Final answer:
Natural killer cells use MHC I molecules to identify infected or abnormal cells and initiate a defensive response. MHC class I molecules also aid in the activation of cytotoxic T cells, and for bacterial infections, macrophages are heavily involved in the immune response.
Step-by-step explanation:
The innate immune system component that uses major histocompatibility class (MHC) I molecules directly in its defense strategy is natural killer cells (NK cells). NK cells monitor the levels of MHC I molecules on cells. An unusually low presence of MHC I molecules on a cell can signify that the cell is infected or abnormal, prompting NK cells to target and lyse these potentially dangerous cells.
MHC class I molecules are ubiquitously found on all nucleated cells and play a crucial role in the immune system by presenting endogenous antigens to T cells. The cytotoxic T cells (CTLS), also known as CD8+ T cells, bind MHC molecules on antigen-presenting cells (APCs) via CD8 coreceptors.
For bacterial infections, the macrophages play a significant role in the immune response. They are capable of phagocytizing pathogens and producing chemicals that promote inflammation. Other components such as T cells and antibodies are part of the adaptive immune system, which develops a targeted response to specific pathogens.