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Cells: Bite-sized Immunology

CD8+ T Cells

CD8+ (cytotoxic) T cells, like CD4+ Helper T cells, are generated in the thymus and express the T-cell receptor. However, rather than the CD4 molecule, cytotoxic T cells express a dimeric co-receptor, CD8, usually composed of one CD8α and one CD8β chain. CD8+ T cells recognise peptides presented by MHC Class I molecules, found on all nucleated cells. The CD8 heterodimer binds to a conserved portion (the α3 region) of MHC Class I during T cell/antigen presenting cell interactions (see Figure 1).

CD4+ T Cells

CD4+T cells recognise peptides presented on MHC class II molecules, which are found on antigen presenting cells (APCs). As a whole, they play a major role in instigating and shaping adaptive immune responses.

B Cells

Early B cell development and commitment to the B cell lineage occurs in the foetal liver prenatally, before continuing in the bone marrow throughout life. B cells are at the centre of the adaptive humoral immune system and are responsible for mediating the production of antigen-specific immunoglobulin (Ig) directed against invasive pathogens (typically known as antibodies).


Basophils are a type of bone marrow-derived circulating leukocyte. They are highly granular mononuclear cells. Basophil differentiation from myeloid progenitors is driven by IL-3 and their expression of IL-3R αchain (also known as CDw123) enables them to be distinguished from mast cells.