TLR4 and allergic rhinitis: However, there is not a clear indication as to the role of TLR4 in asthma nor atopic diseases, with meta-analyses having identified that TLR4 polymorphisms may be either preventative (79) or represent risk factors (53) for development of asthma while TLR4 protein levels are enhanced in the nasal mucosa of patients with allergic rhinitis (55).