Rabbit IgG Isotype Control Antibody (Rabbit mAb) [D24D4]

Application: Reactivity:

Usage Information

Dilution
IP1:50-1:200 IHC1:100 IF1:100 FCM1:100 CHIP1:50-1:100

Application
IP, IHC, IF, FCM, ChIP

Reactivity

Source
Rabbit Monoclonal Antibody

Storage Buffer
PBS, pH 7.2+50% Glycerol+0.05% BSA+0.01% NaN3

Storage (from the date of receipt)
'-20°C (avoid freeze-thaw cycles), 2 years

Positive Control	HeLa cells; A549 cells; Hep G2 cells
Negative Control	Human colon carcinoma

Experimental Methods

IF
Experimental Protocol: Sample Preparation 1. Adherent Cells: Place a clean, sterile coverslip in a culture dish. Once the cells grow to near confluence as a monolayer, remove the coverslip for further use. 2. Suspension Cells: Seed the cells onto a clean, sterile slide coated with poly-L-lysine. 3. Frozen Sections: Allow the slide to thaw at room temperature. Wash it with pure water or PBS for 2 times, 3 minutes each time. 4. Paraffin Sections: Deparaffinization and rehydration. Wash the slide with pure water or PBS for 3 times, 3 minutes each time. Then perform antigen retrieval. Fixation 1. Fix the cell coverslips/spots or tissue sections at room temperature using a fixative such as 4% paraformaldehyde (4% PFA) for 10-15 minutes. 2. Wash the sample with PBS for 3 times, 3 minutes each time. Permeabilization 1.Add a detergent such as 0.1–0.3% Triton X-100 to the sample and incubate at room temperature for 10–20 minutes. (Note: This step is only required for intracellular antigens. For antigens expressed on the cell membrane, this step is unnecessary.) Wash the sample with PBS for 3 times, 3 minutes each time. Blocking Add blocking solution and incubate at room temperature for at least 1 hour. (Common blocking solutions include: serum from the same source as the secondary antibody, BSA, or goat serum.) Note: Ensure the sample remains moist during and after the blocking step to prevent drying, which can lead to high background. Immunofluorescence Staining (Day 1) 1. Remove the blocking solution and add the diluted primary antibody. 2. Incubate the sample in a humidified chamber at 4°C overnight. Immunofluorescence Staining (Day 2) 1. Remove the primary antibody and wash with PBST for 3 times, 5 minutes each time. 2. Add the diluted fluorescent secondary antibody and incubate in the dark at 4°C for 1–2 hours. 3. Remove the secondary antibody and wash with PBST for 3 times, 5 minutes each time. 4. Add diluted DAPI and incubate at room temperature in the dark for 5–10 minutes. 5. Wash with PBST for 3 times, 5 minutes each time. Mounting 1. Mount the sample with an anti-fade mounting medium. 2. Allow the slide to dry at room temperature overnight in the dark. 3. Store the slide in a slide storage box at 4°C, protected from light.

IF

Experimental Protocol:

Sample Preparation

1. Adherent Cells: Place a clean, sterile coverslip in a culture dish. Once the cells grow to near confluence as a monolayer, remove the coverslip for further use.

2. Suspension Cells: Seed the cells onto a clean, sterile slide coated with poly-L-lysine.

3. Frozen Sections: Allow the slide to thaw at room temperature. Wash it with pure water or PBS for 2 times, 3 minutes each time.

4. Paraffin Sections: Deparaffinization and rehydration. Wash the slide with pure water or PBS for 3 times, 3 minutes each time. Then perform antigen retrieval.

Fixation

1. Fix the cell coverslips/spots or tissue sections at room temperature using a fixative such as 4% paraformaldehyde (4% PFA) for 10-15 minutes.

2. Wash the sample with PBS for 3 times, 3 minutes each time.

Permeabilization

1.Add a detergent such as 0.1–0.3% Triton X-100 to the sample and incubate at room temperature for 10–20 minutes.

(Note: This step is only required for intracellular antigens. For antigens expressed on the cell membrane, this step is unnecessary.)

Wash the sample with PBS for 3 times, 3 minutes each time.

Blocking

Add blocking solution and incubate at room temperature for at least 1 hour. (Common blocking solutions include: serum from the same source as the secondary antibody, BSA, or goat serum.)

Note: Ensure the sample remains moist during and after the blocking step to prevent drying, which can lead to high background.

