Skin Photobiology and Photo immunology ppt Dermatological background

1. Anand

5. • UV Light 200-400 nm wavelength
• 3 Types:- UVA, UVB & UVC
• 90% -UVA
• 10%-UVB
• UVC –Don’t reach earth surface

8. UV C
• 200 - 290 nm
• <290 nm are absorbed by ozone
• Strongly absorbed by DNA and therefore can be
lethal to viable cells of the epidermis
• Care to avoid exposure of eyes & skin to UVC
radiation
• Bactericidal:-Used for air & water purification
• a.k.a Germicidal radiation

9. UVB
• 290 to 320 nm is mid-UV /sunburn spectrum
• UVB -5% of the UV &0.5% of total radiation
• Ordinary window glass blocks UVB
• Most sunscreens efficiently reflect or absorb
these wavelengths, and SPF is primarily based
on testing against this waveband

10. • And more effectively causes DNA damage &
photocarcinogenesis.
• NB-UVB(311 nm) & Excimer laser (308 nm) are
used to treat psoriasis

11. UVA
• UVA I (340–400 nm) & UVA II (320–340 nm)
• UVA II more damaging to unsensitized skin
• SPF≥ 45 some UVA protection
• UVA causes photoageing & carcinogenesis

12. VL , Xrays ,Gamma rays…
• The visible spectrum (400–760 nm) is defined
by the wavelengths that are perceived as color
by the retina
X-ray and γ rays :-
• In RT of tumors- ionize(Remove electrons) of
water molecules & produce ROS that damage
DNA

13. Infrared
IR-A (760–1,440 nm)
IR-B (1,440–3,000 nm)
IR-C (3,000 nm–1 mm)
• IR-A causes skin damage
• Recent studies -IR-A wavelengths can also be
therapeutic
• Whereas IR-B and IR-C are felt as heat.

14. Uses of EM Radiations
• VL– in Blue-light ALA–photodynamic therapy
• Several lasers
• UVB Phototherapy
• PUVA Photochemotherapy

15. • UV and/or visible radiation also from
Fluorescent lights
Incandescent bulbs
Photocopy machines &
Phototherapy lamps

16. Artificial Sources
• Incandescent Lamps
• Fluoroscent lamps
• Arc lamps
• Woods lamp
• Halide lamps

17. INCANDESCENT SOURCES
a)Conventional electric light bulbs- VR & IR
• An electric current heats the filament &
emits -VR & IR
b)Tungsten-halogen(flood lamps)- UVA & VR
c) Quartz iodide lamps -UVA & UVB

18. ARC SOURCES
• Xenon lamps,medium- and high-pressure
mercurylamps, fluorescent lamps & halide lamps
• In arc lamps, electrons are driven through a gas
by a potential difference between two electrodes.
• The gaseous molecules are ionized and
subsequently release EM radiation.
• Xenon arc lamps - UV & visible radiation
• Used as solar simulator

19. Fluorescent lamps
• Source of UVB & UVA lamps
• Are modified low-pressure mercury arc lamps.
• The inner surface of the glass tube is coated
with a phosphor, which absorbs the 254-nm
radiation and reemits the energy at longer
wavelengths.
• The chemical composition of the phosphor
determines which wavelengths are reemitted.

20. • Emission peak at 311 nm (Philips TL01)
• Used in phototherapy
• Rx-Psoriasis,Vitiligo, AtopicDermatitis & PMLE

21. • Hot quartz Lamps – medium & high-pressure
mercury lamps - sources of UVB
• Wood’s lamps- low-pressure, UVA emitting
fluorescent lamps with a UVA-transmitting,
visible-absorbing glass envelope

22. Halide Lamps
• Halide lamps emit a high-intensity continuum
UVB along with UVA range
• Mainly as a UVB source

23. LASERS
• Monochromatic (single wavelength) radiation
• Different lasers emit UV, visible Or infrared
• Either continuous or pulsed source

24. • E …….Joules
• Power(W)….. J/sec
• Irradiance….. W/cm2
• Fluence/Dose of light…..Energy
cm2

25. Spectral irradiance
• The irradiance delivered by a source as a
function of wavelength is called the spectral
irradiance and is expressed as units of
irradiance per nanometer [(W/ cm2)/nm]
• A spectroradiometer is used to measure the
spectral irradiance of a light source

