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The stable isotopes of sulfate, nitrate, and phosphate are frequently used to study geobiological processes of the atmosphere, ocean, as well as land. Conventionally, the isotopes of these and other oxyanions are measured by isotope-ratio sector mass spectrometers after conversion into gases. Such methods are prone to various limitations on sensitivity, sample throughput, or precision. In addition, there is no general tool that can analyze several oxyanions or all the chemical elements they contain. Here, we describe a new approach that can potentially overcome some of these limitations based on electrospray hyphenated with Quadrupole Orbitrap mass spectrometry. This technique yields an average accuracy of 1-2‰ for sulfate δ 34 S and δ 18 O and nitrate δ 15 N and δ 18 O, based on in-house and international standards. Less abundant variants such as δ 17 O, δ 33 S, and δ 36 S, and the 34 S- 18 O "clumped" sulfate can be quantified simultaneously. The observed precision of isotope ratios is limited by the number of ions counted. The counting of rare ions can be accelerated by removing abundant ions with the quadrupole mass filter. Electrospray mass spectrometry (ESMS) exhibits high-throughput and sufficient sensitivity. For example, less than 1 nmol sulfate is required to determine 18 O/ 34 S ratios with 0.2‰ precision within minutes. A purification step is recommended for environmental samples as our proposed technique is susceptible to matrix effects. Building upon these initial provisions, new features of the isotopic anatomy of mineral ions can now be explored with ESMS instruments that are increasingly available to bioanalytical laboratories.

The objective of the studies was to demonstrate that the contact sensitivity (CS) response to poison ivy/oak could be downregulated following treatment with a monoclonal antibody (mAb) reacting with the allergen urushiol. Conjugation of urushiol and its synthetic analogue 3-n-pentadecylcatechol (PDC) to N-acetylcysteine yielded hydrosoluble derivatives which induced humoral immune responses in BALB/c mice. Hybridomas secreting monoclonal antibodies (mAbs) reacting with urushiol and PDC were generated by fusion of B lymphocytes from immunized mice with mouse myeloma P3NS0 cells. The specificity of mAb ALG 991 (IgM isotype) was defined by inhibition of antibody binding by PDC analogues. This demonstrated that mAb ALG 991 reacted with the catechol moiety of urushiol, the region of the allergen being critically important in the induction of contact dermatitis. The CS response to urushiol in BALB/c mice was suppressed by stimulation with mAb ALG 991 and the role of sensitized T cells, including suppressor T cells, has been considered. Suppression of CS was most effective with low doses (1 microg) of mAb incorporated into a vaccine with Freund's adjuvant. This treatment suppressed CS responses in BALB/c mice already sensitized to urushiol.

The platelet P2T receptor plays a major role in platelet aggregation, and its antagonists are predicted to have significant therapeutic potential as antithrombotic agents. We have explored analogues of adenosine triphosphate (ATP), which is a weak, nonselective but competitive P2T receptor antagonist. Modification of the polyphosphate side chain to prevent breakdown to the agonist adenosine diphosphate (ADP) and substitution of the adenine moiety to enhance affinity and selectivity for the P2T receptor led to the identification of 10e (AR-C67085MX), having an IC50 of 2.5 nM against ADP-induced aggregation of human platelets. Compound 10e was the first very potent antagonist of the P2T receptor, with a selectivity for that subtype of the P2 receptor family of >1000-fold. Further modification of the structure produced compound 10l (AR-C69931MX) having an IC50 of 0.4 nM. In vivo, at maximally effective antithrombotic doses, there is little prolongation of bleeding time (1.4-fold), which is in marked contrast to the 5-6-fold found with GPIIb/IIIa antagonists.

Staff from four units for adults with profound learning disabilities described their relationship with a particular client during individual discussions. Issues arising from discussion were elaborated in subsequent individual and group meetings, evolving into an account of interactional aspects of professional care based on a core typology of relationships (Provider, Meaning-maker, Mutual and Companion). The process of this grounded theory analysis is exemplified. The analysis concludes with four propositions about staff-client relationships, and discussion of their implications for clinical services.

