DAPI 01 ector Labs, USA), and stained parasites were visualized using Zeiss Axioimager fluorescence microscope and the images were processed using Axio Vision software

Thin blood smears of parasite cultures were fixed with chilled methanol for 2 min. After air drying, washing with PBS and permeabilization was done with 0.05 % saponin in 3% BSA/PBS for 15 min, followed by blocking with 3% BSA made in PBS for Ih. Subsequent incubations with primary antibodies were performed for 2h at room temperature or at 4°C overnight. The smears were washed 3x5 times with PBS. The slides were then incubated with appropriate secondary antibodies (labeled either with fluorescein isothiocyanate (FITC) or Texas Red) for 1 hour at I room temperature. The slides were washed again with PBS and air dried in the dark. Smears were mounted in glycerol containing mounting media that contained

resh complete medium was added and the plates were transferred to 37°C for further incubation. The percentage infection was monitored at appropriate time intervals post-infection by staining the cells with Syto Green 11 nucleic acid dye and the parasite nuclei were visualized by fluorescence microscopy

Human THP-1 macrophages were plated at a density of 2X105 cells per well in a 24 well plate and appropriate treatments were given. The stationary phase L.major promastigotes were opsonized with 1% human AB serum in PBS for 5 min at 37°C following which one wash was given with phenol-red free RPMI-1640 medium. The L.major promastigotes were added to the macrophage culture at a macrophage: parasite ratio of 1:10 or 1:50 and incubated for 6 hat 37°C following which the unbound parasites were removed by giving 3 washes with warm RPMI-1640 medium

The kinetics of intoxication by different restrictocin containing chimeric toxins was investigated by assaying the cytotoxic activity at various time points. HUTI02, K562 and A431 cell lines were seeded at a density of IX104 cells per well in 200 J.ll medium in a similar manner as described in cytotoxicity assay. The various concentrations of chimeric toxins were added and the cells were incubated at 37 °C in the presence of 5% C02 for different time points. At the end of each incubation period cells were pulsed with eH] leucine and the protein synthesis was measured as described above. The results were expressed as percentage of control where no toxin was added to the cells.

The RIA for alpha hCG was similar to that used to estimate ~hCG. A monoclonal antibody specific to alpha hCG ( Gupta et al. , 1985 was used for the assay. The standard used was total hCG.

added and the sample vortexed thoroughly. The sample was then centrifuged for 10 minutes at 1000 x g. The supernate was carefully decanted, the rims of the tube wiped to absorb all residual supernate, and the precipitate counted on a gamma counter set for the detection of 125I. A standard curve was plotted with each assay by using different concentrations of purified hCG, starting from 0 miU 1 ml. The percent binding of the sample was estimated as a fraction of the zero standard and the hCG activity of the sample calculated from the standard curve of the known concentrations. The other RIA procedure used has been described previously by Salahuddin et al., ( 1976 ) . This procedure employed a monoclonal antibody shown to be specific to phcG (Gupta et al., 1982 ). The use of this antibody made this assay much more sensitive compared to the commercial assay described above.

J3hCG was estimated using either a commercial RIA kit ( Micromedic ~hCG RIA kit, ICN Biomedicals, Inc., USA ) or by the procedure developed at Nil, the basic principle of estimation being the same in both assays, i.e., competitive inhibition. The Micromedic kit was used as detailed by the manufacturer. Briefly, 200 ul of the sample was incubated with 100 ul of the given antiserum solution for 30 minutes at room temperature. 100 ul of the tracer 125r hCG solution was then added and incubation continued for another 3 0 minutes. Subsequently, 1. 0 ml of the precipitating solution containing anti -rabbit serum with PEG was

Quantitative determination of alpha hCG or J3hCG was performed by RIA using subunit specific antisera.

ultrapureHNO3andtissuesamplesweredissolvedin70%HNO3;microwavedfor5minat90W,180W,270Wand360W,untiltotaldigestionhadoccurredandthendilutedwithMilli-Qgradewater(Millipore,Acton,Massachusetts,U.S.A)

Totalsodium,potassiumandcalciumconcentrationsweredeterminedwithatomicabsorptionspectrophotometry.Tothispurpose,plasmasamplesweredilutedwith1%

Plasmaosmolalitywasmeasuredin10pisampleswithavaporpressure osmometer(Wescor,5500,Utah,U.S.A)andexpressedasmmol/kg

Forclinicalanalysis,thecontrolandexperimentalfishesweregentlyandrapidly anaesthetizedusingMS222(ethyl-m-aminobenzoatemethanesulphonate)atthedoseof60mgl'1.Thefisheswereimmobilizedwithin1minofapplication.Bloodwascollected fromthecaudalarteryusing1mlsyringefilledwith24Gneedleandinsomefishesbycaudalpedunclecut.Heparinwasusedastheanticoagulant.Immediatelyaftercollection,bloodwascentrifugedfor5minat3000rpmandtheplasmawasseparatedoutandeither usedforanalysisimmediatelyorstoredat20°Cforanalysislater.Samplingprocedureofnetting,anesthesiaandplasmastoringwascompletedwithin10mintoavoidinfluenceofnettingcombinedwithanesthesiaonthebasalcortisollevels(Tancketal.,2000).

epoxy resins used for infiltration and embedding are not miscible with water. This was carried out by sequentially incubating the agar blocks in 25% methanol for 5 min, 50% methanol for 7 min, 70% methanol for 10 min, 95% methanol for 20 min and finally 100% methanol for 30 min followed by two more changes of methanol for 30 min each. The blocks were then incubated with transitional solvent propylene oxide for 30 min with one change at 15 min. Epoxy resin used for infiltration penetrates the cell and fills the spaces in between providing a hard medium that can withstand the cutting and electron beams. The blocks were first incubated for 30 min with a mixture of propylene oxide and resin in a ratio of 2:1. This was followed by incubation for 60 min with propylene oxide and resin in a 1:1 ratio. Finally, the blocks were put in pure resin and kept overnight at RT under shaking conditions. The following day, the agar blocks were placed in a bean capsule and overlayed with pure resin and incubated at 55°C to allow it to harden. Sectioning and Viewing: This was carried out at the Advanced Instrumentation Research Facility at Jawaharlal Nehru University

Sample Processing: Leishmania donovani cultures to be viewed under transmission electron microscope were pelleted at 1258 x g for 5min at RT. The pellet obtained were washed with PBS (0.22p. Filtered) and then resuspended in EM Fixative ( 4% Paraformaldehyde, 25% Glutaraldehyde, 0.1M Sodium Cacodylate) which had also been passed through a 0.22 p.m filter to remove any particulate matter that may interfere later with imaging. The cells were incubated in the fixative for 4-5 hours at RT followed by overnight incubation at 4°C. Subsequently the pellets were washed with sodium cacodylate buffer (0.1M sodium cacodylate, pH 7.3). The pellet was then embedded in 3%agar to prevent loss during subsequent washings. For this, agar was added to the pellet while vortexing so that the cells and agar mix well, then the agar was allowed to set. The MCT with the agar block was then cut to extract the block which itself was cut into smaller pieces to allow the solutions that will be added later to percolate well into the agar block. Post fixation was carried out to increase contrast and stability of fine structure, by incubating with 1% osmium tetraoxide for 2hr at RT. The blocks were then washed thoroughly with distilled water. Sample dehydration has to be carried out because the

The DNA sequencing was carried out at the DBT sequencing facility, Department of Biochemistry, Delhi University, South Campus, New Delhi using the di-deoxy method (Sanger et al., 1977)