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Sorry, I get confused here. May I ask: "do u mean use the primary Ab and isotype IgG2a as well to gain a more specific binding?" In this setting, secondary Ab would combine to whatever kinds of mouse IgG and yield to everything positive!
In contradiction, IgG2a could compete with 1st Ab to bind with antigen and only if IgG2a, could be named with 'cold drug', is 100 times concentrated than 1st Ab, named 'hot drug', the bound between 1st Ab & antigen could be blocked to the extend of 99%. Am I on the right track? So this is all about giving a non-specific binding?