An Overview of Cluster of Differentiation 14 (CD14) and its Possible Roles in Allergic Diseases

Abstract

Allergic rhinitis (AR) is a common condition. Estimates of its prevalence vary widely but good epidemiologic studies suggest that 20 to 30% of adults and up to 40% of children are affected¹. Symptoms can have significant negative impact on the patients quality of life, often interfere with sleep, and contribute to poor performance at work and school. In approaching the patient with rhinitis symptoms, clinicians must distinguish AR from non-AR (NAR) and nasal symptoms due to mechanical factors but not miss the presence of local nasal allergy. Treatment for more severe disease should employ anti-inflammatory as well as symptomatic medication, and allergy immunotherapy (AIT) should be strongly considered for not only its effectiveness but also its disease-modifying effects. The main challenges in AR relate to its treatment. Symptomatic and topical anti-inflammatory medication is often not fully effective, and AIT can be inconvenient and expensive, and there is much room for improvement in both forms of treatment. The cluster of differentiation (CD14) is a human gene. The protein encoded by this gene is a glycosylphosphatidylinositol (GPI)- anchored molecule expressed mainly on cell surface of macrophages and monocytes. The x-ray crystal structure of human CD14 protein shows a monomeric, bent solenoid molecule with a hydrophobic amino-terminal pocket that can bind to many acylated ligands. CD14 acts as a pattern recognition receptor that promotes innate immune responses to infection by sensitizing host cells to bacterial LPS (endotoxin), lipoproteins, lipoteichoic acid, and other acylated microbial products. It allows delivery of these microbial products to many TLR signaling complexes which then induce intracellular proinflammatory signaling cascades after ligand binding. Many research works have studied the role of CD14 in different allergic phenotypes. Results of these studies were controversial, as some studies have found that the sCD14 level in certain allergic diseases was significantly higher in periods of illness than its level at recovery period. While other studies reported inversely relationship between serum sCD14 level and certain allergic phenotypes. Also, up till now, few studies have focused on the association between serum sCD14 level and the severity of allergic diseases