How UV-radiation affect the immune system

How UV-radiation affect the immune system
7. What are the effects of solar UV radiation
exposure on the human eye and how can the eye be
protected?
The effects of UV radiation on the eye may be acute (occurring
often after a short, intense exposure usually after a latent period of
several hours) or long-term after an acute exposure. There are also
long-term effects following chronic exposure of the eye to levels of
UV radiation below those required for the acute effects.
The commonest acute effect, photokeratitis (snow blindness)
leaves few or no permanent effects, whereas cataract due to chronic
exposure is irreversible and ultimately leads to blindness.
Avoidance of exposure to the sun is an effective but impractical
means of avoiding exposure of the eyes to UV radiation. Because
of this, additional protection is frequently needed under conditions
of high ambient UV irradiation and/or reflective surfaces.
Appropriate glass and plastic lenses absorb all UV-B and
much of the incident UV-A. Even clear spectacle lenses provide
protection from UV-B. However, in the case of non-wrap
around spectacles, ambient UV radiation may enter the eye
from the side. This effect can be exacerbated by tinted sunglass
lenses which encourage a wider opening of the eye and pupil.
UV-radiation-blocking soft contact lenses, that cover the entire
cornea, effectively shield the cornea and ocular lens against UV
radiation incident from all angles (Fig. 10). They offer a UV
protection alternative in those situations where the wearing of
sunglasses is not practical or convenient.
Fig. 10 Soft UV radiation-absorbing contact lens covering the entire
cornea. Photographed in blue light to show the contact lens.
Q8. What are the effects of solar UV-B exposure on
the human skin and how can the skin be protected?
Acute exposure of the skin to solar UV radiation causes sunburn
and, in the long-term, skin cancer.
The amount of UV radiation required to produce sunburn
depends on the absorption in the superficial layers (varying with
the amount of pigment) of the skin and on other genetic factors.
The efficacy with which sunlight produces sunburn depends on
the amount of UV-B radiation present; more UV-B is present at
high altitudes and more is present in noontime sun than at earlier
of later hours. Chronic exposure of the skin to UV radiation
causes photo-ageing (including wrinkling, thinning, and loss of
elasticity); however, UV-A may be more important than UV-B in
causing these latter changes.
Basal and squamous cell carcinomas occur most often and with
high frequency in fair-skinned individuals living in sunny climates.
Fortunately, most of these skin cancers are readily treated and
rarely fatal. Cutaneous melanoma (Fig. 11) is considerably more
dangerous, but occurs with much lower frequency than the other
types of skin cancer. The relationship between melanoma and
UV-B radiation is not well understood, but exposure in early life
seems to be an important factor in its development. Dark skinned
persons have natural protection in their skin against sunlight.
Although melanoma does occur in darker skinned persons, such
cancers are often not related to sun exposure.
Fig. 11 Early cutaneous melanoma.
Methods of decreasing sun exposure of the skin include
remaining indoors during the peak UV-B hours around midday
and seeking shade at other times. Broad brimmed hats, sunglasses
and full-body clothing that reduce the area of exposed skin are
also effective.
Sunscreens are designed to protect against sunburn and can be
highly effective. There is evidence that they reduce the incidence
of squamous cell carcinoma and precancerous lesions in the skin.
Obtaining a suntan will not necessarily prevent UV-B induced skin
cancer and the UV radiation exposure needed to acquire the tan
adds to the skin cancer risk.
Q9. How does UV-radiation affect the immune
system?
The immune system can be altered by UV irradiation, leading to
diminished immune responses to infectious agents and skin cancers.
Some cells of the immune system, called antigen-presenting
cells, reside in the skin. Their function is to survey the skin for
foreign challenges, such as invading microorganisms or tumour
proteins. They capture any molecules they find and carry them
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to the nearest lymph node where the active immune response
is initiated. Exposing the skin to UV-B radiation causes several
changes—one leads to a change in the antigen-presenting cells
so that the immune response may induce suppression (Fig. 12).
Another is to stimulate the production of a particular range of
immune mediators in the skin that also favour suppressing imm