T cells

T-cells are white blood cells that are the part of the immune system. T-cells develop from the precursors in the thymus. These precursors migrate from the hematopoietic tissues (mainly from the bone narrow) during the prenatal development.

In the thymus occures the selection of the immature T-cells. Reticular epithelial cells present antigenes to the immature T-cells. The survival of the T-cell depends on its ability to distinguish MHC of the own body. Non-reacting or excessively agressive cells are destroyed (about 95 % of them). Other cells enter the blood. Blood transfers them to the secondary lymphoid organs, where they meet their specific antigens. This leads to their activation and subsequent imflammation development.

Specificity of the T-cells is determined by the development of their TcR (T-cell receptors). They're not enough for the lymphocyte activation (signal transmission) though, in this case indispensable is the membrane complex of the TcR and CD-3.

After the end of the immune response lymphocytes circulate between the blood and the secondary lymohoid tissues and wait for the next interraction with the antigene in their resting form.

Based on their function and CD markers on their surface T-cells are grupped into these basic T-cell types:

T-helper cells
CD4+, producing many different cytokines. They react to the antigenes presented by the APCs according to the MHC class II and induct the adaptive immune response. Based on the produced cytokines T-helper cells are divided into: T-helper cells are a target for the HIV.
 * T1: promote the cytotoxic and cell immune reaction (macrophages, TC).
 * T2: promote the antibody reaction (B-cells, antibody production).

Cytotoxic T-cells
CD8+, are able do induct apoptosis of the cell, eventually can destroy the cell directly with help of the cytotoxic mechanisms. They react to the MHC class I, control the condition of the cells in the organism (anticancer protection).

Suppressor T-cells
Nonuniform group of the T-cells, during the inflammation most likely develop from the T-helper cells, that's why they're also sometimes called as TH3(r) subset cells. They don't have the specific CD marker, some ot them are CD-4+ and CD-8+, others carry either one of these markers or none of them. Their main task is to moderate and mute the intenzity of the immune reaction. It is implemented with interleukines IL-10 and partially IL-4. Tissue reparation and fibroblast stimulation is accelerated with help of TGF-β (transforming growth factor).

Natural killer T-cells, NKT
The main components of the cytotoxic cell immunity. They're able to attack without previous meeting with the antigene (occures in the newborns). Although they're lymphocytes, they belong to the innate immune system. NKT don't have the CD-3 marker on their surface. Morfologically they're large lymphocytes (12–14 μm).