Comparison of the performance of anti-CD7 and anti-CD38 bispecific antibodies and immunotoxins for the delivery of saporin to a human T-cell acute lymphoblastic leukemia cell line

We have investigated the cytotoxic performance of two different anti-CD7/anti-saporin BsAb's (HB2 x DB7-18 and Q1.1), three anti-CD38/anti-saporin BsAb's (OKT10 x RabSap, OKT10 x DB7-18 and Q4.1) and an anti-CD7 (HB2-Sap) and anti-CD38-saporin (OKT10-Sap) immunotoxin for delivering the ribosome inactivating protein (rip) to the human T-cell acute lymphoblastic leukemia cell line HSB-2. In the case of CD7 as target molecule the immunotoxin outperformed both anti-CD7 BsAb's being six times more effective than HB2 x DB7-18 and 98 times more so than Q1.1 at effectively inhibiting protein synthesis in a dose dependent manner. The chemically constructed HB2 x DB7-18 BsAb was more effective at inhibiting protein synthesis and cell growth in target HSB-2 cells in a dose dependent manner than the quadroma produced BsAb Q1.1. Both BsAb demonstrated a prozone effect used at concentrations above 0.1 nM though this was more pronounced for Q1.1 than for HB2 x DB7-18. The prozone effect was partially though not completely reversed by increasing the concentration of saporin in the system. In the case of CD38 as target molecule the anti-CD38 IT OKT10-Sap performed poorly, never actually achieving its IC50. Two BsAb's constructed with monoclonal anti-saporin Fab arms each recognizing a different epitope on the saporin molecule also performed poorly. In contrast the BsAb OKT10 x RabSap constructed with Fab derived from a rabbit polyclonal anti-saporin antiserum performed in a dose dependent manner achieving its IC50 at a concentration of 1.3 nM. This BsAb also exhibited a prozone effect. These results exemplify the importance of cross linking adjacent target molecules on the cell surface in order to achieve effective delivery of saporin to the cell interior.

Glycosylation patterns of the human colon cancer cell line HT-29 detected by Helix pomatia agglutinin and other lectins in culture, in primary tumours and in metastases in SCID mice

Human colonic cancer cells (HT-29, 10(7) cells/dose) were injected subcutaneously between the scapulae of 19 severe combined immunodeficient (SCID) mice. After 19 days, large tumours had developed in 18 out of the 19 animals and the mice were then killed. Metastases were detected in the lungs of 16 animals but not in other organs investigated. Surgical removal of the primary tumour in another group of five animals led to a prolonged survival and further growth of metastases in the lungs. HT-29 injection into the tail vein (n = 5) resulted in colonization of the lungs. The tumours that developed in the animals were signet cell carcinomas; these forms are not seen in HT-29 cells in culture. Glycoconjugate expression of the tumours was assessed using several lectins. In many cases the results indicated a stability of lectin-binding patterns from cell culture conditions to implantation into the SCID mice. This was true for the lectin Helix pomatia agglutinin (HPA), the binding of which is associated with a high metastatic potential in some human tumours, including colon cancer. All the primary tumours and metastases were HPA positive. This xenograft tumour model seems to be a clinically relevant system for the study of glycoconjugate expression in human colon cancer cells and their metastases.

Therapy of human T-cell acute lymphoblastic leukaemia in severe combined immunodeficient mice with two different anti-CD7-saporin immunotoxins containing hindered or non-hindered disulphide cross-linkers

