Asthma is more often diagnosed in women than in men, although in childhood there are more boys among asthmatics than boys. Researchers have decided to explain what makes men suffer from asthma much less often than women at a later age.
Initially, it was suspected that female sex hormones (estrogens and progesterone) may promote the development of an immune response in the bronchi. It turned out, however, that testosterone suppresses the secretion of pro-inflammatory molecules responsible for the development of asthma, and the female sex hormones neither stimulate nor inhibit the secretion of cytokinins.
Wheezing epidemic
Asthma alone is a disease characterized by chronic inflammation of the airways that can manifest as wheezing, chest tightness or coughing of varying severity. Inflammation mainly affects the bronchi that are narrowed in asthma. Bronchoconstriction may be due to excessive muscular contraction, the presence of mucus in the bronchi or swelling of their walls. How strongly the bronchi are constricted, i.e. how large are the impediments in the exhalation of air flow, measured using a spirometer.
Since the 1970s, the number of asthmatics has been increasing steadily, and according to 2011, around 235 to 300 million people suffered from asthma worldwide, and 250,000 were the cause of death for 250,000 people. Many factors influence the development of asthma, including exposure to allergens, the frequency of passing of viral infections in childhood, air pollution, smoking and the coexistence of other autoimmune diseases. Now it turns out that sex hormones may also have an impact on the development of asthma.
The percentage of asthma patients in both sexes varies with age. Before puberty, boys suffer from asthma about one and a half times more often than girls, after puberty the proportions are reversed and women are twice as likely to suffer from asthma than men. In the elderly (i.e. for postmenopausal women), the percentage of women and men suffering from asthma is slowly evolving.
Testosterone dial
In a study of the influence of sex hormones on the development of asthma, the researchers focused on one type of cells known to be involved in disease progression - on natural lymphoid cells (ILC-2). These cells secrete cytokinins, molecules that stimulate inflammation in the bronchi, and help to increase the production of mucus, making it difficult for the patient to breathe.
In the first stage of the experiment, the researchers studied blood samples from people suffering from asthma and healthy people. They proved that in the bloodstream of asthmatics, the number of ILC-2 cells is definitely higher than in healthy people, but in general there were more cells in women than in men. The first working hypothesis was that female sex hormones could be responsible for stimulating the formation of this particular type of immune cells. Therefore, the researchers decided to check (already on the culture of mouse cells) how the addition of sex hormones in the environment will affect the production of proinflammatory cytokinins.
When female sex hormones (progesterone and estrogens) were added to the mouse-cell culture of ILC-2, it was not observed to affect these cells in any way or the amount of inflammation molecules they produce. In turn, the addition of testosterone to the culture caused inhibition of cytokinin production by ILC-2 cells. It can therefore be concluded that testosterone is protective against bronchi and prevents the development of asthma in adult men.
Of course, the observed relationship is just one of many reasons for the development of asthma. However, it allowed to explain the mystery bothering doctors for many years.
Based:
J.-Y. Cephus et al.,Testosterone Attenuates Group 2 Innate Lymphoid Cell-Mediated Airway Inflammation, Cell Reports 21 (9) (2017) 2487 - 2499