Which of the following is NOT a characteristic of complement?

The correct answer is that complement proteins are not heat stable. Complement proteins are a group of proteins that play an essential role in the immune response, and their functionality is affected by temperature changes. Generally, many of these proteins can become denatured or inactive when subjected to high temperatures, which can hinder their ability to effectively participate in immune processes such as opsonization, lysis of pathogens, and activation of inflammatory responses.

In contrast, complement proteins are indeed designated by numbers, which helps in identifying and studying their specific functions in the immune system. They are also classified as plasma proteins, primarily synthesized by the liver, and are normally present in circulation in inactive forms, ready to be activated in response to infection or injury.