Immune cell receptors are diverse molecules that allow immune cells to recognize and respond to threats, and they can be broadly categorized as follows:
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Pattern Recognition Receptors (PRRs): These receptors recognize conserved molecular patterns on pathogens (PAMPs) and damaged cells (DAMPs).
- Toll-like Receptors (TLRs): A major family of PRRs located on cell surfaces and in endosomes, recognizing various bacterial, viral, and fungal components. For example, TLR4 recognizes lipopolysaccharide (LPS) from Gram-negative bacteria.
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B Cell Receptors (BCRs): Membrane-bound antibodies on B cells that bind to specific antigens, initiating B cell activation and antibody production.
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T Cell Receptors (TCRs): Receptors on T cells that recognize peptide fragments of antigens presented by MHC molecules on other cells. TCRs mediate T cell activation and subsequent immune responses.
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Killer Activating and Killer Inhibitory Receptors (KARs and KIRs): Found primarily on natural killer (NK) cells, these receptors regulate NK cell activity by recognizing molecules on target cells. KARs trigger NK cell killing, while KIRs inhibit it.
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Complement Receptors: These receptors bind to complement fragments (e.g., C3b, C3d) that coat pathogens or immune complexes, facilitating phagocytosis and immune cell activation.
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Fc Receptors: These receptors bind to the Fc region of antibodies, linking antibody-antigen complexes to immune cells and triggering various effector functions like phagocytosis, antibody-dependent cell-mediated cytotoxicity (ADCC), and mast cell degranulation.
In summary, immune cell receptors are critical for recognizing diverse signals and mounting appropriate immune responses. This broad classification encompasses both innate and adaptive immune recognition mechanisms.
