Mitogens stimulate cell division in B and T cells . While antigens can only activate the B and T cells via specifically binding receptors (real immune response), mitogens react by stimulating these cell types (no specific immune response). Because of this ability, they are called polyclonal activators.
An important group of mitogens are the lectins (sugar-binding proteins), which bind specifically to membrane glycoproteins of various cells, including lymphocytes . Lectins often lead to agglutinations, which leads to cell activation and proliferation . Some lectins specifically activate B cells, others only T cells, and still others activate both cell types.
Well-known lectins are:
- Concanavalin A (ConA) (T cell activation only)
- Phytohemagglutinin (PHA) (T-cell activation only)
- Pokeweed mitogen (PWM = pokeweed ) (B and T cell activation).
Not all mitogens are lectins. The lipopolysaccharides (LPS) from cell walls of Gram-negative bacteria have a mitogenic effect on B cells. So-called superantigens are the most potent T-cell mitogens. They link the major histocompatibility complex (MHC II) of an antigen presenting cell (APC) and the T cell receptor of a helper or cytotoxic T cell by attaching themselves to the outside of the two molecules. The binding is antigen-independent. The T cells are activated and produce excess cytokines .
Well-known superantigens include enterotoxin A or the TSS toxin from Staphylococcus aureus , which can cause the toxic shock syndrome (TSS), which can be fatal under certain circumstances , and staphylococcal enterotoxin B (SEB).
- Janis Kuby: Immunology (Third Edition) . WH Freeman and Company, USA 1997, ISBN 0-7167-2868-0 .