26. • More wavelength means more penetration
• UVA,VL & IR will reach upto S/c tissue
• UVB upto mid dermis only
• 10% of 300-nm & 50% of 350-nm reaches DEJ
• More energy – More erythema
• More energy– More scattering
• UVB scattered more easily than UVA

27. • 5%-10% of incident light -reflected by
S.corneum.
• Reflected,Scattered
• Absorbed by chromophores in various layers

28. • Specular reflectance is relatively constant for all
visible wavelengths and accounts for the
surface appearance of skin
• “Glossy” if the surface is smooth, wet, or oily.
• “Rough” if irregular.
• Moisturizers applied to the skin make the skin
look shiny

29. Application
• Skin with scales-as in psoriasis- scatters more
• During phototherapy-Apply emmolients
• Allows more of the effective wavelengths to
penetrate into the viable tissue.

30. • Melanin, which absorbs relatively uniformly
over the visible wavelengths in epidermis will
decrease the remittance
• The greater overall melanin content the lesser
light will be remitted back to the observer.
• Hemoglobin within the dermis absorbs mainly
blue spectrum and remits red
• This explains melasma & vitiligo discolouration

32. Vitamin D
• Chick independently observed that sunlight
would cure rickets just as well as cod-liver oil
• Hess -cholesterol in skin is activated by UV-
irradiation and rendered antirachitic
• Steps in the vitamin D pathway- elucidated by
Velluz

33. • Vitamin D- Promotes
• 1)Absorption of Ca & Phosphorus from the
intestines
• 2)Reabsorption of calcium in the kidney
• Vitamin D – Inhibits
• 1)Proliferation of T-cells &
• 2)Maturation of dendritic cells
• 3)Keratinocyte function.
• Rickets in children and Osteomalacia in adults
• Contributes to osteoporosis.

34. BIOCHEMICAL PATHWAY
• Provitamin D3 (7-dehydrocholesterol)
• Previtamin D3
• Isomerizes to vitamin D3, entering the circulation on a
binding protein
• Joins with dietary D2 (ergocalciferol) & D3
(cholecalciferol) absorbed from the gut
• Liver- passive hydroxylation -25-hydroxyvitamin D3
(calcidiol)
• Kidneys- 1,25-hydroxyvitamin D3 (calcitriol)
• Bound to a carrier- vitamin D-binding & transported
to various target organs.

36. • Most effective production in 295 nm -315 nm,
(most responsible for photocarcinogenesis)
• 10–15 min ,Twice in a week
• Face, arms, hands, or back without sunscreen
• Vitamin D production decreases >70 yrs
• More melanin in skin = More exposure

37. • We make 10,000–25,000 IU of vitamin D upon
at one MED exposure
• Within 20 min of sun exposure in fair-skinned
individuals (1–3 hrs for pigmented skin)
• Sun protection recommendations may
interfere with vitamin D production

38. • Low vitamin D levels & Parkinson’s disease
• Excess Vit-D with-DM ,Multiple sclerosis , HTN
M.I, affective disorder,chronic pain, PAD,
Memory loss
• Preventing colorectal Ca , breast & prostate Ca

39. Vit D
• Optimal level in blood 30ng/mL
• 1,000 IU daily
10,000 IU weekly
50,000 IU monthly
• Levels < 15 ng/ml – prescribe 50,000 IU
Vitamin D weekly for 8 weeks and then
switches to standard maintenance doses

40. • Persistently low levels, despite several
attempts at correction …..Malabsorption &
referral to a gastroenterologist
• A trial of UVB light therapy may be considered
to improve vitamin D status
• High body mass index (BMI) with Vit D
deficiency require higher doses

42. Photoproducts
Stimulate cellular signal transduction pathways
leading to Biochemical changes
Proliferation, Secretion of cytokines, and Apoptosis
Acute skin responses.

