Pollution's Impact: Weakened Immunity And Health Risks

Air pollution is a serious and common public health concern associated with growing morbidity and mortality worldwide. The toxic effects of air pollution have been extensively studied, with a particular focus on the respiratory system. However, air pollution can also influence the immune and nervous systems and may have a significant adverse impact on them.

Air pollution can be defined as the introduction of chemicals, particulate matter, or biological materials into the atmosphere, which may cause harm or discomfort to humans and other living organisms, or cause damage to the environment. The primary site of exposure to air pollution is the respiratory tract following inhalation. The respiratory tract, from nasal passages down through the airways to alveolar gas exchange units in the lungs, represents the prime interface between the immune system and the airborne environment.

The immune system itself consists of multiple types of immune cells that act together to generate (or fail to generate) immune responses. Inadequate and excessive immune responses underlie diverse pathologies such as serious infections, metastatic malignancies, and autoimmune conditions. Therefore, understanding the effects of air pollution on the immune system is vital to understanding how pollution causes disease, and how that pathology could be abrogated.

The effects of air pollution on the immune system are mainly pro-inflammatory and could include direct oxidative effects or induction of reactive oxygen species. Some variability in these effects was shown among the different exhausts and particles investigated, suggesting that distinct physiochemical properties could arise from different materials generated and collected in specific conditions.

The mechanisms underneath the health effects of air pollution are mainly referable to a direct or indirect reactive oxygen and nitrogen species production causing oxidative stress with the activation of inflammatory pathways that lead to an inflammatory status characterised by cytokine production and immune cell activation.

Air pollution can cause oxidative stress and inflammation in the lungs

Air pollution can trigger cellular signalling pathways, including Toll-Like Receptors (TLRs), reactive oxygen species (ROS) sensing pathways, and poly-aromatic hydrocarbon (PAH) sensing pathways. These pathways, in turn, activate pro-inflammatory intracellular signalling cascades, such as NFκB and MAPK pathways.

TLRs are a type of cellular receptor designed to sense pathogen-associated molecular patterns (PAMPs) of potentially infectious microorganisms and other noxious stimuli, and it is notable that pollution can trigger these receptors. The ability of urban PM to stimulate cells through TLRs is thought to be due to the particles containing microbial molecules such as lipopolysaccharide (LPS) and fungal spores, that are natural ligands for TLRs, and also particles inducing production of host-derived molecules that can act as alternative agonists for TLRs, such as oxidised phospholipids and nucleic acids (from cellular damage). LPS stimulates cells through Toll-Like Receptor 4 (TLR4) and PM has been shown to stimulate cells through the TLR4 pathway. However, the proportion of PM-induced cell stimulation that is through different TLRs may differ between cell types and PM types.

Oxidative stress can induce NFκB and AP-1 signalling, as well as transcription of genes containing the antioxidant-responsive element (ARE) promoter. Nrf2 is the major transcription factor acting on ARE promoter sequences to enhance expression of antioxidant genes. Keap1, which binds intra-cytoplasmic Nrf2 and inhibits its translocation to the nucleus to act on ARE sequences, has a high cysteine content, and reactive oxygen species can directly modify these cysteine residues, reducing binding of Keap1 to Nrf2, allowing translocation of Nrf2 to the nucleus.

Oxidative stress generates intracellular danger signals that can induce inflammasome responses, such as NLRP3, which has been shown to be activated by PM in epithelial cells, including the production of IL-1β.

The composition of ambient PM varies both geographically and temporally, depending on the mix of sources at any location at any given time. It contains metals, elemental carbon and organic carbon (both in hydrocarbons and peptides), sulphates and nitrates, as well as other constituents.

PM can generate free-radical oxidants (reactive oxygen species) in both cellular and acellular experimental systems, and ambient particulate matter is well known to cause oxidative stress and reduction of endogenous antioxidants.

In addition to the general pro-inflammatory nature of these effects, many studies suggest an action of air pollution to augment Th2 immune responses and perturb anti-microbial immune responses.

Air pollution can affect the skin, leading to conditions such as acne, eczema, and skin cancer

Air pollution can have a detrimental impact on skin health, leading to various conditions such as acne, eczema, and potentially even skin cancer.

Acne is a common skin disease that affects people of all ages, with a peak prevalence in teenage years. Air pollution, particularly exposure to particulate matter, volatile organic compounds, ozone, nitrogen dioxide, and sulfur dioxide, has been linked to the worsening of acne symptoms. Studies have shown that air pollution can alter the quality of sebum excreted on the skin, leading to oxidative stress and inflammation, which are key factors in the development and progression of acne.

Eczema, also known as atopic dermatitis, is another skin condition influenced by air pollution. It is characterized by dry, itchy skin and can be triggered by exposure to certain pollutants. Fine particulate matter, sulfur dioxide, and sulfate are among the pollutants associated with an increased risk of developing eczema symptoms.

While the direct link between air pollution and skin cancer requires further investigation, pollution can contribute to oxidative stress and inflammation in the skin, which are risk factors for skin cancer. Additionally, air pollution can generate reactive oxygen species and compromise the skin's antioxidant defenses, potentially creating an environment conducive to the development of skin cancer.

The impact of air pollution on the skin is a growing area of concern, and it is important to consider pollution as a risk factor for various skin disorders. Protecting the skin with appropriate cleansing routines, moisturizers, and sun protection is crucial to mitigate the negative effects of air pollution.