Attachment theory makes sense of two phenomena observed in some people with learning disabilities: it provides a reason for their limited exploration of the world, and it explains discontinuities in the pattern and intensity of their expressions of anger. Applying this framework to three enmeshed relationships occurring between an adult with learning disabilities and a member of care staff achieved at least partial resolution of their problems. Attachment theory's critics have set a number of challenges for its proponents, including emphasizing an interactional rather than a unidirectional approach to relationships; prioritizing social context; and understanding the attachment dynamic dimensionally rather than as a set of categories. The latter issue is pertinent for residential services: facilitating secure attachment relationships for distressed clients may be difficult for professionals, but partial assuagement of their attachment needs is a realistic clinical goal.

1. The role of endogenous ADP in platelet aggregation in vivo remains unclear due to the lack of suitable P2T-antagonist probes. This paper describes the potency, selectivity and specificity of the novel P 2T-purinoceptor antagonist, FPL 67085 (2-propylthio-D-beta,gamma-dichloromethylene ATP) both in vitro and in the anaesthetized rat in vivo. 2. FPL 67085 (3-30 nM) produced concentration-dependent rightward displacement of the concentration-effect (E/[A]) curve for ADP-induced aggregation of human washed platelets with no effect on ADP-independent aggregation at < or = 10 microM. 3. Logistic fitting of ADP E/[A] data indicated that the antagonist effect of FPL 67085 did not consistently accord with simple competition: in some preparations depression of the asymptote was seen. Schild analysis of data combined from all preparations, regardless of the antagonist profile observed, gave an apparent pKB of 8.9 (slope parameter 0.90). 4. The potency of FPL 67085 was unaffected by the P1-purinoceptor antagonist, 8-sulphophenyltheophylline, was similar (IC50 0.6-3.8 nM) in human and rat washed platelets or whole blood and, in rat blood, did not change following 2-30 min incubation at 37 degrees C. 5. FPL 67085 was a weak (pA50 approximately 4.2) partial agonist in tissues containing P2X- or P2Y-purinoceptors, indicating some 30,000 fold selectivity for the P2T-subtype. 6. In anaesthetized rats, intravenous infusion of FPL 67085 produced rapidly-reversible, dose-related inhibition of ADP-induced platelet aggregation measured ex vivo (ID50 1.3 micrograms kg-1 min-1) with no significant effect on haemodynamics or circulating cell counts. 7. Thus, FPL 67085 is a potent, specific and selective inhibitor of ADP-induced platelet aggregation both in vitro and in vivo. As such, it represents a novel pharmacological tool to define the role of endogenous ADP in thrombosis and the potential of P2T-purinoceptor antagonists as a novel class of infusible anti-thrombotic agents for acute use in man.

The effect on service provision of describing a variety of actions as challenging behaviour is discussed: it is suggested that studying stereotyped, aggressive and self-injurious acts in their own right has yielded more useful psychological debate, and ignoring such conceptual thinking leads to implicit theorizing where assumptions go unquestioned. Evidence for the relevance of staff actions on different topographies of client responses is critically reviewed, alongside discussion of the authors' rhetoric. The importance of adjusting language and frameworks to make room for alternative conceptualizations is discussed. The article concludes by recommending that research into staff attitudes and actions will be better served by reflexive methods and reporting which emphasize mutuality.

Moving from an individual to a social focus will allow clinical psychologists working with people who have learning disabilities to address a wider range of difficulties experienced by this client group. Social constructionist theory may be a useful framework to facilitate such an approach, and is intellectually compatible with changes occurring in other related disciplines. Research relevant to this perspective is reviewed under four subheadings proposed by Doise. Implications for clinical practice are discussed by reference to two case studies.

