[The cow, the boy and the lymph node--immunological principles for vaccines].

Vaccines stimulate the immune system by activating professional antigenpresenting cells, such as dendritic cells. Dendritic cells express a number of pattern recognition receptors (PRR) on their surface, receptors that recognize structures on viruses and bacteria. These receptors stimulate maturation of dendritic cells that thereafter migrate to regional lymph nodes where they present vaccine antigens to T-cells. PRR- ligands of the vaccine are decisive for the efficacy of the immune response. This article discusses cellular principles and mechanisms for vaccine responses; including antigen processing and presentation, T-cell circulation, Th1-, Th2- and CTL T-cell responses and T-B cell cooperation, as well as primary and secondary T and B cell responses and lymphocyte recirculation and homing.