Protective role of <i>Aspergillus fumigatus</i> melanin against ultraviolet (UV) irradiation and <i>Bjerkandera adusta</i> melanin as a candidate vaccine against systemic candidiasis

Abstract

Melanin protects pigmented cells from physical and biological stresses which are associated with virulence in several important human pathogens, but little is known about the immune response to this ubiquitous biologic compound. Melanin content increased in Aspergillus fumigatus mycelium exposed to ultraviolet for 10 min but gradually decreased after 60 min of UV exposure. So, it can be concluded that melanin protects fungus for survival until 60 min which was obvious after studying conidia and mycelia by transmission electron microscope (TEM). This research hypothesized that melanin produced by a higher fungus, Bjerkandera adusta, is immunogenic against fungal infection. Melanin was purified from melanized fungal hymenium layer and used in mice immunization, then the actively immunized mice were challenged 1 day later with 10⁷ candidal spores. The antibody (Ab) response was evaluated by radio-immunodiffusion diffco-plate of IgM for accurate quantitative measurements of immunoglobulin in biological fluids. Candidasis was detected in mice target organs after the challenge and urea was assayed to detect the degree of kidney damage. The results demonstrate that melanin could be immunogenic; this is indicated through IgM follow-up and its development might suggests that this amorphous insoluble polymer can stimulate the immune system against the latter challenge, thus reducing the degree of infection. This was observed through the reduction of candidiasis and the enhancement of kidney function.

Key words: Melanin, ultraviolet (UV) irradiation, active immunization.