What component of blood is primarily responsible for immune responses?

The component of blood primarily responsible for immune responses is white blood cells. These cells, also known as leukocytes, play a crucial role in the body's defense mechanism against pathogens such as bacteria, viruses, and other foreign invaders. They do so through various functions, including recognizing and neutralizing these threats, producing antibodies, and coordinating the immune response.

White blood cells can be further categorized into different types, including lymphocytes (which include T cells and B cells), neutrophils, monocytes, eosinophils, and basophils, each with specific roles in the immune system. For instance, lymphocytes are pivotal in adaptive immunity, which involves memory and heightened responses upon re-exposure to the same pathogens.

In contrast, plasma is the liquid component of blood that carries nutrients, waste products, and hormones but does not have a direct role in specific immune functions. Platelets are involved in blood clotting and do not partake in immune responses. Red blood cells are responsible for transporting oxygen and carbon dioxide but do not contribute to the immune defense either. Therefore, the significant involvement of white blood cells in various immune processes makes them the correct answer in this context.