Urticaria (Hives)
Type 1 rxn of skin
Eczema
Allergens taken up by Langerhans cells, presented to naive T cells that develop memory. On re-exposure, T cells proliferate and home to skin where their cytokines produce the damage.
Erythema Multiforme
Type IV cytotoxic rxn. CD 8 T lymphs become sensitized to an unknown antigen within epithelium and kill keratinocytes
Psoriasis
- HLA related TH1 cell mediated rxn to an unknown antigen
- TNF is the major mediator
Lichen Planus
- Type IV cytotoxic rxn to an unknown antigen
- Causes slowed epithelial turnover = orthokeratosis
Discoid Lupus Erythematosus
Type III rxn. Deposition of immune complexes and complement in bm zone.
Pemphigus
- Type II rxn (antibody mediated cellular dysfunction)
- IgG or M forms against intracellular cement (desmoglein 1 and 3) and deposits around desmosomes but not hemidesmosomes causing cell bridges to fall apart.
Bullous Pemphigoid
IgG directed against hemidesmosomes
Dermatitis Herpetiformis
Certain HLA types predispose to antibodies produced against gliadin (in gluten) which cross react with reticulin, which anchors bm to papillary dermis.
Verruca Vulgaris
Caused by HPV 2, 4, 6, 40
Squamous Cell Carcinoma
- Field Theory - sun effects a large area causing transformation of multiple cells rather than a clone
- Other causes: arsenic, radiation, burn scars
Keratoacanthoma
- Unknown etiology
- Arises from hair follicle epithelium
- It shows p53 mutations and may represent a SCCA that regresses because it is destroyed by host tissue or cannot fully establish independent growth
Basal Cell Carcinoma
Sun-induced somatic mutation of both alleles of a tumor suppressor gene.
Basal Cell Nevus Sx
Genetic mutation of 1 allele of a suppressor gene requiring a 2nd hit to inactivate the other allele