43. Absorption Spectra
• A chromophore will take up only a specific
wavelength of photon

44. Absorption maxima of various
Chromophores
• Absorption maxima means the wavelength which
has the greatest probability of absorption
• Purines & Pyrimidines- 260 nm
• Amino acids-290 nm
• Hemoglobin -410
• Bilirubin-450
• Melanin –UV& VL ( No distinct value)
• Psoralens -UVB

46. Ground state
Singlet excited state (a few nanoseconds)
Photoproducts
Internal conversion
Fluorescence
Intersystem crossing
Triplet excited state
Phosphorescence
Intersystem crossing

48. Applications
• The heat generated by internal conversion is
responsible for the effects of pulsed lasers

51. • The photoproduct molecule produced by
rearrangement of the bonds in the
chromophore
Eg:- pyrimidine dimer (CPD) in DNA

52. • The term quantum yield indicates the
likelihood that one of these processes occurs

53. • Excited state chromophore transfers its
energy to O2 ROS
• These ROS initiates inflammation in sunburn &
drug phototoxicity.

54. • Cell Membranes
• ROS Phospho Lipase A2
•
• Arachidonic Acid
• cox lox
•
• Eicosanoids

55. • Photosensitization:-
• Tetracyclines,FQ, Psoralens & Dyes
• Delayed erythema & inflammation
• ROS will oxidize Lipids in membranes
Amino acids in proteins &
Guanine in nucleic acids
• The oxidized products will produce erythema
• Topical antioxidants can modulate it.

56. • PG &NO appear to be the major mediators
Eg:- PGE2, PGF2α & PGE3 levels increased
• Inhibiting cox with indomethacin used for
UVB induced erythema

57. • UV induced signs of inflammation
1. Erythema:- Increased blood flow
2. Temperature:-Increased
3. Swelling (increased vaso permeabilty) &
4. Pain (released mediators)

58. UVA UVB
Immediate erythema, Deep red Starts after 3-5 hrs, Bright red
Increases melanin production and transfer of
melanosomes to keratinocytes
Increases number and activity of
melanocytes
Less protective from sunburns More protective(Increases ‘t’ of s.corneum)
Not much effect in Vit D synthesis Major role
Less photo ageing and carcinogenesis More chance
UVA MED in fair skin is 30–75 J/cm2 UVB MED for fair skin is about 30 mJ/cm2

59. HISTOLOGY- UVB
• “sunburn cells,” (apoptotic
keratinocytes)appear in the
epidermis at 30 min after a
3 MED exposure.
• Intercellular edema &
Dermal changes persist to
72 hrs
• Endothelial cell swelling,
perivenular edema &
degranulated mast cells
• Neutrophils influx peaks at
14 hrs.
UVA -HISTOLOGY
“Sunburn cells” :-Not apparent
The major histological changes
after UVA occur in the dermis
•Epidermal intercellular edema
48hrs
• LCs decreased over 48 hours
•A lymphocytic infiltrate was also
apparent throughout the dermis
•In the dermis, Neutrophils present
for at least 48 hours

60. • DNA is one of the important chromophores
that initiate pathways leading to UV-induced
inflammation
• X. pigmentosum patients prolonged UVB
induced erythema that can be reduced by
treatment with a DNA repair enzyme

61. Sunburn
• Production of inflammatory mediators &
cytokines causes sunburn response
• The time in the sun required to produce
sunburn is strongly influenced by many factors
including skin pigmentation, season,
geographical location, cloud cover and time of
day.

63. SLIP, SLOP, SLAP

65. Photo immunology
• UV light induces Cancer via
1) DNA damage
2) Mutation
3)Immunosuppression

66. • Uv induced tumors have a highly antigenic
phenotype
• Treatment with low doses of UVB, led to failure of
tumor rejection(Due to immunosuppression)
• Various researches been done in this field
• Those are very complex & the results are
contradictory

67. Immunosuppression
• 2 types:
• (1) local immunosuppression in which the
• immune response to antigens applied at the
irradiated site is impaired
• (2) systemic immunosuppression in which the
immune response to antigens applied to
unexposed sites is impaired
• Mice with the genetic loci for Lps & Tnf are
more susceptible to UVB-induced
immunosuppression

69. Actions of UV light
1. DNA is a chromophore for UVB radiation
produces CPD- -causes UV-induced
immunosuppression
2. CPD in Langerhan cells & immunosuppression
3. PAF receptor activation causes
immunosuppression
4. Aberrant receptor clustering-
Immunosuppression
5. Changes in cell membrane
6. UCA mediated immunosuppression

70. 1)Pyrimidine dimers(CPD)
• DNA is the direct target for UVB radiation
• And produces Pyrimidine dimers(CPD)
• This will cause UV induced immunosuppression

