Cytological studies of tissue repair in the human lower respiratory tract

Bronchial brushing procedure for diagnosing pulmonary diseases resulted in cytomorphological changes in epithelial cells including mitotic figures. Cytological studies revealed that the atypical cells derived from the reaction of the so-called tissue repair or regeneration of bronchial epithelium after mechanical injury from the brushing procedure. The findings of the tissue repair cells changed with passage of time after the brushing. On the second day after the initial brushing, atypical cells obtained from the rebrushing at the same site appeared in sheets with basophilic and finely vesicular cytoplasm, enlarged round or oval nucleus, nuclear hyperchromasia, one or more markedly enlarged nucleoli, and occasional mitotic figures. It was sometimes hard to differentiate these cells from malignant cells. On the third day, findings were similar to those observed on the second day except for absence of the mitotic figure. On the fourth and fifth days, atypical cells decreased both in number and abnormality. Non-ciliated columnar cells were frequently found and slight differentiati n in the goblet cells and/or squamous metaplastic cells was sometimes present. On the seventh day, normal ciliated cells dominated. These characteristic findings indicate that activated mitoses and increased cellular metabolism occurred at an early phase after mechanical injury, and the immature epithelial cells became fully differentiated cells within seven days. Similar cytological findings were observed in the initial bronchial brushing specimen obtained from the case with chronic respiratory infection.