Fab Fragment Secondary Antibodies
Blocking of endogenous immunoglobulins
Monovalent Fab fragments of affinity-purified secondary antibodies are offered to block endogenous immunoglobulins, to cover immunoglobulins when double labeling primary antibodies from the same host species, or to Fab-label primary antibodies prior to incubation with the experimental sample.
Our partner Jackson ImmunoResearch offers a comprehensive portfolio of Fab Fragment Affinity‑Purified Antibodies.
Monovalent Fab Fragments of Affinity-Purified Secondary Antibodies
The Fab fragment antibodies from Jackson ImmunoResearch are generated by papain digestion of whole IgG antibodies to remove the entire Fc fragment, including the hinge region. These antibodies are monovalent, containing only a single antigen binding site. The molecular weight a Fab fragment is about 50 kDa. They can be used to block endogenous immunoglobulins on cells, tissues or other surfaces, and to block the exposed immunoglobulins in multiple labeling experiments using primary antibodies from the same species.
Why Use Fab Fragments?
Divalent (whole IgG or F(ab')2 fragment) antibodies are not recommended for blocking because they have two antigen binding sites. After binding endogenous IgG or the first primary antibody, some antigen binding sites on a divalent secondary antibody may remain unoccupied, which could capture a primary antibody introduced in a subsequent step, resulting in background staining or apparent signal overlap.
The use of monovalent Fab fragments avoids this problem: Each Fab fragment has only a single antigen binding site (i.e. they are monovalent), and they are non-precipitating. Monovalent Fab fragments can thus be used to block endogenous immunoglobulins in tissue sections or on cell surfaces, to cover (block) immunoglobulins when double labeling primary antibodies from the same host species, or to Fab-label primary antibodies prior to incubation with the experimental sample.
Fab Fragments Can Be Utilized in Three Key Ways:
Blocking Endogenous Immunoglobulins to reduce background staining
Background staining may be observed if a labeled secondary antibody is not adsorbed to minimize recognition of endogenous tissue Ig. When a primary antibody is the same species as the tissue under study (e.g. mouse primary used on mouse tissue), blocking endogenous Ig suppresses the off-target signal.
Double labeling primary antibodies from the same host species
Monovalent Fab Fragment Affinity-Purified Antibodies can as well be used for blocking and double labeling primary antibodies from the same host species and class of immunoglobulins.
Label primary antibodies in solution as an alternative to conjugation with FabuLight™ antibodies
FabuLights can be used to label Fc domains of fusion proteins, or cell surface immunoglobulins, without cross-linking or activating cells. Labeling with Fab Fragments can be an alternative.
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With more than 8.500 whole IgG and F(ab‘)2 secondary antibodies in our portfolio you will always find antibodies optimally suited for your immunoassay. Our selection includes products from renowned international manufacturers such as Jackson ImmunoResearch and Southern Biotech as well as, additionally, approx. 1,500 qualitatively outstanding products under the dianova label. Our online selection guide helps you to select the right secondary antibody in six steps.