Dendritic cells (DC) belong to the group of antigen-presenting cells (APC). One of the first functions discovered of the dendritic cells was the very important role they play in the activation of specific immune responses against pathogens.
Because of this function, the dendritic cells are often called natures adjuvant. In recent years, through increasing understanding of the role of the dendritic cells in the immune system, new areas of clinical application were discovered and conducted.
One example may be the improved immune response in vaccination of non-responders.
Very recently, the possible role of the dendritic cells in the biological immune response against malignancies (solid tumors) was discovered and clinically investigated.

The dendritic cells form a complex network of APC within the organism. [2] In early stages of differentiation, in skin and mucosa, the dendritic cells have been described as so-called Cells of Langerhans (CL).
CL function as perceivers and incorporators of, for instance, viral and bacterial antigens, and toxins.
After perception of an antigen, CL are activated by local inflammatory signals (through the production of certain cytokines, including IL-2 and Il-6), and start wandering mainly through the lymphatic system, and to a certain degree through the blood flow, to the secondary lymph nodes.
Here, as fully differentiated, so-called inter-digitating dendritic cells (IDC), they settle in the T-cell areas and begin to activate T-cells antigen-specifically.

Thus, the function of the dendritic cells is the transportation of antigen from the location of infection to the secondary lymph nodes, where the specific immune response against the antigens and toxins is orchestrated.
Through this transportation of antigens by dendritic cells to the lymph nodes, it is made easier for T-cells to come into contact with the antigens, as non-activated T-cells circulate through the peripheral lymph system several times during a 24-hour period.
After being activated by DC, T-cells change their wandering pattern, and become effector cells at the location of infection. As cytotoxic T-cells, they destroy infected cells in the body, and, interestingly, also tumor cells.
As T-helper cells of the TH-1 type, they stimulate macrophages in their phagocytic and bactericide activities, by producing inflammatory mediators, to eradicate intra-cellular pathogens, like tuberculosis bacteria. As TH-2 cells, they support the humoral immune response by activating the anti-body producing B-cells.

APC play an important role in recruiting antigen-specific T-cells to adapt properly the immune response. Usually, T-cells by themselves do not recognize antigens. APC have to prepare this recognition process.
This means that within the APC, the (specific) antigen is dissected into much smaller peptides, and bound to the major histiocompatibility complex class I (MHC-I). Afterwards, this MHC-I is presented at the surface of the cell membrane.
Only then, T-cells are able to perceive the complex between the MHC-I molecule and the antigen peptide. This leads to the activation of the resting T-cells. In the periphery of the body CL are specialized in antigen recognition and antigen processing, but still have little potential for activation of resting T-cells.
After their wandering to the secondary lymph nodes, and maturation into IDC, the process is reversed. Now, the IDC have lost the ability to recognize and process the antigen almost completely. Instead, IDC, after having incorporated and presented the antigen on the cell surface in its CL stage, are now able to activate resting T-cells.
Thus, within the lymph node, IDC guarantee that a most accurate picture is transmitted to the T-cells about the nature and the characteristics of the infection in the periphery. The specific capability of the dendritic cells to activate naïve T-cells can be used in immune therapies, like in cancer.

The purpose of our clinical and research activities will be, to sensitize DC for tumor-specific antigens. Thus, returned to the cancer patient through an infusion (as a cellular vaccine), in this way specifically activated T-cells of the patient will be able to eliminate tumor cells and pathogens, including chronic viral infections, like hepatitis C, human papilloma virus (HPV) in persistent cervix dysplasia, and HIV.
Recently, it was found that pre-loaded DC with human immunodeficiency virus type 1 (HIV-1) provoked strong responses from CD8+ T-lymphocytes of late-stage HIV-1 infected individuals. These responses were enhanced under application of gamma-interferon and interleukin-2, strongly suggesting that DC of HIV-1 positives can be engineered to evoke a stronger anti-HIV-1 CD8+ T-lymphocyte reactivity as a strategy to augment anti-retroviral therapy.

The rat dendritic cell is interacting with what is probably a helper T cell. Through such interactions, dendritic cells teach the immune system what it should attack. Cells maturated in the laboratory, are beeing used in cancer vaccines.

References:
1. Steinmann RM: The dendritic cell system and its role in immunogenicity.Ann Rev. Immunol. (1991) 9:271-296
2. Fan Z, Huan XL, Borowski L, Mellors JW, Rinaldo CR: Restoration of anti-human immunodeficiency virus type 1 (HIV-1) responses in CD8+ T cells from late-stage patients on prolonged antiretroviral therapy by stimulation in vitro with HIV-1 protein-loaded dendritic cells. J Virol (2001) May, 75(9): 4413-4419