Question

Topic 3. Tell the "T cell story". In particular, where are they born? Where do they receive their education? What are the two criteria for "graduation"? When do they stop being naïve mature T cells? What two things must happen for a T cell to become "activated"? Which type of activated cell participates in humoral immunity? What does the other type of activated T cell participate in?

Answer 1

T cells are formed in the bone marrow, T Progenitor cell migrate to the thymus to mature and become T cells. In the thymus T cells multiply and diffrentiate to form, helper T cell, regulatory T cell or cytotoxic T cell or to become memory cells. Than they are sent to peripheral tissues or circulate in the blood or lymphatic system and than they are stimulated by appropriate antigen.

Immature T cells do not express theire antigen, they are known as double negative cells (CD 8 + CD4+), through the process of development they become double positive cells than they mature into single positive (CD8+ CD4-, or CD8- CD4+) thymocytes and they are released to peripheral tissues, most thymocytes die through the process development, the remaining 2% go on to become mature T cells.

Unlike antibodies whch can bind to antigen directly, T cells can only recognize antigens that are bound to a receptor molecule called Major histocompatblity complex, Class 1 (MHC1) and Class 2 (MHC2) these MHC molecules are called Antigen presenting cells. In addition to this they require number of secondary signal to be activated. So T cells are activated when T cell receptor is combined with co-stimulatory molecule such as CD 28 by MHC2 peptide and co-stimulatory molecule of antigen presenting cell, Co-stimulation is necessary for T cell activation.

Helper T cells participates in humoral immunity, in which assistance from helper T cells, B cells are activated