Final answer:
SP-D opsonins specifically target bacterial cells by marking them for phagocytosis by cells like macrophages, which are part of the immune system's first line of defense.
Step-by-step explanation:
SP-D opsonins specifically target d) Bacterial cells. Opsonins, such as SP-D, are components of the innate immune system that tag pathogens for destruction. They do not directly interact with any of the body's own cells (like B cells, T cells, or red blood cells). Opsonins make it easier for phagocytic cells, such as macrophages, to recognize, engulf, and destroy pathogens such as bacteria.
- Macrophages are an example of phagocytic cells that can engulf and digest cellular debris and pathogens.
- The adaptive immune response is most directly effective against bacteria through the action of antibodies, which are produced by plasma cells.
- Cytotoxic T cells, a component of the cellular adaptive immunity, work in concert with natural killer cells against virally infected cells.