What is the main purpose of white blood cells in the immune system?

White blood cells, or leukocytes, are crucial components of the immune system primarily tasked with defending the body against infection and disease. Their main purpose involves the identification and elimination of pathogens such as bacteria, viruses, and other foreign invaders that can compromise health.

Different types of white blood cells play specific roles in this defense mechanism. For example, phagocytes engulf and digest pathogens, while lymphocytes (such as B cells and T cells) are involved in recognizing specific invaders and orchestrating targeted immune responses. B cells produce antibodies that neutralize toxins and pathogens, while T cells can directly kill infected cells or help regulate the immune response.

The other options focus on functions that do not relate directly to the immune defense. Transporting oxygen is the primary role of red blood cells, regulating blood clotting is primarily managed by platelets and clotting factors, and maintaining fluid balance in tissues relates to lymphatic system functions and not directly to white blood cells. Therefore, the central role of white blood cells in defending against infection and disease is what sets them apart in the framework of the immune response.