Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: The coronavirus SARS-CoV-2 has infected more than 600,000 people and has overwhelmed hospital systems around the world. However, the factors mediating fatal SARS-CoV-2 infections are poorly understood. Here, we show that cigarette smoke causes a dose-dependent upregulation of Angiotensin Converting Enzyme 2 (ACE2), the SARS-CoV-2 receptor, in rodent and human lungs. Using single-cell sequencing data, we demonstrate that ACE2 is expressed in a subset of epithelial cells that line the respiratory tract, including goblet cells, club cells, and alveolar type 2 cells. Chronic smoke exposure triggers a protective expansion of mucus-secreting goblet cells and a concomitant increase in ACE2 expression. In contrast, quitting smoking causes a decrease in lung ACE2 levels. Taken together, these results may partially explain why smokers are particularly likely to develop severe SARS-CoV-2 infections, and they suggest that quitting smoking could lessen coronavirus susceptibility.

Cigarette smoke triggers the expansion of a subpopulation of respiratory epithelial cells that express the SARS-CoV-2 receptor ACE2