The prevalence of allergic rhinitis and asthma has increased in many countries in recent decades. The reason for this increase is not clear but has been largely attributed to environmental factors such as exposure to aerial pollutants and early life events, including the degree of exposure to infectious agents that might affect IgE production. Extensive evidence suggests that the decrease of bacterial and viral infection because of the improvement of living standard and reinforcement of vaccination may have contributed to the development of various allergic diseases. Allergic rhinitis and asthma are dominated by T-helper type 2 (Th2) lymphocyte responses when stimulated by allergens such as house dust mite, animal fur, and grass pollen in releasing interleukin-4, which promotes IgE production by B-lymphocytes.
By contrast, T-helper type 1 (Th1) lymphocytes secrete interferon-7 and interleukin-2, which can inhibit B-cell production of IgE when stimulated by some respiratory infections or immunization with attenuated bacille Calmette-Guerin (BCG) vaccine. The absence of infections in childhood might, according to the microbial stimulation hypothesis, release Th2 immune mechanisms and thus promote allergic diseases.
The tuberculin skin test with purified protein derivative (PPD) is a standard and simple test, and is still widely used to screen for tuberculosis. It is believed that a positive PPD response (5 to 15 mm of induration) indicates past tuberculosis infection, and that a strong PPD response (> 15 mm of induration) is highly suggestive of active tuberculosis. The PPD response is a delayed-type hypersensitivity reaction and is mediated primarily by a Th1 response and is supposed to be suppressed in atopic diseases. Shirakawa et al reported an inverse association between tuberculin responses and atopic disorders in Japanese children. However, other studies have not observed a significant relationship between BCG vaccination during the first year of life and development of atopy in children and adults, assessed either by a questionnaire or by skin-prick testing (SPT) and measurement of serum-specific IgE antibodies. Norwegian investigators studied a group of young adults who had been vaccinated with BCG at the age of 14 years and reported no significant relationship between a positive tuberculin reaction and atopy. Although the evidence for an association between BCG vaccination and atopy is inconsistent, one could question whether the protection provided by BCG vaccination in preventing the development of allergy can extend to adulthood, or whether the memory of the immune system and capability of polarizing T-lym-phocytes may be greater in early life and subsides gradually as one grows up.
On the video below Columbia University Medical Center representative tells about tuberculosis vaccine:
In China, the prevalence of tuberculosis infection is approximately 42 per 100,000 population, the second highest in the world. It is mandatory that BCG vaccination be administered within the first day of birth, and a scar forms later on the vaccination site. We can measure the size of the scar as an indicator of the effect of the BCG vaccination. One study showed that approximately 80% of the subjects had positive tuberculin reactions 3 months after BCG vaccination, which was reduced to 70% and 60%, respectively, 1 year and 10 years after BCG vaccination. We assume that the protection provided by BCG vaccination against tuberculosis infection and development of allergic diseases may be limited to populations immunized in early childhood when substantial modulation of the immune system can occur. Therefore, we investigated the relationship between BCG scars, tuberculin skin responses, and the development of adult bronchial asthma (https://onlineasthmainhalers.com/category/bronchial-asthma), allergic rhinitis, and atopy.