Chitin, the second most abundant polysaccharide in nature after cellulose, consist exoskeleton of lower organisms such as fungi, crustaceans and insects except mammals. Recently, several studies evaluated immunologic effects of chitin in vivo and in vitro and revealed new aspects of chitin regulation of innate and adaptive immune responses. It has been shown that exogenous chitin activates macrophages and other innate immune cells and also modulates adaptive type 2 allergic inflammation. These studies further demonstrate that chitin stimulate macrophages by interacting with different cell surface receptors such as macrophage mannose receptor, toll-like receptor 2 (TLR-2), C-type lectin receptor Dectin-1, and leukotriene B4 recepptor (BLT1). On the other hand, a number of chitinase or chitinase-like proteins (C/CLP) are ubiquitously expressed in the airways and intestinal tracts from insects to mammals. In general, these chitinase family proteins confer protective functions to the host against exogenous chitin-containing pathogens. However, substantial body of recent studies also set light on new roles of C/CLP in the development and progression of allergic inflammation and tissue remodeling. In this review, recent findings on the role of chitin and C/CLP in allergic inflammation and tissue remodeling will be highlighted and controversial and unsolved issues in this field of studies will be discussed.
Animals ; Chitin/*immunology ; Chitinase/*immunology ; Glycoproteins/*immunology ; Humans ; Hypersensitivity/*immunology ; Inflammation/*immunology

What makes a certain molecule to elicit allergic responses? It has been a long-running question in allergology and immunology. Molecular properties of allergens have been characterized for last 30 years. However, it has become evident that allergen alone cannot induce allergic reactions. The way of introduction to the immune system and adjuvant-like activity of concomitantly administered molecules are thought to be important. Physical properties which facilitate delivery may characterize inhalant allergens. Buoyant and sticky antigens with small molecular weight (10-50 kDa) may be carried by particles and remain airborne. Most allergens could be grouped into allergen families according to biochemical properties. Protease, lipid-binding/transfer protein, actin-binding protein, Ca-binding protein, α-amylase/trypsin inhibitor, and pectate lyase account for a significant number of allergens. Biochemical properties which enhance the activation of Th2-immune responses could be another characteristic of allergens. The protease activity of allergens can help break the skin barrier or mucus membrane and its penetration into the body. The capacity of allergen to carry immunologically active substances could increase the allergenicity. Lipid-binding ability is believed to play a role in this aspect. Danger signals, such as endotoxin, β-glucan, and chitin derived from the pathogens, commensals and from the environment can enhance the immune response to allergens. The known characteristics of food allergens are resistance to heat, acid, and digestive enzymes. However, food processing makes it more complex. Understanding the intrinsic properties of allergens may shed light on the mechanisms on the pathogenesis of allergic disorders and improve the diagnostic and therapeutic approaches.
Allergens* ; Allergy and Immunology ; Chitin ; Food Handling ; Hot Temperature ; Humans ; Hypersensitivity ; Immune System ; Membranes ; Molecular Weight ; Mucus ; Particulate Matter ; Pollen ; Pyroglyphidae ; Skin

Development of alternatively activated (M2) macrophage phenotypes is a complex process that is coordinately regulated by a plethora of pathways and factors. Here, we report that RBP-J, a DNA-binding protein that integrates signals from multiple pathways including the Notch pathway, is critically involved in polarization of M2 macrophages. Mice deficient in RBP-J in the myeloid compartment exhibited impaired M2 phenotypes in vivo in a chitin-induced model of M2 polarization. Consistent with the in vivo findings, M2 polarization was partially compromised in vitro in Rbpj-deficient macrophages as demonstrated by reduced expression of a subset of M2 effector molecules including arginase 1. Functionally, myeloid Rbpj deficiency impaired M2 effector functions including recruitment of eosinophils and suppression of T cell proliferation. Collectively, we have identified RBP-J as an essential regulator of differentiation and function of alternatively activated macrophages.
Animals ; Cell Polarity ; drug effects ; genetics ; immunology ; Cell Proliferation ; drug effects ; genetics ; Chitin ; immunology ; pharmacology ; Eosinophils ; cytology ; immunology ; Gene Expression Regulation ; drug effects ; immunology ; Immunoglobulin J Recombination Signal Sequence-Binding Protein ; genetics ; immunology ; Macrophage Activation ; drug effects ; genetics ; Macrophages ; cytology ; immunology ; Mice ; Mice, Transgenic ; T-Lymphocytes ; cytology ; immunology