Immunological memory has two components (the central one and the peripheral one, which
lasts longer), two branches (cellular and seric) and three functional specialisations of the
lymphocytes: Th1, which produce IL-2 and gamma-interferon and control the cellular response;
Th2, which produce IL-4 and IL-5 and control the seric response, and T-regulating,
which produce IL-5 and control both cellular and seric response. Our knowledge of the effects
on the immunological memory and on the immumological balance of both the dosage
of immunising antigens and the age of immunisation is still incomplete.