Balb/c mice treated with an immunotoxin constructed by conjugation of murine monoclonal antibody 791T/36 via a disulfide linker to ricin A chain generate a pronounced antibody response to peptide epitopes on ricin A chain. Monoclonal anti-RTA antibodies which recognize peptide epitopes have been developed and these have been used to down-regulate anti-RTA antibody responses in 791T/36-RTA immunotoxin-treated Balb/c mice. Of the five MAB tests, two (608/7 and 596/134) proved most effective, inhibiting anti-RTA antibody formation by up to 73%. MAB treatment was effective when initiated up to 3 days after immunotoxin treatment. Pharmacokinetic studies with 791T/36-RTA have shown that the immunotoxin is rapidly eliminated from the circulation, with no more than 4% remaining in blood after 24 hr. It is proposed that the down-regulation of anti-RTA antibodies is effected by MAB interfering with antigen processing.

Methotrexate (MTX) has been conjugated to various structurally related, synthetic, branched polypeptides containing a poly(L-Lys) backbone by the aid of water-soluble carbodiimide. The average degree of MTX incorporated was found to be dependent on the size of the polymer and on the identity of the terminal amino acid residue of the side chains. Consequently the average molar substitution ratio was in the range of 4.9-72.0 MTX per carrier molecule. CD spectra of conjugates showed significant differences in solution conformation correlating with the identity of the side-chain-terminating amino acid. Polycationic conjugates XAK-MTX (X = Leu or D-Leu) assumed essentially ordered (helical) secondary structure, while the CD spectrum of the amphoteric conjugate (X = Glu) corresponded to only a partially ordered conformation in PBS. The covalent attachment of MTX to branched polypeptides results in a reduction of drug in vitro cytotoxicity influenced by the carrier structure. Conjugation to amphoteric polymers, depending on the configuration and position of glutamic acid (XAK-MTX vs AXK-MTX type conjugates) resulted in a decrease of anti-791T cell activity. However polycationic conjugates bearing L-Leu at the side chain terminal position (LAK-MTX) produced a compound with cytotoxicity only about 60 times less effective than free MTX. The biodistribution in mice has been characterized by blood clearance, whole-body retention, and tissue distribution 24 h after iv administration. Blood clearance of MTX-branched polypeptides could be significantly prolonged by incorporation of glutamic acid into the side chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Daunomycin has been attached to various structurally related synthetic branched polypeptides with a polylysine backbone, using its acid-labile cis-aconityl derivative (cAD). Due to the importance of the side-chain structure in alpha-helix formation and immunological and pharmacological properties of branched polypeptides, we have investigated the conformation, biodistribution, and in vitro cytotoxicity of cAD-carrier conjugates with polypeptides containing amino acid residues of different identity and/or configuration at the side-chain end (XAK type) or at the position next to the polylysine backbone (AXK type), where X = Leu, D-Leu, Pro, Glu, or D-Glu. According to CD studies, polycationic conjugates with hydrophobic Leu in the side chains could assume a highly ordered conformation, while amphoteric conjugates containing Glu proved to be unordered in PBS. The reduction of in vitro cytotoxic activity of cAD by conjugation to carriers and the biodistribution profile of the conjugates were found to be dependent predominantly on the charge properties and on the side-chain sequence of the carrier polypeptide. It was demonstrated that by proper combination of structural elements of the carrier molecule, it is feasible to construct a cAD-branched polypeptide conjugate with significantly prolonged blood survival and with no reduction in in vitro cytotoxicity of the drug.

The difference between people with developmental disabilities who did and did not have peer-group friends was investigated by interviewing 36 adults attending day centers. Those with a friend were significantly more likely to describe themselves positively on all dimensions. Results showed that people without a peer-group friend were similar to lonely people without disabilities on two of the three factors explored. Qualitative analysis of subjects' descriptions of their friends suggested that most of the people interviewed had relatively shallow relationships.

Trichosanthin, a ribosomal inhibitor protein, blocks HIV replication in lymphocytes and macrophages. This agent was used to treat 51 patients with advanced HIV disease in a dose-escalation study in which three injections were administered over a 9-21-day period in a dose range of 10-30 micrograms/kg per injection. The maximum tolerated dose was estimated to be 30 micrograms/kg. Reversible but severe fatigue and myalgias were the major dose-limiting side-effects; mild leucocytosis and elevations in serum transaminases were noted and were reversible. Non-dose-related reversible mental status changes were seen in six patients and were considered to be associated with the drug. This was usually manifest as dementia, but progressed to coma in two patients. This reversed, but the sequelae resulted in death in one patient. Decreases in serum p24 antigen levels were noted 1 month after the first infusion in 10 of 18 patients who entered the study with elevated levels; one converted to negative. Values usually remained low to the end of the study period (2 months). In those patients with CD4+ cell levels greater than 50 x 10(6) cells/l significant decreases in sedimentation rate and increases in CD4+ cell numbers were also noted. These changes were found at all dose levels but only in patients receiving three infusions.

