What does the immune system include?

Immune cells are a group of specialized cells that defend against foreign substances and help maintain tissue stability and integrity through various mechanisms. They can be classified into natural killer (NK) cells, B cells, T cells, and dendritic cells. Each of these cell types has distinct functions, yet they all belong to a broader category of immune cells involved in antibody-mediated immunity. Natural killer (NK) cells are a unique type of immune cell capable of recognizing and destroying malignant cells, as well as inhibiting the replication of viruses, bacteria, and other external pathogens. B cells are specialized immune cells that produce and secrete antibodies to bind to external antigens, thereby neutralizing foreign substances. Additionally, B cells can generate specific antibodies tailored to combat particular invaders, such as specific viruses or bacteria. T cells are primarily divided into two types: helper T cells and regulatory (suppressor) T cells. These cells play key roles in activating B cells, cytotoxic cells, and other antigen-presenting cells, enhancing immune system activity for more effective defense against invading agents. Lastly, dendritic cells capture signals from other immune cells and release signaling molecules to promote robust and coordinated immune responses. The presence and function of these cells are crucial factors enabling the immune system to effectively protect specific tissues or cells from external threats.