Botulinum neurotoxin is used to treat a large number of muscle hyperactivity disorders, including dystonia, spasticity, and tremor; autonomic disorders such as hyperhidrosis, hypersalivation and various bladder disorders; and pain conditions, especially chronic migraine. Aesthetic applications have also become a large indication. Commercially available preparations of Bont/A and BoNT/B are listed.

The active component in all products is BoNT, a di-chain protein of 150 000 daltons. BoNT/A inhibits release of acetylcholine by cleaving the SNARE protein SNAP-25 while BoNT/B cleaves VAMP II. Since BoNT is a foreign protein, the human immune system may respond to it with the production of specific anti-BoNT antibodies (BoNT-AB).

The probability of developing BoNT-AB increases with the amount of BoNT applied at each injection series. Other drug- and patient-related factors might contribute to the immune response. Unspecific activation of the immune system as a possible risk factor for BoNT-AB formation is currently been discussed in connection with COVID-19 vaccination programs. A pre-activation of lymphocytes may have triggered BoNT/A-AB formation. In this chapter, a method is presented for the quantification of BoNT-AB in sera, the immune cell reactions to antigens are described and drug related immune responses are discussed.