting of two subunits (p49 and p58), plays a key role in both the initiation of DNA replication and the synthesis of Okazaki fragments for lagging strand synthesis. We mapped the locations of human chromosomes of the genes coding for both subunits [p49 (PRIM1) and p58 (PRIM2)] by PCR amplification using DNAs of a panel of somatic hybrids, to chromosomes 1 and 6, respectively. The PRIM1 gene was mapped to 1q44, and two PRIM2 loci (PRIM2A and PRIM2B) were detected at 6p11.1-p12 by fluorescence in situ hybridization using several genomic DNA probes.

Site-specific initiation of DNA replication in Xenopus egg extract requires nuclear structure

Previous studies have shown that Xenopus egg extract can initiate DNA replication in purified DNA molecules once the DNA is organized into a pseudonucleus. DNA replication under these conditions is independent of DNA sequence and begins at many sites distributed randomly throughout the molecules. In contrast, DNA replication in the chromosomes of cultured animal cells initiates at specific, heritable sites. Here we show that Xenopus egg extract can initiate DNA replication at specific sites in mammalian chromosomes, but only when the DNA is presented in the form of an intact nucleus. Initiation of DNA synthesis in nuclei isolated from G1-phase Chinese hamster ovary cells was distinguished from continuation of DNA synthesis at preformed replication forks in S-phase nuclei by a delay that preceded DNA synthesis, a dependence on soluble Xenopus egg factors, sensitivity to a protein kinase inhibitor, and complete labeling of nascent DNA chains. Initiation sites for DNA replication were mapped downstream of the amplified dihydrofolate reductase gene region by hybridizing newly replicated DNA to unique probes and by hybridizing Okazaki fragments to the two individual strands of unique probes. When G1-phase nuclei were prepared by methods that preserved the integrity of the nuclear membrane, Xenopus egg extract initiated replication specifically at or near the origin of bidirectional replication utilized by hamster cells (dihydrofolate reductase ori-beta). However, when nuclei were prepared by methods that altered nuclear morphology and damaged the nuclear membrane, preference for initiation at ori-beta was significantly reduced or eliminated. Furthermore, site-specific initiation was not observed with bare DNA substrates, and Xenopus eggs or egg extracts replicated prokaryotic DNA or hamster DNA that did not contain a replication origin as efficiently as hamster DNA containing ori-beta. We conclude that initiation sites for DNA replication in mammalian cells are established prior to S phase by some component of nuclear structure and that these sites can be activated by soluble factors in Xenopus eggs.

[Four cases of hemolytic uremic syndrome (HUS) associated with serotype O165 verotoxin producing Escherichia coli (VTEC) identified by LPS-solid phase enzyme-linked immunosorbent assay (ELISA)]

Enzyme-linked immunosorbent assay using LPS derived from newly recognized serotype O165 verotoxin producing Escherichia coli (VTEC) could identify 4 cases of hemolytic uremic syndrome (HUS) associated with O165 VTEC. All 4 cases showed a typical clinical course seen in VTEC-associated HUS. We screened 33 cases of HUS whose pathogen was not identified by culture of serodiagnosis. The O165 serotype was not thought to be important not only as a VTEC but also as an enteropathogenic E. coli. However, the prevalence, 4 cases, was as high as of O111 serotype, which is the second major serotype of VTEC in Japan. We have to be careful for this serotype when we look for the pathogen of the patients with hemorrhagic colitis or with HUS.

Changes in activity levels and isozyme patterns of isoleucine aminotransferase in response to experimentally induced hepatic lesion

Branched-chain amino acid aminotransferase activities were measured in rats in which hepatic lesions were induced experimentally, that is, fatty liver produced by an orotic acid-containing diet and acute hepatic lesion induced by D-galactosamine injection into the abdominal cavity. The levels of the enzyme activities, using L-isoleucine as substrate, were elevated in both cases. Among the isozymes (enzymes I, II and III) of the enzyme, the activity of enzyme I was elevated by orotic acid treatment. However, with D-galactosamine treatment, another isoleucine aminotransferase activity was chromatographically separated from that of enzyme I and is considered to be enzyme III, and not enzyme II, based on its substrate specificity.

