Final answer:
TLR-9 is primarily expressed on dendritic cells, which are essential in the immune system's response to pathogens. Dendritic cells, macrophages, and B cells can present antigens via MHC II molecules and are involved in phagocytosis, with macrophages also promoting inflammation. Neutrophils are also phagocytic and a key defense mechanism against pathogens.
Step-by-step explanation:
TLR-9 is mainly expressed on c) Dendritic cells. These cells play a crucial role in the immune system by recognizing pathogens and initiating an immune response. Dendritic cells, along with other antigen-presenting cells such as macrophages and B cells, can present antigens via MHC II molecules, which are found only on these specific cells. Macrophages and B cells are also phagocytic cells; they can engulf and digest pathogens. In addition to phagocytosis, macrophages can produce chemicals that promote inflammation, aiding in the body's immune defense against pathogens.
Cytotoxic T lymphocytes (CTLs), which bind MHC molecules on APCs (antigen-presenting cells) via CD8 coreceptors, are another vital component of the immune system, specifically targeting virally infected cells. Neutrophils are also phagocytic and act as first responders to infection, producing cytokines that help destroy and remove pathogens from the body.