Crystallographic characterization of human eosinophil Charcot-Leyden crystals

Charcot-Leyden crystals: An ancient but never so current discovery

From the first description of Charcot-Leyden crystals (CLCs) to the present, many steps have been taken to understand the mechanisms underlying their formation. In particular, to date not only eosinophils but also mast cells are known to be responsible for the production of CLCs, which represent the crystallized form of Galectin-10. Due to their characteristics, CLCs typically induce a crystallopathy and are responsible for an exacerbation of inflammation. Nasal cytology (NC) has allowed to better understand the correlation between the severity of several rhinopaties and the presence of CLCs in NC samples, which is strictly correlated with an eosinophiles and mast cells infiltration. As a matter of fact, rhinopaties with a mixed eosinophilic-mast cell inflammatory infiltrate, characterized by the presence of abundant CLCs, show a worse prognosis and a higher risk of relapse. This could have important therapeutic implications, since the treatments available today could be exploited to target both eosinophils and mast cells, to reduce the damage induced by CLCs.

Charcot-Leyden crystals within a periapical lesion

Transmission electron microscopy revealed the presence of Charcot-Leyden crystals within a periapical lesion, which was assessed histopathologically as consistent with a periapical granuloma that failed to resolve after conventional endodontic treatment. This paper presents the clinical, radiographic, histological, and ultrastructural findings of this case and discusses their potential clinical significance.

Crystal structure of human Charcot-Leyden crystal protein, an eosinophil lysophospholipase, identifies it as a new member of the carbohydrate-binding family of galectins

BACKGROUND

The Charcot-Leyden crystal (CLC) protein is a major autocrystallizing constituent of human eosinophils and basophils, comprising approximately 10% of the total cellular protein in these granulocytes. Identification of the distinctive hexagonal bipyramidal crystals of CLC protein in body fluids and secretions has long been considered a hallmark of eosinophil-associated allergic inflammation. Although CLC protein possesses lysophospholipase activity, its role(s) in eosinophil or basophil function or associated inflammatory responses has remained speculative.

RESULTS

The crystal structure of the CLC protein has been determined at 1.8 A resolution using X-ray crystallography. The overall structural fold of CLC protein is highly similar to that of galectins -1 and -2, members of an animal lectin family formerly classified as S-type or S-Lac (soluble lactose-binding) lectins. This is the first structure of an eosinophil protein to be determined and the highest resolution structure so far determined for any member of the galectin family.

CONCLUSIONS

The CLC protein structure possesses a carbohydrate-recognition domain comprising most, but not all, of the carbohydrate-binding residues that are conserved among the galectins. The protein exhibits specific (albeit weak) carbohydrate-binding activity for simple saccharides including N-acetyl-D-glucosamine and lactose. Despite CLC protein having no significant sequence or structural similarities to other lysophospholipase catalytic triad has also been identified within the CLC structure, making it a unique dual-function polypeptide. These structural findings suggest a potential intracellular and/or extracellular role(s) for the galectin-associated activities of CLC protein in eosinophil and basophil function in allergic diseases and inflammation.

Detection of Charcot-Leyden crystals by fluorescence microscopy of Papanicolaou-stained smears of sputum, bronchoalveolar lavage fluid, and bronchial secretions

Fluorescence microscopy was used to examine Papanicolaou-stained smears of sputum and other secretions from the respiratory tract. Under these conditions Charcot-Leyden crystals (CLC) appear as bright yellow-green fluorescing needles. The study was performed to determine the value of this approach for the diagnosis of allergic lung diseases. The time taken to detect the crystals was recorded and the sensitivity of fluorescence microscopy for the detection of CLC was compared with light microscopy of the same samples. The data show that fluorescence microscopy is superior to light microscopy for the detection of CLC. The characteristic needle-shaped crystal can be recognized easily and fragments of crystals could be easily identified. In doubtful cases of allergic lung diseases, fluorescence microscopy may be used to supplement light microscopy for the detection of Charcot-Leyden crystals.