Bead-Antibody Isotype Incompatibility (IP-Western Blot)

Question

Accepted Answer

No or very weak target protein signal despite using adequate antibody concentration, suggesting inefficient antibody capture by the beads due to isotype incompatibility. Common causes: 1) Mouse IgG1 has only moderate/slight affinity for both protein A and protein G beads 2) Mouse IgM requires evaluation with protein A and has strong affinity only for protein A/G mix 3) Rat IgG subclasses (IgG1, IgG2b, IgG2c) have poor or moderate affinity for standard protein A/G beads 4) Human antibody fragments (scFv, F(ab), F(ab')2) require Kappa/Lambda binders instead of protein A/G 5) Chicken antibodies do not bind efficiently to protein A or protein G without bridging antibody Solutions: 1) Consult vendor affinity guide: use protein A/G mix for mouse IgM; use protein G for mouse IgG3, IgG2a, IgG2b 2) For rat antibodies, use protein G beads for IgG2a (strong affinity) or protein A/G mix for other subclasses 3) For human antibody fragments or light chain-specific capture, use PureProteome Kappa and Lambda magnetic beads (mixed 1:1 ratio) 4) When using mouse IgG1, chicken antibodies, or other low-affinity combinations, add bridging antibody or switch to Kappa/Lambda binders 5) Refer to the vendor relative affinity table: SA=Strong Affinity, MSA=Moderate/Slight Affinity, RE=Requires Evaluation