A SCID mouse model of human T-ALL has been used to determine the in vivo therapeutic efficacy of two anti-CD7-saporin immunotoxins constructed with either a hindered (HB2-SMPT-Sap) or non-hindered (HB2-SPDP-Sap) disulphide bond between antibody and saporin. Groups of 10 SCID mice were injected intravenously (i.v.) with 2 x 10(6) human T-ALL HSB-2 cells followed seven days later by i.v. injection with either a single dose or with 3 doses of HB2-SPDP-Sap or HB2-SMPT-Sap given on alternate days. Control groups received equivalent sham injections of PBS or molar equivalent amounts of unconjugated HB2 antibody+saporin. Animals receiving a single dose of HB2-SMPT-Sap showed better survival than animals receiving a single dose of HB2-SPDP-Sap but the difference was not shown to be significant by log-rank analysis. When given as a triple dose both immunotoxins performed similarly. Comparison of single-dose with triple-dose IT therapy revealed that the therapeutic effect of a triple dose of HB2-SPDP-Sap was significantly better than that of single dose, but this was not the case with HB2-SMPT-Sap. Pharmacokinetic studies of HB2-SPDP-Sap and HB2-SMPT-Sap in normal and HSB-2 leukaemia bearing SCID mice failed to reveal any difference in clearance rates for these two IT's. We conclude from these studies that there is no therapeutic advantage to be gained from constructing the HB2-Sap IT with a hindered disulphide bond in this particular model of human T-ALL.

Effectiveness of HB2 (anti-CD7)--saporin immunotoxin in an in vivo model of human T-cell leukaemia developed in severe combined immunodeficient mice

The transplantation of the human T-cell acute lymphoblastic leukaemia (T-ALL) cell line HSB-2 into severe combined immunodeficient (SCID) mice was found to produce a disseminated pattern of leukaemia similar to that seen in man. The intravenous injection of 10(7) HSB-2 cells was associated with a universally fatal leukaemia. Histopathological examination of animals revealed the spread of leukaemia initially from bone marrow to involve all major organs including the meninges. An immunotoxin (HB2-Sap) was constructed by conjugating the anti-CD7 MAb HB2 to the ribosome-inactivating protein saporin. An in vitro protein synthesis inhibition assay revealed specific delivery of HB2-Sap immunotoxin (IT) to CD7+ HSB-2 target cells with an IC50 of 4.5 pM. When SCID mice were injected with 10(6) HSB-2 cells and then treated 8 days later with a single intravenous dose of 10 micrograms of immunotoxin there was a significant therapeutic effect evidenced by the numbers of animals surviving in the therapy group compared with untreated controls (chi 2 = 5.348, P = 0.021). These results demonstrate the useful application of human leukaemia xenografts in SCID mice and the potential therapeutic effect of an anti-CD7 immunotoxin in human T-ALL.

Immunotoxin studies in a model of human T-cell acute lymphoblastic leukemia developed in severe combined immune-deficient mice

The transplantation of the human T-cell acute lymphoblastic leukemia (T-ALL) cell line HSB-2 into severe combined immune-deficient (SCID) mice was found to produce a disseminated pattern of leukemia similar to that seen in humans. The iv injection of 10(7) HSB-2 cells was associated with a universally fatal leukemia. Histopathological examination of animals revealed the spread of leukemia initially from bone marrow to involve all major organs including the meninges. An immunotoxin (HB2-Sap) was constructed by conjugating the anti-CD7 monoclonal antibody (MAb) HB2 to the ribosome inactivating protein (RIP) saporin. An in vitro protein synthesis inhibition assay revealed specific delivery of HB2-Sap immunotoxin (IT) to CD7+ HSB-2 target cells with an IC50 of 4.5 pM. In an in vivo study, the IT was shown to significantly prolong the survival of SCID mice injected with HSB-2 cells compared to untreated control animals. This therapeutic effect was seen both with a single injection of 10 micrograms of IT given 7 d after the injection of HSB-2 cells, and was even more effective when IT was administered as three daily injections of 10 micrograms on d 7, 8, and 9. These results demonstrate the useful application of human leukemia xenografts in SCID mice and the potential therapeutic effect of an anti-CD7 IT in human T-ALL.

Effectiveness of combinations of bispecific antibodies for delivering saporin to human acute T-cell lymphoblastic leukaemia cell lines via CD7 and CD38 as cellular target molecules

