Immunoglobulin Fab-fragment

To escape the divalent character of immunoglobulin, Fab fragments which possess only one binding site can be used. Two different methods were described for purification of monovalent F.b fragments from IgG. One is a digestion by papain (Porter, 1959) at an enzyme-to-IgG final ratio of 1 25... 

Figure 1S.6 Enzymatic cleavage of immunoglobulin IgG. The enzyme papain splits the molecule in the hinge region, yielding two Fab fragments and one Fc fragment.

CN immunoglobulin G (human-mouse monoclonal c7E3 clone p7E3VHhCy4 Fab fragment antihuman... 

Blocking Endogenous Tissue Immunoglobulins Homologous to Primary Antibody by Preincubation with Unconjugated Fab Fragments... 

Fig. 9.1 Immunolocalization of Adenosine Receptor A (FITC, green) in mouse myocardium using mouse monoclonal primary antibody after blocking mouse endogenous immunoglobulins by preincubation with unconjugated Fab fragment Goat Antimouse IgG. Red color accounts for cardiomyocytes and erythrocytes autofluorescence captured under illumination with a filter excit ing the autofluorescence in red spectrum. Nuclei are counterstained with DAPI (blue). Courtesy of Stephanie Grote...

Based apparently on the same principle as described above, suitable but rather expensive kits exploiting monovalent Fab fragments to block endogenous tissue immunoglobulins have also been developed commercially, such as Mouse-on-Mouse (M.O.M. ) Kits by Vector Laboratories (http //www.vectorlabs.com/). Three Vector M.O.M. kits are available. These kits use the same blocking technology and biotin-avidin detection format, but offer a choice of using either an enzyme-based or fluorescent-based visualization method. 

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