Papular urticaria is a chronic allergic disease caused by exposure to ectoparasites. It presents as a hypersensitive reaction with skin lesions (wheals, papules, vesicles and scaba), often leaving residual hypopigmentation or hyperpigmentation and leading to intense pruritus, secondary infection and scarring. Diagnosis of papular urticaria is clinical. The current lack of specific laboratory diagnosis, effective and preventive therapeutic tools may be explained, at least in part, by a poor understanding of the immune mechanism involved in the disease's pathophysiology.
Aim of the work: This study was aiming at characterizing the immune response through detecting IgG and IgE against flea (Pulex irritans), mosquito (Aedes aegypti) and house–dust mite antigens in patient's serum by ELISA and immuneohistopathological examination of different skin lesions.
SUBJECTS AND METHODS: Thirty eight patients with papular urticaria (17males and 21 females) were included in this study. All patients were subjected to prick skin test using antigens from mosquito, mites and fleas; ELISA test to detect antibodies against mosquito, mites and flea antigens and skin biopsy.
Results : The results of skin prick tests performed on the patients were negative in 27 cases, As regard IgG level in serum of the patients, it was positive for flea antigens in 25 cases (65.8%); for mosquito antigens in 35 cases (92.1%) and for house-dust mite antigens in 23cases (60.5%). While IgE level in serum of the patients was positive for flea antigens in 36 cases (94.7%); for mosquito antigens in 23 cases (60.5%) and for house-dust mite antigens in 25 cases (65.8%). As regard the distribution of inflammatory cellular infiltrate according to skin biopsy of the lesions among the studied groups there were a predominance of lymphocytes in the vesicles (48%) more than papules and wheals. Eosinophils were more predominant in papules and wheals (54.6% & 57.4%) than vesicles (30%)
CONCLUSION: Contact with animals as dogs and cats or birds has an important role in the etiology of PU. Skin prick test is not so much helpful in determining the causative allergen of PU especially when crude antigens are used. Indirect ELISA technique is a valuable test in diagnosis of papular urticaria. Histopathological changes in papular urticaria denote that the pathogenesis of PU has more than one mechanism including type I hypersensitivity due to presence of abundant eosinophils and type IV cell mediated immunity due to presence of abundant lymphocytes, histiocytes andCD45RO+ cells.
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