less filtered by ozone layer, so 100 times more intense than UVB (however, less damaging)
penetrates deeply to the dermis
responsible for sun-aging
UVB
(290 - 320 nm)
well-filtered by ozone layer, but more capable of causing damage than UVA
mostly scattered in stratum corneum; may reach papillary dermis
main agent responsible for sun damage and skin cancer
UVC
(200 - 290 nm)
absorbed by ozone layer; does not reach the Earth’s surface
Sun Damage
sunburn
: complex process involving both inflammation and immunomodulation; most common response to UV
sunburn cells
: dyskeratotic and vacuolated keratinocytes (major histologic changes seen)
MED
(minimal erythema dose): min. dose to previously unexposed skin that yields well-demarcated erythema
Langerhan’s cells, keratinocytes, and melanocytes release mediators (histamine, IL-1, TNF-a , etc) in response to UV exposure leading to an immune response, followed by changes in #/activation levels of immune cells in skin
secondary activation of vascular cells and extracellular matrix in the dermis occurs as well
actinic keratosis
pre-malignant hyperkeratotic nodules or plaques; rough, scaling, poorly demarcated
component of sun-aging and may lead to squamous cell carcinogenesis
kerato acanthoma
pre-malignant prominent hyperkeratosis (overactive actinic keratosis); may invade dermis
consists of well-differentiated keratinocytes; a ‘horn’ of keratin may also protrude from the skin
most will involute due to immunologic attack, but not all do, thus leads to cancer
carcinogenesis
UV light produces thymidine dimers; if not repaired, cause DNA replication errors
xeroderma pigmentosum
: dimer repair inoperative Þ highly susceptible to sun damage
p53
: initiates repair, cell-cylce arrest, and possibly apoptosis in the event of DNA damage
mutation in p53 is a common initiator or promotor of carcinogenesis
FAS/FAS ligand
: apoptotic pathway that can be initiated by UVB
basal cell carcinoma tends not to metastasize whereas melanomas are very quick to metastasize
Cell-Mediated Immunosuppression
Antigen presenting cells are intensely affected by UV exposure, leading to UV-induced cell-mediated immunosuppression
Langerhan’s cells
: UV exposure Þ loss of dendricity, number, some surface markers Þ loss of effectiveness
partially, but does not fully explain immunosuppression
Macrophages
: UV exposure leads to:
increased IL-10 (IL-10 is an immunosuppressive cytokine)