Immunofluorescence Staining (Day 1)

1. Remove the blocking solution and add the diluted primary antibody.

2. Incubate the sample in a humidified chamber at 4°C overnight.

Immunofluorescence Staining (Day 2)

1. Remove the primary antibody and wash with PBST for 3 times, 5 minutes each time.

2. Add the diluted fluorescent secondary antibody and incubate in the dark at 4°C for 1–2 hours.

3. Remove the secondary antibody and wash with PBST for 3 times, 5 minutes each time.

4. Add diluted DAPI and incubate at room temperature in the dark for 5–10 minutes.

5. Wash with PBST for 3 times, 5 minutes each time.

Mounting

1. Mount the sample with an anti-fade mounting medium.

2. Allow the slide to dry at room temperature overnight in the dark.

3. Store the slide in a slide storage box at 4°C, protected from light.

IHC
Experimental Protocol： Deparaffinization/Rehydration 1. Deparaffinize/hydrate sections: 2. Incubate sections in three washes of xylene for 5 min each. 3. Incubate sections in two washes of 100% ethanol for 10 min each. 4. Incubate sections in two washes of 95% ethanol for 10 min each. 5. Wash sections two times in dH2O for 5 min each. 6.Antigen retrieval: For Citrate: Heat slides in a microwave submersed in 1X citrate unmasking solution until boiling is initiated; continue with 10 min at a sub-boiling temperature (95°-98°C). Cool slides on bench top for 30 min. Staining 1. Wash sections in dH2O three times for 5 min each. 2. Incubate sections in 3% hydrogen peroxide for 10 min. 3. Wash sections in dH2O two times for 5 min each. 4. Wash sections in wash buffer for 5 min. 5. Block each section with 100–400 µl of blocking solution for 1 hr at room temperature. 6. Remove blocking solution and add 100–400 µl primary antibody diluent in to each section. Incubate overnight at 4°C. 7. Remove antibody solution and wash sections with wash buffer three times for 5 min each. 8. Cover section with 1–3 drops HRPas needed. Incubate in a humidified chamber for 30 min at room temperature. 9. Wash sections three times with wash buffer for 5 min each. 10. Add DAB Chromogen Concentrate to DAB Diluent and mix well before use. 11. Apply 100–400 µl DAB to each section and monitor closely. 1–10 min generally provides an acceptable staining intensity. 12. Immerse slides in dH2O. 13. If desired, counterstain sections with hematoxylin. 14. Wash sections in dH2O two times for 5 min each. 15. Dehydrate sections: Incubate sections in 95% ethanol two times for 10 sec each; Repeat in 100% ethanol, incubating sections two times for 10 sec each; Repeat in xylene, incubating sections two times for 10 sec each. 16. Mount sections with coverslips and mounting medium.

IHC

Experimental Protocol：

Deparaffinization/Rehydration

1. Deparaffinize/hydrate sections:

2. Incubate sections in three washes of xylene for 5 min each.

3. Incubate sections in two washes of 100% ethanol for 10 min each.

4. Incubate sections in two washes of 95% ethanol for 10 min each.

5. Wash sections two times in dH2O for 5 min each.

6.Antigen retrieval: For Citrate: Heat slides in a microwave submersed in 1X citrate unmasking solution until boiling is initiated; continue with 10 min at a sub-boiling temperature (95°-98°C). Cool slides on bench top for 30 min.

Staining

1. Wash sections in dH2O three times for 5 min each.

2. Incubate sections in 3% hydrogen peroxide for 10 min.

3. Wash sections in dH2O two times for 5 min each.

4. Wash sections in wash buffer for 5 min.

5. Block each section with 100–400 µl of blocking solution for 1 hr at room temperature.

6. Remove blocking solution and add 100–400 µl primary antibody diluent in to each section. Incubate overnight at 4°C.

7. Remove antibody solution and wash sections with wash buffer three times for 5 min each.

8. Cover section with 1–3 drops HRPas needed. Incubate in a humidified chamber for 30 min at room temperature.

9. Wash sections three times with wash buffer for 5 min each.

10. Add DAB Chromogen Concentrate to DAB Diluent and mix well before use.

11. Apply 100–400 µl DAB to each section and monitor closely. 1–10 min generally provides an acceptable staining intensity.

