Rabbit Serum | Normal Rabbit Serum (NRS) | Sterile Filtered | EU Origin

What is the difference between Normal Rabbit Serum (NRS) and pre-immune rabbit serum?

Normal Rabbit Serum (NRS) is collected from non-immunised rabbits with no defined antigen exposure — it contains a broad background of rabbit immunoglobulins with no specific antibody against a defined target. Pre-immune serum is collected from the same individual rabbit immediately before immunisation with a specific antigen, establishing the baseline antibody background for that animal. Pre-immune serum is used as the matched negative control in polyclonal antibody production experiments, confirming that any signal observed with the immune serum is antigen-specific. SeamlessBio NRS is suitable for standard blocking applications; pre-immune rabbit serum is available on request.

At what concentration should Normal Rabbit Serum be used for IHC and IFA blocking?

The standard working concentration for NRS blocking in IHC and IFA is 2–10% (v/v) in phosphate-buffered saline (PBS) or TBS, applied for 30–60 minutes at room temperature prior to primary antibody incubation. The optimal concentration depends on tissue type, fixation method, and secondary antibody. Higher concentrations (5–10%) are recommended for tissues with high non-specific binding potential (liver, kidney, lymph node). Always use NRS from the same species as the secondary antibody — in this case, a rabbit-derived secondary antibody system — to maximise blocking efficacy. Titration at the outset of protocol development is recommended to balance background suppression with signal preservation.

Is heat-inactivated Normal Rabbit Serum available, and when is it needed?

Yes — heat-inactivated NRS (56 °C, 30 minutes) is available on request. Heat inactivation denatures complement proteins in the serum, which is required when complement activity would interfere with the assay — for example, in complement fixation tests (CFT), cytotoxicity assays, or certain cell-based protocols where complement-mediated lysis must be excluded. For standard IHC, IFA, and ELISA blocking applications, non-heat-inactivated NRS is preferred, as the complete protein content provides more effective background suppression. Contact us with your protocol requirements to confirm the appropriate format.

Can Normal Rabbit Serum be used as a blocking reagent with rabbit-derived secondary antibodies?

Yes — this is the primary application of NRS. When using a secondary antibody raised in rabbit (e.g., rabbit anti-mouse IgG conjugated to HRP or a fluorophore), pre-blocking with 2–10% NRS saturates non-specific binding sites on the tissue or membrane surface, preventing the secondary antibody from producing background signal at sites where no primary antibody is bound. The blocking serum must come from the same species as the host of the secondary antibody. NRS is not suitable with anti-rabbit secondary antibodies (e.g., goat anti-rabbit), because the secondary antibody would bind the rabbit immunoglobulins in the blocking serum — in that case, use serum from the secondary antibody host species, such as goat or donkey serum.

What other animal sera does SeamlessBio supply for blocking and immunoassay applications?

SeamlessBio supplies a full range of normal animal sera for IHC, IFA, ELISA, and complement applications, all sterile filtered at 0.2 µm with full CoA, CoO, and SDS documentation: Normal Mouse Serum (NMS), Normal Rat Serum (NRS-rat), Normal Goat Serum (NGS), Normal Sheep Serum (NSS), Normal Chicken Serum (NCS), Pig Serum, Horse Serum / Donkey Horse Serum (DHS), and Guinea Pig Serum (for complement fixation tests — CFT). All formats are available in volumes from 1 mL to 100 mL, with bulk supply on request. See the full Animal Sera portfolio for the complete range.