Q. How can the immune memory lead to the efficacy of vaccines and also produce allergies?

Vaccines are controlled inoculations of fragments of inactive infectious agents or of infectious agents to induce the primary immune response the formation of specific memory B lymphocytes against the antigen. consequently 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 specific memory B lymphocytes and antibodies) against some common environmental substances wrongly recognized as antigens. For instance, dust particles, pollen-derived substances, compounds present in medicines or in foods, and so on. may be recognized as antigens triggering the creating and primary response an immune memory against them that then become causes of allergy and 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 and the antibody-mastocyte bond causes these cells to release a great amount of histamine in the circulation, generating the allergic symptoms and signs and stimulating inflammation. For this reason allergy is treated with antihistamines drugs that block the histaminic reaction. Exacerbated allergic reactions, for instance, in hypersensitivity to some medicines like sulfas and penicillin, may cause anaphylactic shock a severe clinical condition that sometimes leads to death.