Clara’s Cell

Club cells , are known as Clara cells by their discoverer or also as bronchiole exocrine cells ; Are cells with dome morphology and short microvilli found in the small airways called bronchioles of the lungs. ^{1 2}

Club cells are located in the simple ciliated epithelium. These cells secrete surfactant in the form of glucosaminoglycans to protect and lubricate the inside of the bronchiole. This cell type increases as the number of goblet cells decreases.

One of the main functions of club cells is to protect the bronchiolar epithelium. This is achieved by secreting a small variety of products, including the uteroglobin or protein secreted by the club cells together with a solution with a composition similar to that of the pulmonary surfactant. Club cells are also responsible for the detoxification of harmful substances inhaled into the lungs by the cytochrome P450 enzymes found in their smooth endoplasmic reticulum . They also act as stem cells as they multiply and differentiate into ciliated cells, to regenerate the bronchiolar epithelium.

Mechanism

Respiratory bronchioles represent the transition from the conducting portion to the respiratory portion of the respiratory system. These narrow channels are usually less than 2 mm in diameter and are covered by a simple cuboidal epithelium, with hair cells and club cells that are not exclusive to the bronchioles. In addition to being structurally diverse, club cells are also functionally variable. An important function is the synthesis and secretion of the material that covers the bronchial lumen. Its composition includes glycosaminoglycan s, proteins such as lysozymes , and a conjugate of the secretory portion of IgA antibodies. These play an important defensive function, and also contribute to the degradation of the mucus produced in the upper conductive sections. The heterogeneous nature of the dense granules in the cytoplasm of the club cell suggests that they may have some additional function to the secretory one. They may contain lysosomal enzymes that perform a digestive function, both for defense: they trap toxins and degrade them via cytochrome P-450 (particularly CYP4B1, which is present only in club cells) of its smooth endoplasmic reticulum; As for the recycling of products of secretion. Club cells are mitotically active. They divide and differentiate to form both ciliated and non-ciliated epithelial cells.

Role in disease

Club cells contain tryptase, which is believed to be responsible for the cleavage of the hemagglutinin surface protein from influenza A virus, thereby making it responsible for the activation and symptoms of the flu. ³ When l7Rn6 protein is disrupted in mice, these mice show emphysema severe birth resulting in a disruption in the Golgi apparatus and the formation vesicular structures within the club aberrant cells. ⁴ The serum proteins of the club cell are used as a biomarker of lung permeability. Exposure to particulate air contamination may compromise the integrity of the pulmonary epithelium and result in a rapid increase in permeability of the epithelial barrier, as reflected in the increased serum concentration of club cell proteins . ⁵

Nomenclature

Club cells were formerly called Clara cells, as they were first described by Max Clara (1899-1966).
In 1937, Max Clara was an active member of the Nazi Party and used tissues taken from victims executed by the Third Reich for his investigation - including the work that led to his discovery of Clara cells. ⁶ In May 2012, the editorial staff of most magazines major pulmonology (including the American Thoracic Society, the European Respiratory Society and the Journal of the American College of Chest Physicians) concluded that continued use of the eponym “Clara” would Equivalent to honoring him; Therefore introduced a policy of nomenclature change, which began on January 1, 2013. ⁷ The term “cell of Clara” remained in parallel for 2 years with that of “club cell”. After that period, the terms “Clara cell” and “Clara protein secretory cell” were replaced by “club cell” and “protein secretory club cell” respectively. ⁸ In Europe this nomenclature takes a little longer to become popular.

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