The origin and role of the Langerhans cell are considered in the immune response of the organism, as well as in a number of human diseases. It is noted that the antigen-presenting function of this macrophage suffers when taking glucocorticosteroid preparations, at AIDS and large doses of ultraviolet radiation. Therefore, the investigation of the effect of UV-irradiated blood reinfusion on the Langerhans cell will help to determine the possibilities of UV-irradiated blood therapy in treating a wide range of diseases, including AIDS, in the transplantation of organs and tissues. 163 refs.; 2 figs.