Lymphocytes of these types directly destroy appropriate target cells, or help generate cells that do.
T4 Helper Cells
T-lymphocytes with the T4 protein on their surface which recognizes the antigenic peptide while the CD4 molecule recognizes the major histocompatibility complex (MHC-II) molecule. These "helper T-lymphocytes" cause the production of more cells for cell-mediated immunity, but they first must be activated by cytokines, such as interleukin-1 (Il-I).
As well as being invoked by cytokines, they generate cytokines:
- Interleukin-2 (Il2)
- Tumor necrosis factor-alpha (TNFa)
- B-cell growth factor (BCGF)
- B-cell differentiation factor (BCDF)
T8 Killer cells
CD8-protein containing lymphocytes, also called T8-lymphocytes, are a subset of circulating "killer cells". All CD8-cells are killers, but other killer cells may be monocytes, macrophages (derived from monocytes) or polynuclear neutrophils. The key is that a killer cell attacks material labeled with the B-lymphocyte generated antibody.
These cytotoxic lymphocytes may be generated in vitro in mixed lymphocyte cultures (MLC), in vivo during a graft-versus-host (GVH) reaction, or after immunization with an transplantation#allograft, tumor cell or virally transformed or chemically modified target cell. The manner in which these cells destroy targets is sometimes called cell-mediated lympholysis (CML).
- Anonymous (2015), Lymphocyte (English). Medical Subject Headings. U.S. National Library of Medicine.
- Anonymous (2015), Lymphocyte count (English). Medical Subject Headings. U.S. National Library of Medicine.
- Kaiser, Gary E., T4 -Lymphocytes (T4-Cells; T4-Helper Cells; CD4+ Cells), "The adaptive immune system: I. Introduction, B. Major cells and key cell-surface molecules involved in adaptive immune responses", Doc Kaiser's Microbiology Home Page