Hamster to rat kidney xenotransplantation. Effects of FK 506, cyclophosphamide, organ perfusion, and complement inhibition

Hamster to rat renal xenotransplantation was performed with recipient nephrectomies. Recipients were treated beginning on day 0 with continuous FK 506 monotherapy, a 7-day or open-ended monotherapeutic course of cyclophosphamide (CP), and the two drug regimens combined. CP alone (10 mg/kg/day) prevented a xenospecific antibody response and tripled median survival of the kidney (defined as recipient death) from 6 (control) to 18.5 days whereas FK 506 alone had no effect. The drugs in combination were no better than CP alone (15 days) unless the 5-day course of CP was given at a higher dose (15 mg/kg) and started 3 days preoperatively (79 days). In further experiments, adjuvant measures were added to the minimally effective FK 506/7-day CP regimen which gave a median survival of only 15 days. In the most successful modification, intraoperative antibody depletion by the temporary transplantation of third party hamster liver or en bloc kidneys increased median survival from 15 to 34 and 48 days, respectively. An intraoperative i.v. dose administration of the anticomplement drug K76 instead of antibody depletion increased survival to 26 days. Although the events of kidney rejection were similar to those of heart xenografts and partially forestalled by the antibody inhibiting CP treatment, or by antibody depletion, survival for > 100 days was accomplished in only 5 of 86 treated animals. The poorer survival previously reported with cardiac xenotransplantation is largely explained by the life support requirement of the kidneys. Renal failure was responsible for almost all deaths before 60 days, and subnormal renal failure was a pervasive adverse factor thereafter, frequently caused by pyelonephritis which is suspected to have had an immunologic etiology.

Mimosine arrests DNA synthesis at replication forks by inhibiting deoxyribonucleotide metabolism

Mimosine has been reported to specifically prevent initiation of DNA replication in the chromosomes of mammalian nuclei. To test this hypothesis, the effects of mimosine were examined in several DNA replication systems and compared with the effects of aphidicolin, a specific inhibitor of replicative DNA polymerases. Our results demonstrated that mimosine inhibits DNA synthesis in mitochondrial, nuclear, and simian virus 40 (SV40) genomes to a similar extent. Furthermore, mimosine and aphidicolin were indistinguishable in their ability to arrest SV40 replication forks and mammalian nuclear chromosomal replication forks. In contrast to aphidicolin, mimosine did not inhibit DNA replication in lysates of mammalian cells supplied with exogenous deoxyribonucleotide triphosphate precursors for DNA synthesis. Mimosine also had no effect on initiation or elongation of DNA replication in Xenopus eggs or egg extracts containing high levels of deoxyribonucleotide triphosphates. In parallel with its inhibitory effect on DNA synthesis in mammalian cells, mimosine altered deoxyribonucleotide triphosphate pools in a manner similar to that reported for another DNA replication inhibitor that affects deoxyribonucleotide metabolism, hydroxyurea. Taken together, these results show that mimosine inhibits DNA synthesis at the level of elongation of nascent chains by altering deoxyribonucleotide metabolism.

[Cavernostomy and muscle plombage with the pedicled latissimus dorsi and serratus anterior flap for recurrent large bullae with infection: a case report]

A 70-year-old male, who suffered from infection by MRSA and Aspergillus of the recurrent large bullae, was operated on cavernostomy for space sterilization. About three months later he underwent muscle plombage with the pedicled latissimus dorsi and serratus anterior flap. These muscles are ideal to place in open wound in the thorax because of the following reasons: These have the ability to eliminate local infection, a sufficient length and volume to obliterate an open cavity. And transposition of these muscles cause minimal functional upper extremity disability. Therefore, we considered that this technic was useful for the case of an infectious intrathoracic cavity with many bronchial fistulas.

