Lymphocytes
T-lymphocyte, B-lymphocyte (also known as T cell and B cell) and natural killer (NK cells).
A lymphocyte is a type of white blood cell in the vertebrate immune system. Lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells (NK cells). Small lymphocytes consist of T cells and B cells.
The function of T cells and B cells is to recognize “non-self” specific molecules or particles (called Antigens). Once they have identified an invader, the cells generate specific responses (immune response) to eliminate specific pathogens or pathogen-infected cells. B cells respond to pathogens by producing large antibodies that then neutralize foreign objects like bacteria and viruses. In response to pathogens some T cells produce toxic granules that contain powerful enzymes (proteins), which induce the death of pathogen-infected cells.
NK cells are also a part of the immune system and play a major role in defending the host from both tumors and virally infected cells. NK cells distinguish infected cells and tumors from normal and uninfected cells by recognizing changes of a surface molecule called MHC (major histocompatibility complex) class I. Activated NK cells release cytotoxic (cell-killing) granules which then destroy the altered cells if they are missing the MHC class 1.
NK cells (natural killer)
Target: infected cells
Role: to kill cells that appear to be abnormal
B cells
Target: microorganisms and infected cells
Role: to secrete antibodies that attach to microorganisms or cells thereby helping to destroy them
Cytotoxic T lymphocytes
Also called: CD8+ T cells
Target: infected cell
Role: to kill infected cells
T helper type 2 lymphocytes (Th2)
Character: Captain of the B lymphocytes (bearing a small crest of Robin Hood on their sweaters)
Th2 cells, which produce IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13, evoke strong antibody responses (including those of the IgE class) and eosinophil accumulation.
Th2-dominated responses play a pathogenic role in both progressive systemic sclerosis and cryptogenic fibrosing alveolitis, and favor a more rapid evolution of HIV infection towards the full-blown disease
T helper type 1 lymphocytes (TH1)
Character: Captain of the cytotoxic T lymphocytes (bearing a small crest of a marksman on their sweaters)
Produce interferon (IFN)-gamma, interleukin (IL)-2 and tumor necrosis factor (TNF)-beta.
Th1-dominated responses are involved in the pathogenesis of organ-specific autoimmune disorders.
T cells: three different types
