How can the immune memory lead to the efficacy of vaccines and also produce allergies?
Vaccines are controlled inoculations of fragments of infectious agents or of inactive infectious agents to induce the primary immune response, the formation of specific memory B lymphocytes against the antigen. Therefore the organism produces immunoglobulins and becomes prepared to destroy antigens when exposed to new infections by those agents. In allergies the humoral immune system is sensitized (makes antibodies and specific memory B lymphocytes) against some common environmental substances wrongly recognized as antigens. For example, pollen-derived substances, dust particles, compounds present in foods or in medicines, etc. may be recognized as antigens triggering the primary response and creating an immune memory against them that then become causes of allergy. The more the individual is exposed to those substances the more intense is the immune reaction. The IgE antibodies that cause allergy bind to receptors of leukocytes called mastocytes whose cytoplasm is full of histamine granules. The antibody- mastocyte bond causes these cells to release a great amount of histamine in the circulation, stimulating inflammation and generating the allergic symptoms and signs. For this reason allergy is treated with antihistamines, drugs that block the histaminic reaction. Exacerbated allergic reactions, for example, in hypersensitivity to some medicines like penicillin and sulfas, may cause anaphylactic shock, a severe clinical condition that sometimes leads to death.
