As one might predict, there are scant studies of immunotoxic effects specifically in children.

Case study reports suggest that learning disabilities and behavioural and attention problems may be associated with sensitization to environmental irritants in some children.

Immunological Effects

The immune system is the body's defense against infection from foreign agents, but it may also play a role in containing malignant cells and thereby resisting tumour formation and cancer. There is much uncertainty and less is known about the immune system effects from exposure to environmental contaminants in humans by comparison to cancer.

Mammalian immune systems must undergo a series of developmental changes in early life prior to full functionality being established. It has been suggested that there are five discrete immune system developmental events that likely define periods of greatest vulnerability to immunotoxic substances. These are portrayed in the chart below.75,76

As is the case for effects in other body systems, the degree of immunotoxicity will depend on the timing of the exposure with respect to immune system development.

Immunotoxic Effects

Two main immune system effects may be associated with exposure to toxins:

1. Direct damage that causes immune suppression may render the individual more susceptible to infections and cancer; and
2. Indirect response to effects elsewhere - immune sensitization or heightened (sensitized) function may allow for development of allergic or hypersensitivity reactions to antigens.

Evidence for immunotoxicity from environmental exposures comes largely from experimental studies and wildlife observations. The few human studies have come mainly from occupational or accidental exposures (i.e., relatively high-dose exposures), primarily in adults.77 As one might predict, there are scant studies of immunotoxic effects specifically in children.

Apparently the perinatal period represents a time of greatest susceptibility to immunotoxic effects from exposure to environmental substances. Perinatal exposure can produce persistent effects at doses much lower than those necessary to affect adult immune functioning.78

What little evidence does exist has suggested that a number of exposures may cause an immuno-suppressive effect in humans, as shown by changes in antibody levels or immune cell numbers. Curiously, the clinical significance of these alterations has not been uniformly clear, as there are only rare reports of associated increased risk of infections.

Environmental Chemical Sensitivity

The role of the environment and the immune system in the etiology of infections and allergic reactions is well-characterized. However, there is considerable disagreement regarding the environmental and immune system links to the illness known as Environmental or Multiple Chemical Sensitivity (MCS). MCS is a phenomenon that describes individuals (primarily adults) who exhibit a cluster of symptoms, such as headache, breathing difficulties, fatigue, muscle aches and inability to think and function, for which there appears to be no demonstrable clinical basis.

Individuals frequently report symptoms after exposure to what would normally be low levels of chemicals (triggers) and they sometimes recall that their illness began after a distinct episode of over-exposure to some chemical (an initiating event).79 In most cases, the causal associations between exposure and hypersensitivity symptoms are unproven. There has been no consensus on how such syndromes are defined, what the cause of sensitivity is, or the mechanism by which symptoms might be triggered.80

Despite problems with the diagnosis, etiology and treatment of environmental hypersensitivity disorders,81 and recognition of the fact that not all individuals are equally likely to exhibit such responses to environmental stimuli, most clinicians acknowledge that MCS sufferers do experience considerable ill health effects.

There is much less known about environmental hypersensitivity in children. The diagnosis and prevalence among children are not well characterized. Hypersensitive children are known to develop strong reactions to a variety of allergens, such as moulds, house dust mites and tobacco smoke and to have reduced tolerance to synthetic chemicals found in food, air and water. Case study reports suggest that learning disabilities and behavioural and attention problems may be associated with sensitization to environmental irritants in some children.82

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