Final answer:
Complement receptors are part of the immune system and are specific types of cell-surface receptors that bind to components of the complement system. The four main complement receptors are CR1, CR2, CR3, and CR4, with their ligands being C3b and C4b for CR1, C3d for CR2, and iC3b for CR3 and CR4.
Step-by-step explanation:
The student is asking about complement receptors and their ligands. Complement receptors are part of the immune system and bind to components of the complement system. The main complement receptors to be familiar with are: CR1, CR2, CR3, and CR4. Their respective ligands are C3b and C4b for CR1, C3d for CR2, iC3b for CR3, and iC3b for CR4. These receptors are crucial for immune functions such as phagocytosis, immune complex clearance, and modulation of B and T cell responses.
In relation to cell-surface receptors and signaling, these complement receptors are examples of cell-surface receptors, which bind to external ligands without the ligands having to enter the cell. This feature allows quick and specific responses to surrounding molecular signals. The ligand-binding domain, the membrane-spanning region, and the intracellular domain are three main components of such receptors. The interaction is highly specific; a receptor typically binds only to its matching ligand, as in the case of complement receptors binding to elements of the complement system.