Rhinoviruses infect the epithelial cells of the respiratory tract. The viruses can be grouped according to the epithelial cell receptors to which they bind. Major-group viruses bind to the cell surface receptor ICAM-1 for entry (1); minor-group viruses bind to the unrelated low density lipoprotein (LDL) receptor (2). This receptor difference turns out to be a key factor in how these viruses interact with the immune system. Major-group viruses also bind the ICAM-1 molecule expressed on macrophages, dendritic cells, and other immune cells (3). This attachment triggers a host of changes in the immune cells that effectively dampens the immune response. The immune cells produce anti-inflammatory signals (4); they are slower to activate the T cells in the lymph nodes that attack the viruses (5); and they reduce the production of antibodies and activation of memory B and T cells that protect the host against reinfection (6). Because the minor-group viruses cannot bind the ICAM-1 molecule on immune cells, they do not suppress the immune system.
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