We have investigated the effectiveness of three different F(ab' gamma)2 bispecific antibodies (BsAb) for delivering the ribosome inactivating protein (RIP) saporin via the CD7 or CD38 cell surface molecules to the human T-ALL cell lines HSB-2 and HPB-ALL. Inhibition of 3H-leucine uptake by target cells was used as the parameter of cellular cytotoxicity. Used singly against HSB-2 cells in the presence of varied concentrations of saporin, an anti-CD7 BsAb, (HB2 x DB7-18) and an anti-CD38 BsAb (OKT10 x RabSap), gave 435- and 286-fold increases in saporin toxicity, respectively. For HPB-ALL cells the anti-CD7 BsAb performed poorly giving only an eight-fold increase in toxicity whilst on the same cell line the anti-CD38 BsAb was highly potent giving an 80,000-fold increase in saporin toxicity. A combination of both BsAb used together against HSB-2 cells was ten times more effective, than the best single BsAb HB2 x DB7-18 used alone. Kinetic studies conducted with HSB-2 cells revealed that the BsAb combination also gave an increased rate of protein synthesis inactivation in comparison to either BsAb used alone. These investigations clearly demonstrate a synergistic action when both BsAb are used in combination to target saporin against CD7 and CD38 expressed on the surface of the HSB-2 cell line.

High-dose mitoxantrone and etoposide conditioning in autologous bone marrow transplantation for relapsed Hodgkin's disease

We administered high-dose mitoxantrone in combination with etoposide to 6 patients with relapsed Hodgkin's disease as the conditioning regimen for autologous bone marrow transplantation. This regimen was well tolerated and no significant cardiotoxicity was observed. Responses of the Hodgkin's disease to this therapy were favourable but short-lived. Serial measurements of the serum levels of mitoxantrone suggested an open 3-compartment model of drug distribution. The rapid early phase of drug distribution was followed by an intermediate phase and a slow terminal drug-elimination phase. However, mitoxantrone was still detected in the serum of all patients 7 days after the last dose of mitoxantrone and on the day of bone marrow re-infusion. The clinical significance of such findings is unclear but they may suggest a need for the use of other anthracycline-related cytotoxic agents for the conditioning in autologous bone marrow transplantation.

Characteristics and performance of a bispecific F (ab'gamma)2 antibody for delivering saporin to a CD7+ human acute T-cell leukaemia cell line

We have investigated the efficacy of a F(ab'gamma)2 bispecific antibody (BsAb) with dual specificity for the CD7 molecule in one Fab arm and for the ribosome inactivating protein (rip) saporin in the other arm, for delivering saporin to the acute T-cell leukaemia cell line HSB-2. Saporin titration experiments revealed that BsAb increased the toxicity of saporin 435-fold for HSB-2 cells, reducing the IC50 for saporin alone from 0.1 mumol to 0.23 nmol when BsAb was included. The rate of protein synthesis inactivation brought about by BsAb-mediated toxin delivery to HSB-2 cells was very similar to that described for conventional immunotoxins (IT's) with a t10 (time taken for a one log inhibition of protein synthesis compared with controls) of 46 h obtained at a saporin concentration of 1 nmol and 226 h at 0.1 nmol. BsAb titration studies demonstrated a clear dose response effect of BsAb concentration on target cell protein synthesis inhibition and cell proliferation. The absolute specificity of toxin delivery was unequivocally demonstrated by a failure of BsAb to deliver an effective dose of saporin to the CD7- cell line HL60 and by the blocking of BsAb-mediated delivery of saporin to HSB-2 cells with an excess of F(ab)2 fragments of the anti-CD7 antibody, HB2. These studies have clearly demonstrated the effectiveness of this BsAb for delivering saporin to a T-ALL cell line utilising CD7 as the target molecule on the cell surface. BsAb's would therefore appear to offer a realistic alternative to IT's for toxin delivery to tumour cells and may even offer certain advantages over conventional IT's for clinical use.

The anti-mitozantrone monoclonal antibody NO-1, protects acute leukaemia cell lines from the cytotoxic effects of mitozantrone

The monoclonal antibody NO-1 was raised against the potent anti-cancer drug mitozantrone by immunization of a BALB/c mouse with a mitozantrone-keyhole limpet haemocyanin conjugate in Freund's complete adjuvant. This antibody was shown to be highly effective in vitro at neutralizing the cytotoxic effects of mitozantrone for the acute leukaemia cell lines ALL-1 and MOLT4. In order to achieve complete protection, a drug to antibody molar ratio of 1.5:1 was required. The neutralizing effect was specific for mitozantrone, as NO-1 antibody offered no protection of the MOLT4 cell line to the cytotoxic effects of the anthracycline drug daunorubicin when used at a near identical molar ratio. NO-1 antibody has already proven a highly successful monoclonal reagent for use in a competitive enzyme-linked immunosorbent assay for the accurate and sensitive quantitation of mitozantrone in serum. The neutralizing properties of NO-1 suggest other possible applications for this antibody. These could include a use in the rapid clearance of pharmacologically active mitozantrone from the circulation following very high dose administration prior to bone marrow transplantation and for the construction of bispecific antibodies for targeting mitozantrone to tumour cell populations.

