Our rat monoclonal antibodies are obtained in the form of hybridoma supernatants and these contain sodium azide (0.1% w/v) as a preservative. They can be stored at 4^oC where they will remain active for many years. They can be frozen but repeated freeze/thaw cycles should be avoided.

The antibodies are used as dilutions of between 10-fold and 100-fold in PBS (phosphate-buffered saline) with a blocking protein such as milk protein or BSA. All secondary detection antibodies should also be diluted appropriately in this buffer

Each stage of antibody incubation should be carried out for at least 1 hour. Incubations are mostly done at RT but O/N incubations can be done at 4^oC.

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Using rat monoclonal antibodies in

immunolabelling techniques:

        Immunofluorescence labelling for light microscopy

        Immunogold labelling for electron microscopy

immunochemical assays:

        Nitrocellulose-based assays (IDAs)

Immunofluorescence

Overview of antibody immunolabelling method

1. Block non-specific binding sites of prepared cells or a section of plant material adhered to a glass slide by incubation with 3% (w/v) milk protein in phosphate-buffered saline (MP/PBS) for at least 30 min.

2. Incubate with rat monoclonal antibody diluted in MP/PBS for at least 1 hr at RT or overnight at 4^oC. A five-fold dilution of a hybridoma supernatant is a good starting point for the primary antibody.

3. Wash with three changes of PBS with at least 5 min for each change.

4. Incubate with a secondary antibody diluted in the region of 100-fold in MP/PBS for 1 hr at RT.  We use anti-rat-IgG (whole molecule) linked to FITC (Sigma)

5. Wash with three changes of PBS with at least 5 min for each change.

6. Mount slides using an antifade reagent and examine. We use Citifluor glycerol-based antifade for sections.

Immunogold

Overview of antibody immunolabelling method

1. Block to prevent non-specific binding by floating the EM grid section side down on a droplet (at least 20 ml) of 3% (w/v) bovine serum albumin in phosphate-buffered saline (BSA/PBS) on Parafilm for 30 min.

2. Transfer grid to a droplet of primary antibody diluted in BSA/PBS. Monoclonal antibodies should be diluted between 5-fold and 100-fold.

3. Wash grids by incubation in a minimum of three changes of PBS.

4. Transfer grids to secondary antibody diluted 1 in 20 with BSA/PBS. We use anti-rat IgG coupled to 10 nm gold (Sigma).

5. Wash as in step 3 and then extensively in distilled water.

6. Allow the grid to dry and then examine in an electron microscope.

IDAs

Overview of method for immuno-dot assays/tissue printing

1. Mark out assay sites on an appropriately-sized piece of nitrocellulose membrane (Schleicher & Schuell) by carefully ruled lines with a soft pencil. We use 5 mm x 5 mm squares. 1 μl aliquots of test compounds dissolved in water or appropriate buffer are applied to nitrocellulose and left to dry for 1 hr. It is useful to use a dilution series. Alternatively make a tissue print of plant material.

2. Incubate sheet in 3% (w/v) milk protein in phosphate-buffered saline (MP/PBS) for 1 hr to block all binding sites.

3. Incubate in primary antibody for 1.5 hr. Rat hybridoma supernatants are diluted at least 10-fold in MP/PBS.

4. Wash extensively in PBS. In most cases we find that tap water can be a suitable alternative to PBS.

5. Incubate in secondary antibody (e.g. anti-rat IgG(whole molecule) coupled to horseradish peroxidase (HRP), Sigma) diluted in the region of 1000-fold in MP/PBS for 1.5 hr.

6. Wash extensively in PBS. See step 4.

7. Determine antibody binding to the nitrocellulose by the incubation in enzyme marker substrate prepared immediately before use (e.g. HRP susbstrate: 25 ml de-ionized water, 5 ml methanol containing 10 mg/ml 4-chloro-1-naphthol, 30 μl 6% (v/v) hydrogen peroxide). prepared immediately before use) and allow to develop.

8. Stop reaction when dark dots have appeared at antigen sites, by washing extensively in tap water.

ELISAs

Overview of method for antibody-capture ELISA

1. Adjust a sample that is to be used as an immobilised antigen to a concentration of c. 50 μg/ml in 50 mM sodium carbonate, pH 9.6.

2. Add 100 μl of antigen to appropriate wells of a microtitre plate and incubate overnight at 4^oC (or 2 hr at RT). It is useful to have wells without antigen to determine signal with no antibody binding.

3. Remove solutions containing antigen.

4. Block all binding sites on the plate with 200 μl/well 3% (w/v) bovine serum albumin in phosphate-buffered saline (BSA/PBS) for 2 hr at RT or O/N at 4^oC.

5. Wash plates with PBS. This is most readily done by the repeated submerging of plates in trays full of PBS, shaking and then forcibly throwing the PBS out (into a sink). This is repeated at least fifteen times. In our hands, tap water can often be a suitable alternative washing medium.

6. Add 100 μl/well of the primary antibody at appropriate dilution in BSA/PBS for at least 1.5 hr. As a guide, rat hybridoma supernatants are diluted 10-fold followed by 5- or 10-fold dilutions.

7. Wash plates fifteen times as in step 5.

8. Add 100 μl/well of secondary antibody (e.g. anti-rat IgG(whole molecule) coupled to horseradish peroxidase (HRP), Sigma) diluted in the region of 1000-fold in BSA/PBS.

9. Incubate for at least 1.5 hr.

10. Wash plates fifteen times as in step 5.

11. Determine antibody binding to the plates by the addition 150 μl/well of HRP substrate prepared immediately before use (18 ml de-ionized water, 2 ml 1 M sodium acetate buffer pH 6.0, 200 μl tetramethylbenzidene, 20 μl 6% (v/v) hydrogen peroxide). 

12. Colour development is stopped by the addition of 35 μl/well of 2 N sulphuric acid.

13. Absorbances are determined at 450 nm in a microplate reader.

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Overview of method for competitive-inhibition ELISA

1. Microtitre plates are coated with antigen (the immobilised antigen) and blocked with BSA/PBS.

2. Determine a primary antibody dilution (x) that gives 90% of maximal binding with this antigen in antibody capture ELISA (see above & Fig. A).

3. Add 50 μl/well of a serially-diluted soluble antigen or hapten in PBS to appropriate wells of a microtitre plate. As a guide, start at 2 mg/ml and prepare 10-fold dilutions.

4. Add to each well containing antigen from step 3, 50 μl/well of primary antibody in BSA/PBS at a concentration of 2x. This will give a final concentration of antigen of 1 mg/ml (with 10-fold dilutions) and an antibody concentration of x. Agitate the microtitre plate gently to ensure mixing.

5. Incubate for at least 1.5 hr.

6. Wash plates with PBS. This is most readily done by the repeated submerging of plates in trays full of PBS, shaking and then forcibly throwing the PBS out (into a sink). This is repeated at least fifteen times. In our hands, tap water can often be a suitable alternative washing medium.

7. Add 100 μl/well of secondary antibody (e.g. anti-rat IgG(whole molecule) coupled to horseradish peroxidase (HRP), Sigma) diluted in the region of 1000-fold in BSA/PBS.

8. Incubate for at least 1.5 hr.

9. Carry out steps 8 to 13 in antibody-capture ELISA protocol above.

10. Determine the concentration of antigen required to inhibit antibody binding by 50% as shown in Fig. B. This is known as the IC50. Comparing the IC50 of a range of antigens gives a good indication of extent of their recognition by a particular antibody.