71. 2) CPD s in LC
• UVB CPDs in antigen-presenting cells (APCs)
and impair their antigen presenting capacity.
• The damage persists for several days, and the
damaged cells migrate from the skin to lymph
nodes
• Topical application of photolyase-containing
liposomes to UVB-exposed sites prevents
UVB-induced immunosuppression

72. 3) PAF Receptor activation
• UVB radiation can lead to lipid peroxidation of
cell membrane lipids. (By ROS)
• Phosphatidylcholine, can be oxidized to
(PAF) “like” lipids that bind to PAF receptors
• PAF receptor activation stimulates a variety of
downstream effects, including the synthesis of
immunosuppressive cytokines (ie IL-10)
• Resulting in immunosuppression

73. 4) Aberrant receptor clustering
• UVB exposure leads to clustering &
internalization of cell surface receptors for EGF,
TNF &IL-1 in the absence of the respective ligands
• Such aberrant receptor clustering may subvert
signaling pathways normally used by growth
factors and cytokines, eventually contributing
to the immunological response mainly
immunosuppression

74. 5) Changes in cell membrane
• Cytoplasmic tryptophan is a UVB chromophore
• The resulting tryptophan photoproduct bind to
arylhydrocarbon receptor
(AhR)= c-src + Hsp90
• AhR complex dissociates and the Hsp 90
translocates into the nucleus whereas c-src
translocates to the cell membrane
• C-SRC causes various changes in cell membrane

75. 6) UCA Mediated
• An extracellular chromophore that mediates
UVB induced immunosuppression is
UCA(Urocanic acid)

77. CELLULAR EVENTS INVOLVED IN
PHOTOIMMUNOSUPPRESSION
• UVB radiation of keratinocytes induces
IL-1, IL-6, IL-8, TNF-α & PGE2
• TNF-α &IL-10 - immunosuppressive cytokines
• UVB Stimulates Th2 cells & T-suppressor cells &
Suppresses Th 1 cells

78. IL -10
• The key immunosuppressor cytokine
• IL-10 is a - Th2 cytokine
• Impairs Th1 cytokines production
• Thus impairs Th1 mediated cellular reactions
• IL-10 inhibits the antigen-presenting capacity
of LCs
• PAF and its receptor enhance its production

79. • IL-12 can reverse the IL-10 production
• IL-12 can restore UV-impaired CHS
• IL-12 -enhance the repair of UVB -induced DNA
photoproducts

80. Langerhan cell action
• LCs, 2%–5% of epidermal cells
• DC subset which originates from bone marrow
precursors
• Ingest antigen in the skin, but lack costimulatory
capacity
• After antigen uptake, LCs migrate to the DLN
• At l.node, LC s will express high levels of MHC
molecules & costimulatory molecules -B7.1,B7.2 &
ICAM1
• UV Light Antigen uptake ,MHC II & ICAM-1

81. • UV radiation causes disappearance of LC from
irradiated sites
• UV exposure results in reduced surface
expression of costimulatory molecules B7.1,
B7.2 & ICAM-1

82. • UVB-irradiated LCs activate preferentially
CD4+ Th2 cells
• UVB induced hapten-specific tolerance -i.e.
resensitization with the same hapten at later
time points

83. • CD8+ T cells - important mediators of UVB-
induced immunosuppression
• UV-exposed mice are capable to suppress CHS
by producing IL-10
• In addition, T cells that express (CTLA)-4 on
their surface also causes immunosuppression
• CTLA-4 is an important molecule in immune
regulation in UVB induced immunosuppression

84. ULTRAVIOLET RADIATION EFFECTS
ON INNATE IMMUNITY
• Suppresses adaptive immune response &
Promotes Innate immunity
• UV radiation will induce innate immune response
by increasing the production of the antimicrobial
peptides, human β-defensin (HBD)-2, -3,
ribonuclease 7 in skin
• This may explain why T-cell-mediated immune
reactions are suppressed on UV exposure but not
host defense reactions against bacterial attacks.

85. CONCLUDING REMARKS
• Photoimmunosuppression-A protective method
Modern approaches to prevent immunosuppression
• Broad-spectrum UV filters,
• Liposomally encapsulated DNA repair enzymes
• Taurine uptake
• IL-12
• Antioxidants & Osmolytes

87. Acknowledgement
Thomas.B.Fitzpatrick(1919-2003)