Molecule detected in formalin fixed tissue by antibodies MT1, DF-T1, and L60 (Leu-22) corresponds to CD43 antigen

Three monoclonal antibodies MT1, L60 (Leu-22), and DF-T1, were reported independently as recognising human T cells in routinely processed, paraffin wax embedded tissue. The present study was performed to compare these three reagents in terms of their immunocytochemical reactions and target molecule(s). On Western blotting of white cell extracts the three antibodies reacted with antigens of the same molecular weight (range 110-160 kilodaltons). Furthermore, their immunocytochemical reactivity with normal human cells, as analysed by two-colour flow cytometry, was essentially identical (labelling of monocytes, most T lymphocytes, and weak reactions with some B cells), and the antibodies gave closely similar reactions on 54 white cell derived neoplasms. To identify the target antigen for these three reagents, antibodies from the Third International Workshop on Leucocyte Antigens were reviewed and it was shown that the Western blotting and immunocytochemical reactions of MT1, L60 (Leu-22), and DF-T1 were identical with those of the reagents which defined the CD43 antigen (also known as leucosialin or sialophorin). Furthermore, all these antibodies reacted with cells transfected with a cDNA clone encoding CD43. It is concluded that antibodies MT1, L60 (Leu-22), and DF-T1 all recognise the heavily glycosylated myeloid/lymphoid associated CD43 antigen.

Identification of peanut agglutinin binding glycoproteins restricted to Hodgkin's disease-derived cell lines

Peanut agglutinin (PNA) binding glycoproteins from four Hodgkin's disease (HD)-derived cell lines and a variety of cell lines/peripheral blood cells representative of the lymphoid and myeloid lineages were identified by probing nitrocellulose membranes of SDS-PAGE separated NP40 solubilized cellular glycoproteins with [125I]-labelled PNA. The two Hodgkin's cell lines Ho and L428 demonstrated the most heterogeneous glycoprotein profiles each expressing 15 PNA binding glycoproteins, respectively. The two remaining Hodgkin's lines Co and L591 expressed only four glycoproteins each and these were all also commonly expressed by Ho and L428. Comparative analysis with all other cell types studied revealed the expression of five glycoproteins restricted to Ho (gp42, gp40, gp38, gp24 and gp22) and six restricted to L428 (gp180, gp75, gp40, gp38, gp24 and gp22). Four of these, gp40, gp38, gp24 and gp22 were commonly expressed by both Ho and L428. Of cell lines of myeloid lineage studied only the erythroleukemia cell line K562 expressed detectable glycoproteins also expressed by some of the Hodgkin's cell lines (gp110, gp96, gp50 and gp45). Only one glycoprotein, gp20 expressed by Ho was also commonly expressed by normal peripheral blood granulocytes. This limited study has thus succeeded in demonstrating for the range of cell types studied, that some glycoproteins with terminal D-galactose beta (1----3) N-acetyl galactosamine oligosaccharide sequences are apparently restricted to two of the HD cell lines. Moreover, the heterogeneous glycoprotein profiles obtained for the HD cell lines Ho and L428 suggests that galactosylation processes in these two cell lines is aberrant.

