What type of cells are primarily involved in the immune response and include both T and B cells?

Lymphocytes are the primary type of cells involved in the immune response, and they include both T cells and B cells. Lymphocytes play a crucial role in the adaptive immune system; T cells are responsible for directly attacking infected cells or helping other immune cells, while B cells produce antibodies that target specific pathogens.

Granulocytes, monocytes, and stem cells do not fulfill this role. Granulocytes are a type of white blood cell that primarily deals with acute inflammatory responses and are not specifically involved in the adaptive immune response like lymphocytes. Monocytes can differentiate into macrophages and dendritic cells to help in the immune response but are not the main players in that adaptive response as T and B cells are. Stem cells are undifferentiated cells that can develop into various cell types but do not actively participate in the immune response themselves. Thus, lymphocytes are the correct group of cells associated with both T and B cells in the immune system.