Immunopathology of psoriasis: a comparison with other parakeratotic lesions.

Characteristic in vivo binding of IgG and C3 to the stratum corneum of psoriatic lesions has been implicated as a significant event in the pathogenesis of the disease. Immunofluorescent findings of psoriatic lesions are compared with other parakeratotic and nonparakeratotic lesions. Parakeratotic lesions studied include verrucae vulgares in patients with psoriasis, verrucae vulgares in patients without psoriasis, actinic keratoses and lichen simplex chronicus. Psoriatic lesions and other parakeratotic lesions demonstrate similar immunopathological phenomena within the involved stratum corneum: (1) A high percentage of the lesions stain positively with one or more of the immunoglobulins (IgG, IgM and IgA). (2) No predominance of any immunoglobulin class is found. (3) The predominant sites of immunoglobulin deposition are within the regions of parakeratosis. (4) C3 deposition is found in a high percentage of the lesions and is present at the sites of immunoglobulin binding. By contrast only a small percentage of nonparakeratotic lesions display stratum corneum fluorescence. These data are consistent with macromolecular leakage through the lesional microvasculature and high affinity binding of immunoglobulins by parakeratotic stratum corneum. Similar immunofluorescent findings in psoriatic lesions and nonpsoriatic parakeratotic lesions suggest that immunoglobulin binding in psoriatic lesional stratum corneum is not a significant event in the pathogenesis of psoriatic lesions.