The Reed-Sternberg cell/lymphocyte rosette. I. Properties of rosettes formed between Hodgkin's cell lines and allogeneic lymphocytes

The properties of rosettes formed between the Hodgkin's cell lines, L428 and L591, and allogeneic peripheral blood mononuclear cell populations have been investigated. Immunocytochemical analysis showed that the majority of adherent cells were T-cells of both the CD4 and CD8 subsets. Only relatively few B-cells and monocytes were seen to adhere. However, when peripheral blood mononuclear cell populations were fractionated, it was found that monocytes were as good as T-cells at forming rosettes with both L428 and L591, though B-cells were shown to be poor at forming such associations. Treatment of both L428 and L591 with neuraminidase resulted in a significant reduction (P less than 0.01) in the mean number of adherent lymphocytes and in the numbers of Hodgkin's tumour cells which formed rosettes. Smaller, less significant effects were observed for Cytochalasin B and trypsin. EDTA (10(-2) M) at pH 7.2 had no significant effect on rosetting for L428 or L591. Adherence of allogeneic lymphocytes to L428 or L591 was pH dependent but did not appear to correlate with cell surface charge. Treatment of L428 cells with Fab fragments prepared from the IgG fraction of a hyperimmune rabbit anti-L428 antiserum, significantly (P less than 0.05) inhibited the adherence of allogeneic lymphocytes, but only when used at high concentration. The binding requirements of the Hodgkin's cell lines with allogeneic peripheral blood lymphocytes, as described in this study, appear to be quite different from those described for freshly isolated Hodgkin's tumour cells with autologous intratumoral lymphocytes. This suggests that the two phenomena may be unrelated. There would appear to be an absolute requirement for cell surface sialic acid for allogeneic lymphocyte attachment to the HD cell lines. This might suggest that the receptor-ligand system involved contains sialic acid as an integral part of the cell surface receptor structure involved in recognition of the appropriate ligand.

Development of a sensitive monoclonal antibody-based enzyme-linked immunosorbent assay (ELISA) for mitozantrone

A mouse monoclonal antibody (NO-1) with specificity for the anti-cancer drug mitozantrone (MZ) (Novantrone) was produced by immunization of a BALB/c mouse with mitozantrone-keyhole limpet haemocyanin (MZ-KLH) conjugate. When used in an indirect competitive enzyme-linked immunosorbent assay (ELISA), NO-1 permitted the accurate and reproducible detection of between 0.25-50 ng/ml of MZ in pooled human serum, the standard curve obtained within this range being virtually linear. The assay demonstrated good reproducibility with intra-assay coefficients of variation (CV) of between 1.41% and 7.02% and an inter-assay CV of 3.45%. Regression analysis of levels of MZ detected by ELISA vs. the actual amounts added to pooled human serum gave a very good correlation coefficient of r = 0.995. NO-1 showed no cross-reactivity with either bisantrene or daunorubicin. A simple pharmacokinetic study was undertaken in rabbits given MZ intravenously at a dose of 0.5 mg/kg of body weight. Levels of MZ in rabbit serum measured with the assay ranged between 82 and 170 ng/ml for rabbits 1 and 2, respectively at 15 min falling to 1.25 ng/ml by 48 h for rabbit 1 and falling to undetectable levels by 120 h for rabbit 2.

Mac 387 antibody and detection of formalin resistant myelomonocytic L1 antigen

The murine monoclonal antibody Mac 387 was raised against a purified protein fraction obtained from human monocytes. By immunoblotting experiments, Mac 387 was shown to react with a previously defined antigen called L1; this is a multichain myelomoncytic protein of about 36 Kd which shows sequence homology with the cystic fibrosis antigen. The L1 protein is present in the cytoplasm of virtually all resting peripheral neutrophils and monocytes; it is also variably expressed on the plasma membrane of these cells, possibly as a secretory product. Because the L1 antigen is resistant to denaturation by formalin, its tissue distribution can be studied in routinely processed biopsy material. In a wide variety of specimens Mac 387 was shown by immunohistochemical analysis, to produce a cytoplasmic staining pattern concordant with that of a well defined polyclonal antibody to the L1 antigen. Cytoplasmic reactivity was obtained with granulocytes and infiltrating macrophages but generally not with several categories of dendritic cells. In addition, squamous epithelium of mucous membranes was strongly positive, in contrast to normal epidermis.

