Tamarind Inhibits Solar-Simulated Ultraviolet Radiation-Induced Suppression of Recall Responses in Humans

To determine whether topically applied biologically active drugs can be used to protect the human immune system from sunlight, we studied the effect of tamarind xyloglucan polysaccharide, a natural and common fruit constituent, on solar-simulated, ultraviolet radiation-induced local immunosuppression and erythema in humans. Immunosuppression was studied in humans using a nickel contact hypersensitivity recall model. Ultraviolet dose responses were generated to determine the extent to which tamarind affected the immune response in a group of 15 volunteers. The subsequent nickel-induced erythema was quantitated using a reflectance spectrometer. 0.1 μgml-1 of topical tamarind polysaccharide reduced ultraviolet radiation-induced immunosuppression. Frozen sections of biopsies taken were analysed by immunohistochemistry. Tamarind inhibited ultraviolet radiation-induced CD11c+ dendritic cell loss from the epidermis. The ultraviolet doses used in this study did not alter the number of Mac387+ macrophages or NP57+ neutrophils infiltrating the skin. Low dose xyloglucan polysaccharide from tamarind protected from immunosuppression in humans, possibly by reducing ultraviolet radiation-induced loss of dendritic cells, demonstrating that these types of drugs may be useful adjuncts to sunscreens for protection from skin cancer.