Lymphocytes are a type of white blood cells that provide immunity and help protect the body against pathogens. They can be found in the blood and in lymph tissue. There are three major types of lymphocyte – T cells, B cells and natural killer (NK) cells.
B lymphocytes are primarily responsible for immunity relating to antibodies (humoral immunity). During an immune reaction B cells produce plasma cells and memory cells. Plasma cells are specialized in producing antibody, and B memory cells ‘remember’ specific pathogens and start a strong and rapid response to them during subsequent infections. Memory cells give our body immunity against the invader. T lymphocytes, also called T cell and thymocyte, help control immune responses and help kill tumour cells. The killer T cells are specialized in attacking viruses and sometimes also bacteria. They may also help fight cancer. Helper T cells are the main regulators of the immune response. They activate killer T cells and B lymphocytes. NK cells provide faster immune reaction. They recognise and attack viral-infected cells even in the absence of antibodies and MHC (major histocompatibility complex) present on the infected cell surfaces. They also respond to tumour formation.
Malnutrition and some immunodeficiency diseases are generally associated with low lymphocyte count whereas some devastating conditions, like cancers (multiple myeloma, lymphocytic leukaemia) and autoimmune disorders leads to the activation of high amount of lymphocytes in the blood.