T cell

T cells (also known as Thymocytes cells) or T lymphocytes are a type of lymphocyte (in turn, a type of white blood cell) that play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T-cell receptor (TCR) on the cell surface. They are called T cells because they mature in the thymus (although some also mature in the tonsils). The several subsets of T cells each have a distinct function. The majority of human T cells rearrange their alpha/beta T cell receptors and are termed alpha beta T cells and are part of adaptive immune system. Specialized gamma delta T cells, which comprise a minority of T cells in the human body (more frequent in ruminants), have invariant TCR (with limited diversity), can effectively present antigens to other T cells and are considered to be part of the innate immune system.

Types

Helper

T helper cells (T_H cells) assist other white blood cells in immunologic processes, including maturation of B cells into plasma cells and memory B cells, and activation of cytotoxic T cells and macrophages. These cells are also known as CD4⁺ T cells because they express the CD4 glycoprotein on their surfaces. Helper T cells become activated when they are presented with peptide antigens by MHC class II molecules, which are expressed on the surface of antigen-presenting cells (APCs). Once activated, they divide rapidly and secrete small proteins called cytokines that regulate or assist in the active immune response. These cells can differentiate into one of several subtypes, including T_H1, T_H2, T_H3, T_H17, Th9, or T_FH, which secrete different cytokines to facilitate different types of immune responses. Signalling from the APC directs T cells into particular subtypes.

3T3 cells

3T3 cells come from a cell line established in 1962 by two scientists then at the Department of Pathology in the New York University School of Medicine, George Todaro and Howard Green. The 3T3 cell line has become the standard fibroblast cell line. Todaro and Green originally obtained their 3T3 cells from Swiss albino mouse embryo tissue.

Nomenclature

The '3T3' designation refers to the abbreviation of "3-day transfer, inoculum 3 x 10⁵ cells." This cell line was originally established from the primary mouse embryonic fibroblast cells that were cultured by the designated protocol, so-called '3T3 protocol'. The primary mouse embryonic fibroblast cells were transferred (the "T") every 3 days (the first "3"), and inoculated at the rigid density of 3 x 10⁵ cells per 20-cm² dish (the second "3") continuously. The spontaneously immortalized cells with stable growth rate were established after 20-30 generations in culture, and then named '3T3' cells. Specifically, "3T3-L1" is one of the current lines.

Cytotoxic T cell

A cytotoxic T cell (also known as T_C, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8+ T-cells or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected (particularly with viruses), or cells that are damaged in other ways.

Most cytotoxic T cells express T-cell receptors (TCRs) that can recognize a specific antigen. An antigen is a molecule capable of stimulating an immune response, and is often produced by cancer cells or viruses. Antigens inside a cell are bound to class I MHC molecules, and brought to the surface of the cell by the class I MHC molecule, where they can be recognized by the T cell. If the TCR is specific for that antigen, it binds to the complex of the class I MHC molecule and the antigen, and the T cell destroys the cell.

In order for the TCR to bind to the class I MHC molecule, the former must be accompanied by a glycoprotein called CD8, which binds to the constant portion of the class I MHC molecule. Therefore, these T cells are called CD8+ T cells.