Lymphocytes are a type of white blood cell in the vertebrate immune system. Under the microscope, lymphocytes can be divided into large granular lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells, NK cells. Small lymphocytes consist of T cells and B cells.
NK cells are a part of innate 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 histo-compatibility complex, class I. NK cells are activated in response to a family of cytokines called interferon's. Activated NK cells release cytotoxic, cell-killing, granules which then destroy the altered cells. They were named "natural killer cells" because of the initial notion that they do not require prior activation in order to kill cells which are missing MHC class I.
T cells and B cells are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humeral immunity, relating to antibodies. The function of T cells and B cells is to recognize specific non-self antigens, during a process known as antigen presentation. Once they have identified an invader, the cells generate specific responses that are tailored to fully eliminate specific pathogens or pathogen infected cells. B cells respond to pathogens by producing large quantities of antibodies which then neutralize foreign objects like bacteria and viruses. In response to pathogens some T cells, called T helper cells, produce cytokines that direct the immune response while other T cells, called cytotoxic T cells, produce toxic granules that contain powerful enzymes which induce the death of pathogen infected cells.
A low normal to low absolute lymphocyte concentration is associated with increased rates of infection after surgery or trauma.
One basis for low T cell lymphocytes occurs when the human immunodeficiency virus, HIV, infects and destroys T cells, specifically the CD4+ subgroup of T lymphocytes. Without the key defense that these T cells provide, the body becomes susceptible to opportunistic infections that otherwise would not affect healthy people. The extent of HIV progression is typically determined by measuring the percentage of CD4+ T cells in the patient's blood. The effects of other viruses or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in the blood.
NK cells are a part of innate 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 histo-compatibility complex, class I. NK cells are activated in response to a family of cytokines called interferon's. Activated NK cells release cytotoxic, cell-killing, granules which then destroy the altered cells. They were named "natural killer cells" because of the initial notion that they do not require prior activation in order to kill cells which are missing MHC class I.
T cells and B cells are the major cellular components of the adaptive immune response. T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humeral immunity, relating to antibodies. The function of T cells and B cells is to recognize specific non-self antigens, during a process known as antigen presentation. Once they have identified an invader, the cells generate specific responses that are tailored to fully eliminate specific pathogens or pathogen infected cells. B cells respond to pathogens by producing large quantities of antibodies which then neutralize foreign objects like bacteria and viruses. In response to pathogens some T cells, called T helper cells, produce cytokines that direct the immune response while other T cells, called cytotoxic T cells, produce toxic granules that contain powerful enzymes which induce the death of pathogen infected cells.
A low normal to low absolute lymphocyte concentration is associated with increased rates of infection after surgery or trauma.
One basis for low T cell lymphocytes occurs when the human immunodeficiency virus, HIV, infects and destroys T cells, specifically the CD4+ subgroup of T lymphocytes. Without the key defense that these T cells provide, the body becomes susceptible to opportunistic infections that otherwise would not affect healthy people. The extent of HIV progression is typically determined by measuring the percentage of CD4+ T cells in the patient's blood. The effects of other viruses or lymphocyte disorders can also often be estimated by counting the numbers of lymphocytes present in the blood.