The biodistribution has been examined in mice of a range of synthetic branched polypeptides which are based on a polylysine backbone but which differ in ionic charge, side-chain structure, and molecular size. Polycationic polypeptides, regardless of their size or primary structure at the branches, were cleared rapidly from the circulation, the liver being the major site of clearance. Polypeptides with glutamic acid in the side chain, which would be amphoteric under physiological conditions, showed a significantly prolonged blood survival, and this was seen with polypeptides in the range of molecular weights of 46,000 up to 213,000. Such polypeptides provide a useful system with which to investigate the effect of structural parameters on the pharmacokinetic properties of carrier molecules and would allow the selection of candidate carriers for a variety of uses.

Surface components of Schistosoma mansoni have been identified by lactoperoxidasecatalyzed iodination. Cercariae have a simple labeling pattern in comparison to schistosomula. Transformation of cercariae to schistosomula results in the loss of a low molecular weight material which may be the glycocalyx, and the appearance of many more labeled proteins. Mechanical conversion of cercariae to schistosomula requires subsequent incubation at 37 degrees C for more than 1 h to give the full surface-labeling pattern of schistosomula. The majority of proteins found on schistosomula appear to be present throughout the remaining part of the developmental cycle, although adult male worms had only low levels of these antigens, and female worms had virtually no detectable surface antigens. The low level of expression of schistosome antigen could be caused by adsorbed host antigen, although no evidence for adsorbed host protein was found, or by a reduced level of antigens present on the worm surface. The low level of schistosome antigen could have a role in the resistance of adult worms to the host's immune response.

Metacercariae of Fasciola hepatica were excysted in a simple system based on the stimuli determined by Dixon (1966). Reproducibly high levels of excystment (70-80%) were obtained within 3h. Equal volumes of human serum and medium RPMI 1640 with 2% washed human red blood cells supported better growth in vitro than human serum diluted with ELac or NCTC 135. Reduced rates of growth were observed with serum concentrations lower than 50%. During culture over a period of 14 weeks some organisms in every culture grew to a length of 3 mm at a linear rate approximately one quarter of the growth rate in vivo (mouse). A few parasites suddenly began to develop more rapidly after six weeks in culture and reached 6-7 mm in length, comparable to the size of sexually mature Fasciola grown in mice. These cultured worms showed extensive development of the uterus, vitellaria, and testes with spermatozoa. The ovary remained rudimentary and egg formation did not occur.

The distribution in athymic nude mice of radiolabelled monoclonal antibody 791T/36 has been assessed during continuous infusion from subcutaneously implanted Alzet Osmotic Minipumps. During prolonged administration (up to 15 days) blood levels continued to rise. At 15 days, distribution of radiolabel was virtually identical to that seen after a single parenteral dose. Blood levels were in good agreement to those expected from whole body levels indicating satisfactory entry of antibody into the vascular compartment. Gel filtration chromatography of osmotic minipump contents and circulating radiolabel showed that the antibody had retained its structural integrity. In mice with human tumour xenografts examined a 5-day infusion of a mixture of 131I-791T/36 antibody and 125I-control IgG2b, blood levels of both radiolabels were comparable to those expected from whole body levels and there was effective tumour localization of the antibody to 2.5 times that of control IgG. These studies have demonstrated that prolonged administration of monoclonal antibody is feasible, that antibody enters the vascular compartment satisfactorily and that it can then localize in tumour deposits.

