Which cells play a critical role in the immune response?

Leukocytes, commonly known as white blood cells, play a vital role in the immune response. They are essential for identifying and combating pathogens, such as viruses, bacteria, and other foreign invaders in the body. There are several types of leukocytes, each with specific functions, including lymphocytes (B cells and T cells) that are crucial for adaptive immunity and phagocytes that engulf and destroy pathogens. This specialized function of leukocytes directly impacts the body's ability to defend itself against infections and diseases.

Platelets, thrombocytes, and erythrocytes do not have a direct role in the immune response. Platelets and thrombocytes refer to the same component of blood involved in clotting and preventing bleeding. Erythrocytes, or red blood cells, are responsible for transporting oxygen to tissues and do not participate in immune functions. Therefore, leukocytes are the key players in the immune response, making them the correct answer.