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1. Macrophages - They are a type of white blood cell that engulfs and digests cellular debris, foreign substances, microbes, cancer cells in a process called phagocytosis 2. Neutrophils - They are the most common type of white blood cells and are part of the innate immune system, which is non-specific and attacks any invading pathogens. 3. NK Cells - Natural Killer (NK) cells are a type of lymphocyte that can kill cells without the need for activation by specific antigens. They are unique in their ability to recognize cells that do not express MHC class I molecules, which are usually indicative of an infection or malignancy. 4. Interferon - It is a type of protein that is produced and released by host cells in response to the presence of, for example, viruses or other harmful microorganisms. Its role is primarily anti-viral.

From the understanding of the roles of the different components of the immune system, it is evident that NK cells are the ones that interact directly with the MHC class I molecules during immune responses. The lack of these molecules signals NK cells to kill the affected cells. The MHC class I molecules play a crucial role in the defense strategy of NK cells.