Very variable levels of immunity to a second infection with Schistosoma mansoni were recorded in 7 strains of mice, 12--15 weeks following a small primary infection. When 2 or more strains of mice were assayed at the same time, less variation occurred within the experiment than between different experiments. This evidence suggested variation between pools of cercariae as the main cause of variability in immunity. In direct experiments in one strain of mouse, 2 different pools of cercariae stimulated widely different levels of immunity to the same challenge. Conversely, challenge infections drawn from different pools showed different susceptibility to immunity stimulated by the same primary infection. Individual clones of cercariae, from snails infected with single miracidia, showed a high level of susceptibility to immunity stimulated by a small bisexual infection, or were not susceptible at all. Antigenic polymorphism is the most likely explanation for the differences observed between clones of cercariae. However, indirect immunofluorescence showed the presence of at least 1 common antigen on the surface of schistosomula derived from different clones of cercariae and clone-specific antigens have not been detected.

The biodistribution of radiolabelled methotrexate and immune complexes of methotrexate and a murine monoclonal anti-methotrexate antibody has been compared in mice. Complexes formed in-vitro with the antibody, but not with control immunoglobulin. The complexes were, characteristically, acid labile. In-vivo, blood levels, organ distribution and whole body catabolism of methotrexate in immune complexes were similar to those of free antibody, and markedly different from those of free drug. These findings suggest the feasibility of prolonging the survival of drugs and altering in-vivo distribution using complexes with monoclonal antibodies.

The maximum rate of development of Schistosoma haematobium in the hamster was determined by examination of the most advanced worms recovered at short intervals throughout the course of development. In culture S. haematobium developed at the same rate as in the hamster up to day 31 when pairing first occurs and male worms produce some spermatozoa. In vitro males formed some spermatozoa but pairing did not take place and, probably for this reason, females did not complete sexual maturation as occurs in the host between days 57-65. Somatic growth continued in vitro and at 70 days male worms had achieved almost the same length as in the hamster at this time. The culture medium, previously used for S. mansoni, consisted of equal volumes of serum and Earle's balanced saline with a final concentration of 0.25% lactalbumin hydrolysate, 100 units/ml penicillin, 100 mug/ml streptomycin and 1% rbc. The best culture results were obtained with one particular human serum; seven other human sera gave a wide range of growth support. The samples of baboon, rhesus monkey or foetal calf sera tested provided little or no growth support but prolonged survival was possible in all the sera.

We have investigated the actions of the coumarin anticoagulant, difenacoum, in male and female rats and mice. In our first experiment difenacoum (0.5 mg kg-1) killed 50% of male mice within 9 days of its administration, whereas no female mice died during this study. In a second group of experiments, the anticoagulant effect of difenacoum in male and female rats was determined. Under resting conditions, the prothrombin complex activities (PCA) of male and female rats were not significantly different. Over the first 24 h after administration of difenacoum (0.4 mg kg-1 i.p.), there was a monoexponential fall in PCA in both sexes. However, 6, 12 and 24 h after difenacoum, the PCA in male rats was significantly (P less than 0.05) lower than in female rats. PCA began to recover over the subsequent 48 h in both sexes, during which time there was marked variability in recovery in female rats. The difference between the onset of action of difenacoum in male and female rats did not appear to be due to a greater rate of elimination of the drug in female rats, since the plasma concentrations of difenacoum 24 h after its administration were the same in both sexes. The concentration of vitamin K1 in rat liver was also investigated. Vitamin K1 levels were 35.1 +/- 18.6 ng (g liver)-1 (male), and 29.4 +/- 5.4 ng (g liver)-1 (females) in control rats, but 24 h after difenacoum, vitamin K1 levels were either very low, or undetectable in all rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Two surface antigens were isolated from young or adult schistosomes by affinity chromatography with monoclonal antibodies. Vaccination with an antigen having a molecular weight of 155,000 gave partial protection against challenge in some batches of mice and in a group of cynomolgus monkeys. Vaccination with an antigen having a molecular weight of 53,000 gave similar levels of protection in mice. The results demonstrate that protection can be obtained with single antigens, but the precise requirements for reproducible vaccination are as yet unknown.