Identification of tissue histiocytes on paraffin sections by a new monoclonal antibody

A mouse monoclonal antibody (MAC 387) with specificity for monocytes and tissue histiocytes was produced by immunization of a BALB/c mouse with peripheral blood monocyte components derived by affinity chromatography of detergent-solubilized monocyte material on Sepharose 4B coupled to rabbit anti-monocyte antibodies. MAC 387 strongly stained the cytoplasm of cells of the monocyte/macrophage series on paraffin sections after controlled trypsinization of sections. The antibody showed broad reactivity for a variety of tissue histiocytes, including infiltrating and reactive histiocytes, alveolar macrophages, Kupffer cells, follicle-center macrophages, splenic red pulp macrophages, tumor-infiltrating macrophages, sinus histiocytes, epithelioid giant cells (variably), and cases of histiocytosis X and dermatopathic lymphadenopathy. Molecular weight data obtained by Western blotting, immunoprecipitation, and immunoaffinity-purification revealed that the antigen was present in different forms in the monocyte and granulocyte. In the granulocyte, free alpha (Mr 12 KD) and beta (Mr 14 KD) chains expressing the MAC 387 epitope were found together with associations of one alpha and one beta chain linked by disulfide bonds to yield a heterodimer of Mr 26 KD. In the monocyte, free alpha and beta chains are not found, but instead the heterodimer and associations of two (Mr 56 KD) and four (Mr 112 KD) heterodimers are disulfide-linked together. This new monoclonal reagent should have particular value for identification of tissue histiocytes in routine paraffin sections and particularly for demonstration of histiocytes in malignant lymphomas.

Opisthorchis viverrini: pathogenesis of infection in immunodeprived hamsters

Opisthorchis viverrini infections were established in immunologically intact and T cell deprived hamsters. T cell deprivation appeared to have no effect on worm establishment or egg production. Histopathologically, intact and deprived animals showed similar degrees of bile duct hyperplasia and periductular fibrosis, though there was a marked reduction in the intensity of the periportal inflammation in the majority of T cell deprived animals. Serum transaminase levels were significantly raised in intact animals by 25 days after infection, whilst levels remained within normal limits throughout the infection period for the majority of the T cell deprived animals. The antibody response to parasite antigens as determined by immunoelectrophoresis, was impaired in T cell deprived animals. Attempts to correlate the serological picture with transaminase levels at three time points after infection and also with the extent of periductular inflammation seen on killing, proved largely unsuccessful. These results indicate that T cell deprivation of the hamster host ameliorates the periductular inflammatory response provoked by O. viverrini in this species. It is suggested that such inflammatory responses are evoked by parasite antigens which gain access to portal tract and surrounding areas, and that such reactions are immunopathological in their outcome to the host, resulting in liver cell death and subsequent replacement of resolving inflammatory and necrotic areas with fibrotic tissue.

Promotion of N-nitrosodimethylamine-initiated bile duct carcinogenesis in the hamster by the human liver fluke, Opisthorchis viverrini

Four groups of male golden Syrian hamsters were treated as follows: Group I received 50 Opisthorchis viverrini metacercariae followed 41 days later by a single oral dose of 1.6 mg N-nitrosodimethylamine (NDMA). Group II received a single oral dose of 1.6 mg NDMA followed 96 h later by 50 O. viverrini metacercariae, Group III received a single oral dose of 1.6 mg NDMA only and Group IV 50 O. viverrini metacercariae only. Mortality was highest in Group I and II animals receiving both NDMA and parasites. Cholangiocarcinomas were discovered in five animals from Group I and in nine animals from Group II representing tumour incidences of 10% and 20%, respectively. None of the animals given NDMA alone (Group III) or parasites alone (Group IV) developed malignant bile duct tumours. The mean tumour latency period for Group I was 249 days (range 124--346 days) and for Group II 308 days (range 184--393 days). The difference for tumour latency between these two groups was not significant. Tumour was most frequently found in the right liver lobe, the lobe in the hamster which also contains the largest proportion of infecting O. viverrini worms. These results clearly indicate that an O. viverrini infection in the hamster host is capable of promoting NDMA-initiated bile duct carcinogenesis. These observations may bear some direct relevance to cholangiocarcinoma arising in association with Oriental liver fluke infection in man and may provide a useful tool for the study of an initiation-promotion system of aetiological significance for man.