12. Immerse slides in dH2O.

13. If desired, counterstain sections with hematoxylin.

14. Wash sections in dH2O two times for 5 min each.

15. Dehydrate sections: Incubate sections in 95% ethanol two times for 10 sec each; Repeat in 100% ethanol, incubating sections two times for 10 sec each; Repeat in xylene, incubating sections two times for 10 sec each.

16. Mount sections with coverslips and mounting medium.

IP
Experimental Procedure: Reagents and Preparation 1. Basic buffers: 1× PBS or 1× TBS (pre-chilled on ice); 1× cell lysis buffer (add 1 mM PMSF protease inhibitor immediately before use; add phosphatase inhibitors for phosphoproteins). 2. Capture medium: Protein A/G magnetic beads or agarose beads (Sepharose beads). 3. Controls: Use an isotype control IgG matching the host species and IgG subclass of the primary antibody, at the same concentration. It is recommended to reserve a portion of the cell lysate that has not been subjected to immunoprecipitation as the Input control; if necessary, a beads-only control (beads added without antibody) may also be included. 4. Loading and elution reagents: 3× or 4× SDS sample loading buffer (containing DTT/reducing agent); if non-denaturing elution is to be performed, prepare the corresponding elution buffer and neutralization buffer separately; for denaturing elution, 1× PBS is typically used to dilute the 3× or 4× SDS sample loading buffer to 1×. Cell Lysis and Sample Preparation (Native Protein Extraction) 1. Cell harvesting: Discard the culture medium and wash the cells once with ice-cold 1× PBS. 2. Cell lysis: Add 0.5–1 mL of ice-cold 1× cell lysis buffer to a 10-cm culture dish and incubate on ice for 5–10 minutes. 3. Lysate collection and clarification: Scrape the cells and transfer the lysate to a microcentrifuge tube. Some adherent cells may require detachment using digestive enzymes or mechanical methods. Centrifuge at 14,000 rpm at 4°C for 5–15 min. Collect the supernatant as the clarified cell lysate. It is recommended to determine the protein concentration. Pre-clearing and Immunoprecipitation Reaction 1. Pre-clearing of the lysate (recommended): Take an appropriate amount of beads (magnetic beads or agarose beads) and pre-wash 2–3 times with cell lysis buffer or 1× TBS/PBS. After pre-washing, it is recommended to remove the wash buffer as completely as possible before adding subsequent reagents, to avoid extra dilution of the sample. For lysis systems containing detergents or specific salt concentrations, prefer pre-washing with a buffer identical or compatible with the lysis buffer to minimize buffer-system mismatches. 2. Pre-clearing treatment: Mix the cell lysate with the pre-washed beads and incubate with rotation at room temperature for 30–60 min, or at 4°C with rotation for 1–2 h. When using agarose beads, pellet the beads by centrifugation after incubation and collect the supernatant. When using magnetic beads, separate the beads using a magnetic stand after incubation and collect the supernatant. This step removes proteins that bind non-specifically to the beads. For unstable proteins, phosphoproteins, or protein complexes, incubation at 4°C is preferred to minimize protein degradation, dephosphorylation, or complex dissociation. Beads used for pre-clearing should generally not be pre-coupled with a specific antibody, to avoid loss of the target antigen. 3. Formation of the “bead–antibody–antigen” immunocomplex Either of the following two approaches may be used: 3.1 Pre-form the antibody–antigen complex, then add the beads: Add an appropriate amount of primary antibody to the pre-cleared supernatant obtained in step 2, and set up an isotype control IgG group in parallel. Incubate with rotation at 4°C overnight (recommended), or at room temperature with rotation for 2 h, to allow formation of the antibody–antigen complex. In parallel, take an appropriate amount of beads and pre-wash them as described in step 1 of this section. Add the antibody–antigen complex to the pre-washed magnetic or agarose beads and incubate with rotation at room temperature for 30 min–1 h, or at 4°C with rotation for 1–2 h, to allow the antibody–antigen complex to bind efficiently to the beads. 