Which primary receptor is responsible to bind coronaviruses?

Coronaviruses utilize specific host cell surface proteins to facilitate viral entry and membrane fusion. The spike protein (S) of the virus has a high affinity for specific enzymes located on human epithelial cells. This binding triggers endocytosis or direct fusion, allowing the viral RNA to enter the cytoplasm. The distribution of these receptors determines the tissue tropism of the infection. Rationale: A. CD40 receptors are members of the tumor necrosis factor receptor superfamily found on antigen-presenting cells. They play a critical role in T-cell dependent B-cell activation and inflammatory responses. While important for the immune response to viruses, coronaviruses do not use CD40 as their primary entry portal. B. Complement receptors bind to fragments of complement proteins (like C3b) to facilitate the clearance of immune complexes and pathogens. They are part of the innate immune system and assist in phagocytosis. They are not the specific targets for the spike protein attachment mechanism used by coronaviruses. C. ACE-2 (Angiotensin-Converting Enzyme 2) is the primary functional receptor for coronaviruses like SARS-CoV and SARS-CoV-2. The viral spike protein binds to the peptidase domain of ACE-2 on host cells. This receptor is highly expressed in the alveolar epithelium, explaining the severe respiratory symptoms associated with these infections. D. Chemokine receptors are G-protein coupled receptors that guide leukocyte migration during inflammation. While some viruses, such as HIV, utilize specific chemokine receptors (like CCR5 or CXCR4) as co-receptors for entry, coronaviruses primarily rely on carboxypeptidases like ACE-2 rather than the chemokine receptor system.