[A case of productive aspergilloma on the inner wall of a cavity, in which perbronchial fiberoptic bronchoscopy within the cavity was useful for the diagnosis and therapeutic evaluation]

A 45-year-old man complaining of bloody sputum was admitted. He had been treated for pulmonary tuberculosis since October 1988. He had bloody sputum in October 1989. His chest X-ray findings showed a cavitary lesion with a thickened and irregular wall in the right upper lobe. Fiberoptic bronchoscopy revealed white nodules on the cavity wall and the biopsy specimen from the nodule yielded a fungus granuloma. Aspergillus fumigatus was cultured from the sputum obtained after the bronchoscopy. Based on these findings, endobronchial aspergillosis and productive aspergilloma on the inner wall of a cavity was diagnosed. He was treated with oral anti-fungal drugs for 4 years. On chest X-ray films taken in June 1993, the cavity had enlarged, and the thickening and irregularity of the cavity wall had disappeared. Transbronchial fiberoptic bronchoscopy within the cavity showed whitish nodules and the cytology specimen obtained from the nodules by brushing yielded fungi, he was treated with oral itraconazol. Six months later, re-examination of the cavity revealed that the wall had become thinner and that the nodules on the inner wall had disappeared. This case illustrates the importance of bronchoscopy, in the diagnosis and evaluation of treatment of productive aspergilloma on the inner wall of a cavity.

Sensitization to cockroach allergens of asthma patients in Japan

To evaluate the role of allergens from Periplaneta fuliginosa, which is the most predominant cockroach species in homes in Tokyo areas, for asthma sensitization, we measured specific IgE antibodies to two cockroaches, P. fuliginosa and Blattella germanica, and to a mite, Dermatophagoides farinae, in 171 sera from children with asthma by Pharmacia's CAP system. We found that 16% of the sera had anti-P. fuliginosa IgE, whereas 9.9% had anti-B. germanica and 85% anti-D. farinae IgE. Further, we measured the levels of Per f I (Per a I equivalent) allergen in the house dust from living room, kitchen and bedding. We detected the allergen in eight of ten homes. The Per a I equivalent levels in kitchen were higher than in other sites, but they were much lower than Der I and Der II as Dermatophagoides allergens.

Molecular cloning of cDNA encoding human DNA helicase Q1 which has homology to Escherichia coli Rec Q helicase and localization of the gene at chromosome 12p12

A complementary DNA encoding DNA-dependent ATPase Q1 possessing DNA helicase activity, which is the major DNA-dependent ATPase in human cell extracts, was cloned from a cDNA library of human KB cells. The predicted amino acid sequence has seven consecutive motifs conserved in the RNA and DNA helicase super family and DNA helicase Q1 belongs to DEXH helicase family. A homology search indicated that helicase Q1 had 47% homology in the seven conserved regions with Escherichia coli RecQ protein. Three RNA bands of 4.0, 3.3, and 2.2 kilobases were detected in HeLa cells by Northern blotting. Analysis of the genomic DNA indicated the presence of a homologous gene in mouse cells. The DNA helicase Q1 gene was localized on the short arm of human chromosome 12 at 12p12.

Functional anatomy of taste perception in the human brain studied with positron emission tomography

Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) in 10 normal volunteers with the purpose of measuring rCBF changes related to taste physiology. Discrimination of 0.18% saline from pure water was associated with significantly increased rCBF values in the thalamus, the insular cortex, the anterior cingulate gyrus, the parahippocampal gyrus, the lingual gyrus, the caudate nucleus, and the temporal gyri. The results indicate that rCBF changes in these structures may reflect oral exposure to salt.

Combined immunosuppressive therapy with low dose FK506 and antimetabolites in rat allogeneic heart transplantation

Following rat heterotopic heart allotransplantation, low to lethal doses of the antimetabolites mizoribine (MIZ), RS-61443 (RS), and AZA were given alone or in combination with subtherapeutic doses of FK506 (0.04 mg/kg/day) for 14 days after transplantation. With the median effect analysis of Chou and Kahan for quantitative drug interactions, substantial therapeutic synergism was demonstrated between FK506 and non-toxic doses of MIZ (2.5, 5, and 10 mg/kg/day) or AZA (5, 30, and 45 mg/kg/day), which was particularly evident with the lowest dose MIZ (2.5 mg/kg/day). When FK506 was used in combination with MIZ or AZA but not with RS, the maximum effect (peak median graft survival) was enhanced significantly from 15 days (MIZ alone) to 26 days (P < 0.05), and from 19 days (AZA alone) to 32 days (P < 0.01). In contrast, RS interacted with FK506 no more than additively. Although RS was the most powerful single antimetabolite, the best overall survival was obtained by combining AZA and FK506. The addition of FK506 did not significantly increase the percent mortality and LD50 of the antimetabolites.