Air pollution can cause neuroinflammation and neurotoxicity, potentially contributing to conditions such as autism and Alzheimer's disease

Air pollution is a complex mixture of environmental toxins that can assault the central nervous system (CNS) through several pathways. It is comprised of gases, metals, organic compounds, and particulate matter (PM), with particle pollution and ground-level ozone being the most widespread health threats.

The CNS effects of air pollution are chronic and can take years to accumulate pathology. The primary pathways through which air pollution impacts the brain are:

• Systemic inflammation: Peripheral impact on the brain. Air pollution can cause systemic inflammation, which can lead to neuroinflammation and neuropathology.
• Particle effects: Size matters. Ultrafine and fine particles can penetrate lung tissue, reach the capillaries and circulating cells, and enter the brain.
• Adsorbed compounds: The Trojan Horse Effect. The toxic compounds adsorbed on the surface of particles may act as an effective delivery system for environmental toxicants to reach the brain.
• Ozone: Inhalation of reactive oxygen species. Ozone is a reactive oxidizing agent that can induce oxidative stress and neuroinflammation in the brain.

The cellular mechanisms of neuroinflammation involve astroglia and microglia, the resident innate immune cells in the brain. Astroglia are activated in response to injuries of the CNS, while microglia can become chronically activated by neurotoxic stimuli, leading to the release of pro-inflammatory factors and oxidative stress.

Overall, air pollution can cause neuroinflammation and neurotoxicity, potentially contributing to conditions such as autism and Alzheimer's disease. The aging brain and developing brain may be particularly susceptible to the neurotoxic effects of air pollution.

Air pollution can have adverse effects on the immune system during critical windows of development, such as pregnancy, infancy, and childhood

Pregnancy

A study in Beijing, China, found that women who were in their eighth month of pregnancy during the 2008 Olympics, a time when the city was mandated to lower emissions and improve air quality, delivered babies who were on average 0.8 ounces heavier than those born during the same calendar months in previous years. This suggests that exposure to air pollution during pregnancy can lead to low birth weight.

A study by The Stockholm Environment Institute at the University of York found that nearly three million babies are born prematurely each year due to air pollution, with 18% of all annual preterm births linked to exposure to particulate matter pollution.

A Harvard study revealed that women exposed to high levels of particulate matter pollution during their third trimester were twice as likely to deliver a child with autism, especially if they lived near a highway.

Infancy and Childhood

A study in Durban, South Africa found that infants born from mothers with higher levels of exposure to particulate matter were more likely to be born with low birth weight and small for gestational age, partly because of being born prematurely.

A study in Canada reported an association between exposure to nitrogen dioxide and particulate matter in the second trimester with an increased risk of developing asthma in children.

Mechanisms

The mechanisms by which air pollution affects the immune system are not yet fully understood. However, some studies suggest that air pollution can cause oxidative stress and trigger the release of inflammatory mediators, leading to an inflammatory status characterised by cytokine production and immune cell activation.

Mitigation

To protect the health of children and support sustainable development for future generations, local governments need to prioritise air pollution reduction, and healthcare providers should advise pregnant women about the risks of air pollution during pregnancy.

Air pollution can increase the risk of allergies and asthma

Air Pollution, Allergies, and Asthma

Air pollution is a contamination of the air with harmful substances, including gases and small particles. It can cause and worsen asthma, a condition affecting nearly 28 million people in the United States alone. Certain pollutants are known to disrupt the epithelium, leading to diseases in organ systems with epithelial linings.

Risk Factors

Air pollution can increase the risk of developing asthma. People with existing lung diseases like asthma are especially vulnerable to the harmful effects of air pollution. Other high-risk groups include those with heart disease, those who work or exercise outdoors, pregnant individuals, people living near sources of pollution, and those with lower incomes.

Types of Pollutants

Small airborne particles, found in haze, smoke, soot, and dust, can lead to serious air quality problems. These particles, called "particulate matter" or PM, can get deep into the lungs or even the bloodstream. The smallest particles (PM2.5) are the most dangerous. Examples of PM10 include dust, pollen, and mold, while PM2.5 includes combustion particles, compounds, metals, smoke, and soot emissions.

Ozone, a common air pollutant, is helpful in the upper atmosphere but harmful when found in the air we breathe. Ground-level ozone is associated with respiratory diseases like asthma and chronic obstructive pulmonary disease (COPD). It is particularly common in cities with more cars and the use of fossil fuels.

Nitrogen dioxide (NO2) and sulfur dioxide (SO2) are also harmful gases. NO2 comes from burning fuels and emissions from vehicles and power plants, while SO2 comes from burning fossil fuels, transportation, volcanoes, and industrial processes. Both gases can harm the lungs and lead to health problems.

Health Effects

Air pollution can cause difficulty breathing, decreased lung growth in children, reduced lung function, and adverse birth outcomes. It can also trigger asthma symptoms and lead to an increased need for medication and emergency treatment.

Preventative Measures

On days with high air pollution levels, people with asthma should limit their time outdoors, especially during the late morning to early evening. Staying in a well-ventilated, air-conditioned building can help reduce exposure. Additionally, it is important to avoid exercising or working hard outdoors when air pollution levels are unhealthy.

Indoor Air Pollution

Indoor air pollution can also pose health risks. Sources of indoor pollution include household cleaners, fuel-burning heat sources, smoke from cooking or fireplaces, toxic fumes from new products, attached garages, building and paint products, pesticides, radon, and cosmetics.

To reduce indoor air pollution, it is recommended to remove or reduce allergens, prevent mold growth, increase air flow, and avoid using scented products. Certified asthma and allergy-friendly air cleaners or filters can also be installed.

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