3.2 Pre-form the bead–antibody complex, then add the cell lysate: Dilute the primary antibody in cell lysis buffer at the dilution ratio recommended in the antibody instruction manual to prepare the antibody working solution. Add an appropriate amount of pre-washed magnetic beads to the antibody working solution and incubate with rotation at room temperature for 15 min, or at 4°C with rotation for 1 h, to form the bead–antibody complex. Recover the beads by magnetic separation or centrifugation, discard the supernatant, and pre-wash the beads 2–3 times with 1× TBS. Then add the cell lysate and incubate with rotation at 4°C overnight (recommended), or at room temperature with rotation for 2 h. Washing of the Precipitate and Sample Elution 1. Once immunoprecipitation is complete, separate the beads according to their type and discard the supernatant. Magnetic beads are separated using a magnetic stand. For agarose beads, low-speed centrifugation (500–1000 rpm) appropriate for the bead specifications should be used, to avoid bead compaction or damage caused by high-speed centrifugation. 2. Washing the beads: Gently wash the beads 3–5 times with ice-cold 1× cell lysis buffer or 1× TBS/TBST. Keep the temperature low throughout the washes. After each addition of wash buffer, mix gently to fully resuspend the beads; then separate the beads using a magnetic stand or appropriate centrifugation, depending on the bead type, and remove the wash buffer thoroughly to minimize unbound and non-specifically bound components. During each wash, remove as much supernatant as possible while avoiding aspiration of the beads. After the final wash, remove residual wash buffer as completely as possible to prevent dilution of the eluate or interference with downstream analyses. Keep the samples on ice after each wash. 3. Sample elution (choose one of the following): 3.1 Denaturing direct elution (most commonly used): Add SDS sample loading buffer to the bead pellet to a final concentration of 1×. If 3× or 4× SDS sample loading buffer is used, it must first be diluted to 1×. Mix well and heat at 95–100°C for 5 minutes. Separate the beads and collect the supernatant for subsequent electrophoresis. 3.2 Chemical / non-denaturing elution (preserves protein activity): After the final wash, separate the beads using a magnetic stand or low-speed centrifugation, depending on the bead type, and remove residual wash buffer as completely as possible to prevent dilution of the eluate. Add an appropriate amount of acidic elution buffer / high-salt elution buffer to the beads and resuspend them thoroughly. Mix gently and incubate briefly at room temperature to allow the immunocomplex to dissociate from the beads. Separate the beads with a magnetic stand or low-speed centrifugation, and transfer the eluate to a collection tube pre-filled with an appropriate amount of neutralization buffer; adjust the pH if necessary. To improve recovery, elution may be repeated and the eluates pooled. The composition and volume of the elution buffer and neutralization buffer should be determined according to the instructions for the beads and kit used. 3.3 Post-elution sample handling For protein activity assays, native protein complex analysis, or other non-denaturing analyses: do not add SDS sample loading buffer; keep the sample on ice and proceed to the subsequent experiment as quickly as possible. For SDS-PAGE or Western blot: add SDS sample loading buffer to the neutralized or desalted eluate to a final concentration of 1×, and then process the sample according to the subsequent electrophoresis requirements. Select appropriate storage conditions according to the stability of the target protein and the requirements of downstream experiments, and avoid repeated freeze–thaw cycles. Downstream Analysis Western blot analysis: Take the supernatant and perform SDS-PAGE electrophoresis followed by membrane transfer. It is recommended to use light- and heavy-chain-specific or conformation-specific secondary antibodies to avoid interference of the immunoglobulin heavy/light chain bands (50 kDa / 25 kDa) with detection of the target protein. It is recommended to include Input, isotype control IgG-IP, and target antibody-IP samples on the same Western blot; if necessary, a beads-only control may also be added to evaluate immunoprecipitation efficiency and non-specific binding. Kinase activity assay (if applicable): skip the denaturation step, wash the beads with kinase buffer, then add substrate and ATP directly to perform the kinase reaction. Note: All lysis and immunoprecipitation procedures should be performed at 4°C or on ice to preserve the native conformation of proteins as much as possible and prevent their degradation.

