Leukocytes, also known as white blood cells, are an important part of our immune systems. They detect and help fight infections and other diseases. In the body, leukocytes are made up of several categories, each with its own distinct functional characteristics. The following are some of the functions that leukocytes perform:

• Producing antibodies to protect against disease-causing organisms
• Recognizing and engulfing particles, such as bacteria and viruses
• Eliminating harmful substances in the body, such as toxins and waste materials
• Producing lymphocytes that can differentiate between foreign and self
• Assisting in the healing of damaged tissues

Of the functional characteristics listed above, the one that is not a characteristic of leukocytes is producing lymphocytes that can differentiate between foreign and self. Lymphocytes are a type of white blood cell that is involved in recognizing and destroying invading organisms. However, they do not differentiate between foreign and self, unlike other types of leukocytes. Instead, they recognize and attack specific types of antigens, which are molecules that the body identifies as foreign.

In conclusion, leukocytes are an important part of our immune systems and perform several functions, including producing antibodies, recognizing and engulfing particles, eliminating harmful substances, and assisting in the healing of damaged tissues. The characteristic that leukocytes do not possess is the ability to differentiate between foreign and self.