Could asthma and allergy protect against severe COVID-19?

NEW YORK (Reuters Health) - People with asthma and allergies have reduced angiotensin-converting enzyme-2 (ACE2) gene expression and this may offer protection against severe COVID-19 illness, a new study suggests.

SARS-CoV-2, the virus that causes COVID-19, uses ACE2 to infect cells. Studies have shown that higher expression of ACE2 is associated with smoking, diabetes and hypertension, all of which have been tied to increased COVID-19 severity.

The U.S. Centers for Disease Control and Prevention lists asthma as a risk factor for severe COVID-19 illness. However, early case series from China did not include asthma and respiratory allergies as significant risk factors for severe COVID-19 illness.

“We were surprised to learn that the COVID-19 pandemic in China did not seem to impact people with asthma as severely as we would’ve expected it to,” lead investigator Dr. Daniel Jackson of the University of Wisconsin-Madison School of Medicine and Public Health said in a statement.

“Knowing that other risk factors for severe COVID-19 illness like hypertension and obesity lead to increased ACE2 expression, we wanted to determine if patients with allergies and asthma could have reduced ACE2 gene expression as a potential explanation for this unexpected early finding from the outbreak,” he explained.

The researchers analyzed data from three different cohorts of children and adults. In children, allergic sensitization was inversely correlated with ACE2 expression in nasal epithelium regardless of asthma status. In children with asthma, moderate and high allergic sensitization were associated with progressively greater reductions in ACE2 compared with children with no or minimal allergic sensitization. In adults, allergen exposure led to significant reductions in ACE2 expression.

“Given that ACE2 serves as the receptor for SARS-CoV-2, our findings suggest a potential mechanism of reduced COVID-19 severity in patients with respiratory allergies,” the study team writes in the Journal of Allergy and Clinical Immunology.

“However, it is likely that additional factors beyond ACE2 expression modulate the response to COVID-19 in allergic individuals, and elucidation of these factors may also provide important insights into COVID-19 disease pathogenesis.”

They note that additional studies focusing on respiratory allergy, asthma and, perhaps, other allergic disorders are needed to gain a better understanding of the impact of underlying allergy on COVID-19 susceptibility and illness severity.

“The modulation of ACE2 expression by type 2 inflammatory processes suggests the need to comprehensively evaluate the role of type 2 immune regulation in COVID-19 pathogenesis. Further elucidation of these relationships could identify novel therapeutic strategies to more effectively control this pandemic,” they conclude.

SOURCE: Journal of Clinical Allergy and Immunology, online April 22, 2020.