Smoking during pregnancy the immune system play a role in fetuses and young children

Smoking in pregnant women not only disrupts the development of airway fetus but also interfere with the immune system, which may explain the relatively higher frequency, from birth to a child born of a mother who smokes, the respiratory infections, asthma and other lung diseases allergic in nature, according to an Australian study published in the journal "European Respiratory Journal" (ERJ).

Tobacco: primary cause of respiratory infections

We know that the new-born to smoking mothers are twice more prone to respiratory infections than those whose mothers did not smoke during pregnancy. An even more disturbing that this type of infection is the leading cause of infant mortality in developing countries difference.

However, no prospective study did not allow to explain the increased fragility of the newborn.

It is to fill this gap that Susan Prescott and colleagues of the research unit in pediatrics and child health at the University of Western Australia in Perth, decided to launch the study that they publish the results in ERJ.

The basis of their work, a simple hypothesis: if these children are more vulnerable to infections is that the smoke from their mothers during pregnancy could interfere with the development of their immune system.

"More precisely, says Susan Prescott, we thought especially congenital or innate immune system, which is based on the defenses of the newborn until its immune system develops acquired, will become increasingly powerful as and measuring contacts with antigens ".

In this context, Australian researchers have focused their attention on a special class of biological receptors, "Toll-like receptors" or TLR, whose task is to detect the microbes and transmit alarm signals to the system immune destroy them. They are found on the surface of many circulating blood cells involved in the immune response.

These TLRs are of even greater interest they are an important interface between innate and acquired immunity. They work, in fact, in the immediate responses (innate immunity) of the body of pathogens, being able to recognize all kinds of intruders bacterial, viral, fungal or parasitic, even though they don ' have never been in contact with them previously.

Clinging to it, the TLR set off the immune processes and the production of various compounds to destroy or exclude stressors, including cytokines.

But TLRs also have a regulatory action programming acquired immune function. When activated, they open signaling pathways that are involved in the activation of antigen presenting cells and regulatory T cells, two types of cells that play a key role in adaptive immunity.

Lower immune

The Australian study has been to compare the immune responses of the blood of 60 newborns whose mothers smoked during pregnancy (average of 16 cigarettes per day) with those of 62 other infants whose mothers had either been non- smoking or had quit smoking during pregnancy.

The smoking habits of the mothers was assessed through questionnaires and verified by measuring blood levels of cotinine, the main marker of nicotine, both in women and in the cord blood at birth.

The researchers measured the expression of several cytokines associated with four specific TLR, an approach quite original. "This is a prospective study examining the effects of smoking during pregnancy on these aspects of the innate immune function of the newborn," said Paul Noakes, first author of the article in the ERJ.

An original approach has paid off, as Australian researchers have found that maternal smoking causes a significant alteration in the production of interleukin 6 and tumor necrosis factor alpha (TNF-a), two inflammatory cytokines respectively produced by antigen-presenting cells and mononuclear cells such as lymphocytes.

"We also observed a significant decrease in production of interleukin-10, a regulatory cytokine produced preferentially by antigen-presenting cells in the context of microbial stimulation," said Susan Prescott.

This study thus shows that fetal exposure to cigarette smoke during pregnancy is associated with abnormalities on the one hand, weaken the innate defenses and, on the other hand, inhibit the maturation of the acquired immune system.

A link with the theory of hygiene

These results already strong statistically when taken raw, still remain when confounding factors are taken into account in the analysis. Indeed, neither the existence of allergy in the mother, or the socio-economic status of the household, or the use of illicit drugs (marijuana or ecstasy, for example) changes significantly alter the responses of the innate immune system associated with stimulation of TLRs.

These data demonstrate that in addition to its well-known on the development of airway deleterious effect fetus, maternal smoking also has significant effects on immune maturation.

This discovery is important because it may explain, at least in part, the increased infections seen in children of smoking mothers.

This could be correlated to the hygiene theory, which means that early immune responses to microbial agents play a prominent role in the maturation and orientation of the immune system. Because when microbial stimulation occurs and leads to the normally expected reactions, there is an inhibition of signaling pathways that lead to allergic reactions.

"Our results suggest that smoking during pregnancy can adversely affect the immune programming and may increase the risk of subsequent development of allergic manifestations. Moreover, it is a track that we intend to explore in other work, "concludes Paul Noakes.