Opisthorchis viverrini: the relationship between egg production, worm size and intensity of infection in the hamster

Worm recoveries, egg production and worm lengths were determined in golden Syrian hamsters given between five and 200 Opisthorchis viverrini metacercariae. Animals given five, 10 or 20 metacercariae showed similar worm recovery rates of 38%, 36% and 37%, respectively, whereas animals given 50, 100 or 200 metacercariae gave recoveries of 49%, 65% and 54%, respectively. The distribution of worms between right, left and middle liver lobes was similar for animals with between one and 43 worms but different for animals with between 64 and 154 worms. A curvilinear relationship between eggs found per gram of faeces per worm (epg/worm) and eggs/worm/24 hours and worm burden was observed at 60 days post-infection, with worm egg output decreasing as worm burden increased. Regression analysis of the logarithmically transformed data gave regression coefficients of r = 0.62 for log 10 epg/worm v. worm burden and r = 0.71 for log 10 eggs/worm/24 hours v. worm burden. When the same analyses were performed substituting worm density (worms/gram liver tissue) for worm burden, little or no difference was seen in the correlations obtained. A similar relationship was also observed between worm length and worm burden with mean worm length appearing to decrease with increase in worm burden. These results clearly show that worm crowding in the hamster host can have a profound effect on worm egg output and growth. The possible mechanisms underlying these phenomena are discussed and their potential relevance in human opisthorchiasis considered.

Potentiation by the human liver fluke, Opisthorchis viverrini, of the carcinogenic action of N-nitrosodimethylamine upon the biliary epithelium of the hamster

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Acquired resistance to Opisthorchis viverrini in the hamster

Two groups of ten hamsters received a primary challenge of five Opisthorchis viverrini metacercariae intragastrically (Groups I and III) and a third group was left untreated (Group II). 90 days after the primary challenge Groups I and II were given a further 50 metacercariae. Animals were killed 35 days after the secondary challenge and worm burdens and faecal egg counts evaluated. Compared with Group II animals, Group I showed a 24.88% reduction in mean liver worm burden, a difference which was significant at a level of P less than 0.01 Differences for faecal egg output/worm between Groups I and II were not significant. This is the first effective demonstration of a degree of acquired resistance to O. viverrini and the possible relevance of these findings to the disease in man is discussed.

Liver-fluke infection as an aetiological factor in bile-duct carcinoma of man

This paper reviews, with particular reference to Opisthorchis viverrini, the evidence that opisthorchiasis and clonorchiasis are aetiological factors in the causation of human bile-duct cancer, especially cholangiocarcinoma, and considers the other aetiological factors which may be operating. The epidemiology, pathology in man and experimental animals, and histogenesis of cholangiocarcinoma associated wtih liver-fluke infection are also considered.

The in vitro effects of serum on the adults, metacercariae, and eggs of Opisthorchis viverrini

Adult and juvenile Opisthorchis viverrini liver-flukes incubated in hamster chronic infection serum (CIS) developed tegumental precipitates which enclosed the entire parasite. Adult worms appeared dead by 48 hours in CIS and juvenile worms by 18 hours. No such reactions were observed in normal hamster serum (NHS). Heat inactivation of CIS at 56 degrees C abolished the precipitin reactivity against both adult and juvenile parasites though reactivity was regained upon addition of NHS or guinea-pig serum. Reactivity was also abolished by heat inactivating CIS at 60 degrees C but reactivity was not regained upon addition of NHS or guinea-pig serum. Coarse granular precipitates and blebs were observed around eggs in CIS and this activity was abolished by heat inactivating serum at 60 degrees C but not 56 degrees C. Aging of adult parasites in vitro for nine or 27 days before testing against CIS did not affect the development of tegumental precipitates although freeze-thaw killing of adult parasites before testing against CIS resulted in a marked reduction in the extent of the tegumental precipitate reaction. These results show that serum from O. viverrini-infected hamsters contains a component(s), possibly a specific immunoglobulin(s) capable of reacting with adult, juvenile and egg state parasitic antigens. These findings are discussed in relation to immunopathological processes that might be operating in the liver of the infected host.