IP

Experimental Procedure:

Reagents and Preparation

1. Basic buffers: 1× PBS or 1× TBS (pre-chilled on ice); 1× cell lysis buffer (add 1 mM PMSF protease inhibitor immediately before use; add phosphatase inhibitors for phosphoproteins).

2. Capture medium: Protein A/G magnetic beads or agarose beads (Sepharose beads).

3. Controls: Use an isotype control IgG matching the host species and IgG subclass of the primary antibody, at the same concentration. It is recommended to reserve a portion of the cell lysate that has not been subjected to immunoprecipitation as the Input control; if necessary, a beads-only control (beads added without antibody) may also be included.

4. Loading and elution reagents: 3× or 4× SDS sample loading buffer (containing DTT/reducing agent); if non-denaturing elution is to be performed, prepare the corresponding elution buffer and neutralization buffer separately; for denaturing elution, 1× PBS is typically used to dilute the 3× or 4× SDS sample loading buffer to 1×.

Cell Lysis and Sample Preparation (Native Protein Extraction)

1. Cell harvesting: Discard the culture medium and wash the cells once with ice-cold 1× PBS.

2. Cell lysis: Add 0.5–1 mL of ice-cold 1× cell lysis buffer to a 10-cm culture dish and incubate on ice for 5–10 minutes.

3. Lysate collection and clarification: Scrape the cells and transfer the lysate to a microcentrifuge tube. Some adherent cells may require detachment using digestive enzymes or mechanical methods. Centrifuge at 14,000 rpm at 4°C for 5–15 min. Collect the supernatant as the clarified cell lysate. It is recommended to determine the protein concentration.

Pre-clearing and Immunoprecipitation Reaction

1. Pre-clearing of the lysate (recommended): Take an appropriate amount of beads (magnetic beads or agarose beads) and pre-wash 2–3 times with cell lysis buffer or 1× TBS/PBS. After pre-washing, it is recommended to remove the wash buffer as completely as possible before adding subsequent reagents, to avoid extra dilution of the sample. For lysis systems containing detergents or specific salt concentrations, prefer pre-washing with a buffer identical or compatible with the lysis buffer to minimize buffer-system mismatches.

2. Pre-clearing treatment: Mix the cell lysate with the pre-washed beads and incubate with rotation at room temperature for 30–60 min, or at 4°C with rotation for 1–2 h.

When using agarose beads, pellet the beads by centrifugation after incubation and collect the supernatant.

When using magnetic beads, separate the beads using a magnetic stand after incubation and collect the supernatant.

This step removes proteins that bind non-specifically to the beads. For unstable proteins, phosphoproteins, or protein complexes, incubation at 4°C is preferred to minimize protein degradation, dephosphorylation, or complex dissociation. Beads used for pre-clearing should generally not be pre-coupled with a specific antibody, to avoid loss of the target antigen.

3. Formation of the “bead–antibody–antigen” immunocomplex

Either of the following two approaches may be used:

3.1 Pre-form the antibody–antigen complex, then add the beads: Add an appropriate amount of primary antibody to the pre-cleared supernatant obtained in step 2, and set up an isotype control IgG group in parallel. Incubate with rotation at 4°C overnight (recommended), or at room temperature with rotation for 2 h, to allow formation of the antibody–antigen complex.

In parallel, take an appropriate amount of beads and pre-wash them as described in step 1 of this section. Add the antibody–antigen complex to the pre-washed magnetic or agarose beads and incubate with rotation at room temperature for 30 min–1 h, or at 4°C with rotation for 1–2 h, to allow the antibody–antigen complex to bind efficiently to the beads.

3.2 Pre-form the bead–antibody complex, then add the cell lysate: Dilute the primary antibody in cell lysis buffer at the dilution ratio recommended in the antibody instruction manual to prepare the antibody working solution. Add an appropriate amount of pre-washed magnetic beads to the antibody working solution and incubate with rotation at room temperature for 15 min, or at 4°C with rotation for 1 h, to form the bead–antibody complex.

Recover the beads by magnetic separation or centrifugation, discard the supernatant, and pre-wash the beads 2–3 times with 1× TBS. Then add the cell lysate and incubate with rotation at 4°C overnight (recommended), or at room temperature with rotation for 2 h.

Washing of the Precipitate and Sample Elution

1. Once immunoprecipitation is complete, separate the beads according to their type and discard the supernatant.

Magnetic beads are separated using a magnetic stand.

For agarose beads, low-speed centrifugation (500–1000 rpm) appropriate for the bead specifications should be used, to avoid bead compaction or damage caused by high-speed centrifugation.

2. Washing the beads: Gently wash the beads 3–5 times with ice-cold 1× cell lysis buffer or 1× TBS/TBST. Keep the temperature low throughout the washes. After each addition of wash buffer, mix gently to fully resuspend the beads; then separate the beads using a magnetic stand or appropriate centrifugation, depending on the bead type, and remove the wash buffer thoroughly to minimize unbound and non-specifically bound components. During each wash, remove as much supernatant as possible while avoiding aspiration of the beads. After the final wash, remove residual wash buffer as completely as possible to prevent dilution of the eluate or interference with downstream analyses. Keep the samples on ice after each wash.

