In conclusion, isotype controls are useful for demonstrating that there was poor blocking of the cells. They should never be used to determine or set positivity in fully stained samples.

Do I need an isotype control?

The secondary could also have altered binding properties in isolation compared to binding with the appropriate isotype control. Instead, ideally, the negative control used for IHC should mimic the exact concentration and isotype of the primary antibody, which is why an isotype control is the most appropriate choice.

Why do we need isotype control?

Isotype controls are used as negative controls to help differentiate non-specific background signal from specific antibody signal. Depending upon the isotype of the primary antibody used for detection and the target cell types involved, background signal may be a significant issue in various experiments.