The functional variety of dendritic cells (DC) depends greatly on the stage of their development. There can be distinguished: progenitor DC of bone marrow, precursor DC of blood, lymph and lymphoid tissues, and resting DC that are found in tissues and possess a capability of endocytosis, pinocytosis and phagocytosis, which makes it possible to catch antigens (among others, via Toll-like receptors). After contact with an antigen, mature DC initiate an immune response by means of co-stimulating molecules. The enhanced expression of MHC molecules, chemokine receptors (CCR4 and CCR7) as well as co-stimulating molecules (CD40, CD80, CD83, CD86), enabling migration and presentation of antigen particles by mature DC, is observed after resting DC absorb an antigen. Activated DC secrete cytokines (TNF, IL-1, IL-2, IL-6, IL-8, IL-12) and chemokines derived from macrophages that attract T cells and promote the survival of DC via inhibition of their apoptosis. Dendritic cells are activated to mature and secrete cytokines both directly and indirectly by Helicobacter pylori.