3. Sample elution (choose one of the following):

3.1 Denaturing direct elution (most commonly used): Add SDS sample loading buffer to the bead pellet to a final concentration of 1×. If 3× or 4× SDS sample loading buffer is used, it must first be diluted to 1×. Mix well and heat at 95–100°C for 5 minutes. Separate the beads and collect the supernatant for subsequent electrophoresis.

3.2 Chemical / non-denaturing elution (preserves protein activity): After the final wash, separate the beads using a magnetic stand or low-speed centrifugation, depending on the bead type, and remove residual wash buffer as completely as possible to prevent dilution of the eluate. Add an appropriate amount of acidic elution buffer / high-salt elution buffer to the beads and resuspend them thoroughly. Mix gently and incubate briefly at room temperature to allow the immunocomplex to dissociate from the beads. Separate the beads with a magnetic stand or low-speed centrifugation, and transfer the eluate to a collection tube pre-filled with an appropriate amount of neutralization buffer; adjust the pH if necessary. To improve recovery, elution may be repeated and the eluates pooled. The composition and volume of the elution buffer and neutralization buffer should be determined according to the instructions for the beads and kit used.

3.3 Post-elution sample handling

For protein activity assays, native protein complex analysis, or other non-denaturing analyses: do not add SDS sample loading buffer; keep the sample on ice and proceed to the subsequent experiment as quickly as possible.

For SDS-PAGE or Western blot: add SDS sample loading buffer to the neutralized or desalted eluate to a final concentration of 1×, and then process the sample according to the subsequent electrophoresis requirements.

Select appropriate storage conditions according to the stability of the target protein and the requirements of downstream experiments, and avoid repeated freeze–thaw cycles.

Downstream Analysis

Western blot analysis: Take the supernatant and perform SDS-PAGE electrophoresis followed by membrane transfer. It is recommended to use light- and heavy-chain-specific or conformation-specific secondary antibodies to avoid interference of the immunoglobulin heavy/light chain bands (50 kDa / 25 kDa) with detection of the target protein. It is recommended to include Input, isotype control IgG-IP, and target antibody-IP samples on the same Western blot; if necessary, a beads-only control may also be added to evaluate immunoprecipitation efficiency and non-specific binding. Kinase activity assay (if applicable): skip the denaturation step, wash the beads with kinase buffer, then add substrate and ATP directly to perform the kinase reaction.

Note: All lysis and immunoprecipitation procedures should be performed at 4°C or on ice to preserve the native conformation of proteins as much as possible and prevent their degradation.

Datasheet & SDS

Biological Description

Specificity
Rabbit IgG Isotype Control Antibody (Rabbit mAb) [D24D4] functions as an isotype control for rabbit IgG antibodies.

Clone
D24D4

Background
Rabbit IgG isotype control antibodies are immunoglobulin G class rabbit antibodies that possess the same constant region and Y-shaped structure as target-specific rabbit IgG, including paired heavy and light chains with an Fc region capable of engaging Fc receptors and complement, and Fab regions that lack specificity for antigens in the test system. The Fc portion retains the ability to bind Fcγ receptors, interact with Fc-binding proteins, and participate in non-antigen-driven associations with cellular lipids, carbohydrates, and extracellular matrix components, while the variable domains do not recognize the epitopes under investigation, resulting in a nonspecific binding profile equivalent to that of a typical rabbit primary antibody without contributing target-directed signal. Under experimental conditions, rabbit IgG isotype controls serve as negative controls to define background resulting from Fc receptor binding, weak protein–protein or protein–surface interactions, and fluorophore or enzyme conjugates, and are used at the same immunoglobulin class, subclass, and concentration as the test antibody to ensure equivalent avidity, Fc interactions, and labeling density. In flow cytometry, immunohistochemistry, and immunofluorescence, isotype control IgG binds Fc receptors on leukocytes and tissue-resident immune cells and engages nonspecific sites to the same extent as a typical rabbit primary antibody, allowing direct comparison of signal between isotype and test antibody channels and establishing a threshold that separates specific antigen-dependent staining from background. During chromatin immunoprecipitation, RIP, ELISA, or immunoprecipitation, normal rabbit IgG functions as a matrix-binding and chromatin-binding control that reports non-epitope-directed capture of nucleic acids and proteins on support surfaces under conditions identical to those used for the antigen-specific antibody. The constant-region structure of rabbit IgG enables recognition by anti-rabbit secondary antibodies and by protein A or protein G, allowing rabbit IgG isotype controls to integrate into detection and purification systems and report signal originating from secondary reagents, enzyme or fluorophore tags, or capture matrices. In multiparameter flow cytometry panels using directly conjugated rabbit antibodies, conjugated rabbit IgG isotype controls match fluorophore, isotype, and concentration, quantifying background from fluorochrome-related and Fc-mediated interactions and enabling gates and positivity thresholds to be set relative to this baseline. Across these applications, rabbit IgG isotype controls enhance assay robustness in samples with abundant Fc receptor–positive cells or high intrinsic autofluorescence by distinguishing true antigen-dependent signal from noise due to Fc–ligand interactions and nonspecific adsorption. In disease-oriented and translational studies reliant on antibody-based readouts, rabbit IgG isotype controls provide a reference for interpreting biomarker expression levels and distribution, ensuring that staining patterns attributed to pathology are not explained by altered Fc receptor expression or matrix composition alone.