Young schistosomes collected after penetration through isolated mouse skin (3 h schistosomula) were cultured in medium containing immune rhesus monkey serum with a high titre of antibody known to kill schistosomula in the presence of complement. Morphological signs of damage in electron micrographs were confined to the surface tegument of the schistosomula. Antibodies in immune rhesus serum were shown to bind to the surface membrane of 3 h schistosomula using an antibody-enzyme bridge technique involving labelling with horseradish peroxidase and histochemical localization of the enzyme at the ultrastructural level. Schistosomula recovered from the lungs of mice 4 days after infection did not bind monkey antibodies at the surface and these 4-day schistosomula are not susceptible to damage by immune serum in vitro. Mouse erythrocyte antigens were detected on the surface of 4-day schistosomula using an appropriate antibody-enzyme bridge but these host antigens could not be found on 3 h schistosomula. This correlation between the presence of mouse host antigens on the surface of schistosomula and the inability of immune monkey antibodies to bind to the surface membrane is consistent with the hypothesis that host antigens are acquired by young schistosomes and serve to protect the surface membrane against antibody-mediated damage.

Previous work has demonstrated wide variation in the susceptibility of different clones of Schistosoma mansoni to resistance in mice induced by a small schistosome infection. Eight monoclonal antibodies directed against individual surface antigens of juvenile schistosomes (schistosomula) were used to determine the distribution of these antigens among clones of schistosomula. All eight antigens were detected on the surface membranes of the 32 clones of schistosomula tested. This result implies that polymorphism of schistosomula surface antigens is very unlikely to be the cause of the variation in susceptibility of different clones to resistance in mice. Absence of heterogeneity among surface antigens of schistosomula may facilitate experimental vaccination aimed against these putative target antigens.

Hamsters (WO strain) with a primary infection of Schistosoma mansoni or S. haematobium rapidly developed immunity to homologous challenge judged by the lung recovery assay. Immunity was detected at 4-5 weeks and reached a plateau 6 weeks after infection. Using this information, hamsters with an 8-week primary infection with S. mansoni or S. haematobium were tested for resistance to homologous reinfection and resistance to a challenge with the other species of schistosome. Primary infection with S. mansoni or S. haematobium conferred a high level of immunity to reinfection with either species of schistosome judged by the perfusion assay, involving recovery of adult worms 6-10 weeks following challenge. Estimation of the level of immunity with the lung recovery assay, 5 days after challenge, indicated that immunity due to a primary infection with S. mansoni acted at or before migration of the challenge through the lungs but immunity stimulated by a primary S. haematobium infection was only partially effective at the lung stage and substantial destruction of challenging organisms occurred at a later stage of development. Antibodies in immune sera of hamsters with a primary S. mansoni or or S. haematobium infection were shown to bind to common antigens on the surface of young schistosomula of either species by u.v. microscopy using as detecting agent a fluorescein-labelled rabbit antiserum directed against hamster globulins.

The level of resistance induced by a single percutaneous infection of cercariae which had been previously exposed to 20 kr of gamma irradiation was compared in two strains of mice. Challenge cercariae were given at several time intervals after the preliminary immunization either to the same skin site as that used for immunization or to a previously unexposed skin site. No significant difference in resistance to infection was observed when a different skin site was used for the challenge. A higher degree of resistance to challenge was observed in CBA/Ca mice than in BALB/c mice. Immunity in both strains declined to about two thirds of the original level after six months and could not be detected when challenge cercariae were given 70 weeks after the single immunizing dose of irradiated cercariae.

A primary infection with schistosoma mansoni, of 5 or more weeks duration, stimulated a high level of resistance to a challenge infection in the WO outbred strain of golden hamster. In sharp contrast, the LGN strain showed no statistically significant immunity to reinfection in most experiments and where detected the level of resistance was only about half that observed in the WO strain. Immunity to reinfection was assayed with the lung recovery method which assesses resistance a few days after challenge and with the conventional perfusion assay which measures immunity 6 weeks after challenge. Wide differences in the immune response to S. mansoni in different strains of the same host species have not been reported previously.

