Which type of cells primarily participates in the humoral immune response?

The humoral immune response is primarily mediated by B cells, which are a type of white blood cell. B cells are responsible for producing antibodies, which are proteins that specifically target and neutralize pathogens like bacteria and viruses. When B cells encounter an antigen that matches their specific receptors, they become activated, proliferate, and differentiate into plasma cells. These plasma cells then secrete large quantities of antibodies into the bloodstream, providing the body with a means to effectively recognize and eliminate the invading pathogens.

While T cells play critical roles in the immune response, particularly in cell-mediated immunity, they do not produce antibodies and thus are not directly involved in the humoral immune response. Natural killer cells are part of the innate immune system and focus on destroying infected or cancerous cells rather than facilitating antibody production. Macrophages are important for phagocytosis and presenting antigens to T cells but do not themselves produce antibodies like B cells do. Therefore, B cells are the key players in the humoral immune response, making them the correct choice in this context.