Background

Rabbit IgG isotype control antibodies are immunoglobulin G class rabbit antibodies that possess the same constant region and Y-shaped structure as target-specific rabbit IgG, including paired heavy and light chains with an Fc region capable of engaging Fc receptors and complement, and Fab regions that lack specificity for antigens in the test system. The Fc portion retains the ability to bind Fcγ receptors, interact with Fc-binding proteins, and participate in non-antigen-driven associations with cellular lipids, carbohydrates, and extracellular matrix components, while the variable domains do not recognize the epitopes under investigation, resulting in a nonspecific binding profile equivalent to that of a typical rabbit primary antibody without contributing target-directed signal. Under experimental conditions, rabbit IgG isotype controls serve as negative controls to define background resulting from Fc receptor binding, weak protein–protein or protein–surface interactions, and fluorophore or enzyme conjugates, and are used at the same immunoglobulin class, subclass, and concentration as the test antibody to ensure equivalent avidity, Fc interactions, and labeling density. In flow cytometry, immunohistochemistry, and immunofluorescence, isotype control IgG binds Fc receptors on leukocytes and tissue-resident immune cells and engages nonspecific sites to the same extent as a typical rabbit primary antibody, allowing direct comparison of signal between isotype and test antibody channels and establishing a threshold that separates specific antigen-dependent staining from background. During chromatin immunoprecipitation, RIP, ELISA, or immunoprecipitation, normal rabbit IgG functions as a matrix-binding and chromatin-binding control that reports non-epitope-directed capture of nucleic acids and proteins on support surfaces under conditions identical to those used for the antigen-specific antibody. The constant-region structure of rabbit IgG enables recognition by anti-rabbit secondary antibodies and by protein A or protein G, allowing rabbit IgG isotype controls to integrate into detection and purification systems and report signal originating from secondary reagents, enzyme or fluorophore tags, or capture matrices. In multiparameter flow cytometry panels using directly conjugated rabbit antibodies, conjugated rabbit IgG isotype controls match fluorophore, isotype, and concentration, quantifying background from fluorochrome-related and Fc-mediated interactions and enabling gates and positivity thresholds to be set relative to this baseline. Across these applications, rabbit IgG isotype controls enhance assay robustness in samples with abundant Fc receptor–positive cells or high intrinsic autofluorescence by distinguishing true antigen-dependent signal from noise due to Fc–ligand interactions and nonspecific adsorption. In disease-oriented and translational studies reliant on antibody-based readouts, rabbit IgG isotype controls provide a reference for interpreting biomarker expression levels and distribution, ensuring that staining patterns attributed to pathology are not explained by altered Fc receptor expression or matrix composition alone.

References
https://pubmed.ncbi.nlm.nih.gov/28336958/ https://pubmed.ncbi.nlm.nih.gov/29263082/

Protein Size (kDa)	PVDF Transfer Membrane Pore Size (μm)
< 10	0.22
10-20	0.22
20-30	0.45
30-45	0.45
45-70	0.45
80-100	0.45
100-140	0.45
> 140	0.45

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Protein Size (kDa)	Separating Gel Percentage
4-40	20%
12-45	15%
10-70	12.5%
15-100	10%
25-100	8%
60-210	5%