Immunomodulators are substances that help adjust the functioning of the immune system. When it is necessary to increase its efficiency so that the body can more easily overcome an infection or virus, immunostimulants are used. In some cases (for example, during organ transplantation or during exacerbation of autoimmune diseases), the activity of the immune system, on the contrary, needs to be reduced. Immunosuppressants are used for this purpose.