Two hybridomas secreting monoclonal IgM antibody to Schistosoma mansoni have been isolated following fusion of spleen cells from Balb/c mice immunized with living S. mansoni and NS1 myeloma cells. One monoclonal IgM antibody (WP66.4) mediated about the same level of passive protection against a challenge infection as immune serum from mice with a chronic S. mansoni infection. The other monoclonal antibody (WP66.2) did not give a significant level of passive protection. This result indicates that the effective monoclonal antibody recognizes an antigen which may be a valuable candidate for experimental vaccination. In vitro one monoclonal antibody (WP66.4) caused a much higher level of complement-dependent cytotoxicity than the other (WP66.2), suggesting a possible mechanism for the effect observed in vivo. With indirect immunofluorescence both monoclonal antibodies reacted with surface determinants on living S. mansoni schistosomula, adult worms and miracidia but these determinants were not detected on cercariae or lung schistosomula. Neither monoclonal antibody cross-reacted with S. haematobium schistosomula or Fasciola hepatica metacercariae, indicating a possible use for these reagents in differential diagnosis of S. mansoni infections.

Juvenile forms of Schistosoma mansoni (schistosomula) have been cultured in human blood of various specificities and tested for the presence of blood group substances on their surfaces. The tests employed were survival following transfer into rhesus monkeys immunized against human blood substances, mixed agglutination reactions, and immunofluorescence. A, B, H AND Lewisb+ antigens were expressed at the surface when the parasites were cultured in blood of appropriate specificities. Rhesus, M N S, AND Duffy antigens could not be detected on the parasite surface following culture. The evidence suggests that the expressed blood group antigens are of host origin and are acquired by the parasite during culture, probably in the form of glycolipids or megaloglycolipids. It is likely that these substances are also acquired by parasites in the bloodstream of man. They may serve to mask surface parasite antigens, and so enable schistosomes to evade parasite-specific humoral or cellular immune responses.

The blood kinetics and tumour localization of a conjugate of methotrexate (MTX) and MAb 791T/36 were examined in nude mice with human tumour xenografts. The antibody moiety of the conjugate was detected by labelling with 125I and the drug moiety was assayed using a radioimmunoassay for methotrexate. After radioiodination, the drug moiety was co-precipitable with the radiolabel when TCA or rabbit anti-mouse IgG antiserum was used. Following i.v. injection, serum kinetics of both the antibody and the drug moieties of the conjugate were essentially similar, and the integrity of serum-borne conjugate was confirmed by the co-precipitation of radiolabel and drug. The radiolabelled antibody moiety of the conjugate localized in tumour xenografts, with 5-7% of the injected dose being present per gram of tissue within 6 hr of injection, and the levels were maintained for up to 4 days. Analysis of tumour levels of the MTX moiety showed a progressive uptake over the 4-day observation period with up to 4% of the injected dose being present per gram of tumour when the experiment was terminated. Parallel studies with free MTX showed rapid clearance from the blood and a maximum of 0.35% of the dose/g of tumour 30 min after injection. Control immunoglobulin conjugated to MTX did not show tumour localization of either the antibody or the drug moieties. These studies confirm that in vivo MTX remains bound to antibody in this type of drug antibody conjugate and demonstrate site-specific targeting of this therapeutic agent.

The monoclonal antibody (MAb) 791T/36 which has previously been shown to localise in colorectal cancer has been conjugated to methotrexate (MTX) for potential use as a chemotherapeutic agent in malignant disease. To examine its biodistribution and tumour localisation, 16 patients with primary colorectal cancer were injected intravenously with 131I-labelled 791T/36-MTX conjugate and imaged using a gamma camera after 48-72 hr. Serial blood samples were taken to determine the levels of circulating conjugate and samples of tumour and normal colon were assayed for uptake of radioactivity. Whole body biodistribution, visualised by gamma scintigraphy, and blood clearance of both the antibody and drug moieties of 791T/36-MTX were similar to that previously found with unconjugated antibody. Assays of tissue radioactivity showed positive tumour uptake of drug-antibody conjugate (T:NT greater than 1.9:1) in 13/15 primary tumour specimens (median T:NT = 2.9:1). These studies indicate that 791T/36-MTX conjugates may have potential in the treatment of metastatic colorectal carcinoma.