Limfòcits

Limfòcits are a type of white blood cell that play a central role in the adaptive immune system. They comprise the main lymphocyte subtypes: B limfòcits (B cells), T limfòcits (T cells), and natural killer (NK) cells. B cells produce antibodies; T cells mediate cellular immunity through helper, cytotoxic, and regulatory roles; NK cells provide rapid responses against infected or transformed cells.

B limfòcits mature in the bone marrow, while T limfòcits mature in the thymus. Upon encountering antigens, B cells differentiate into plasma cells that secrete antibodies and into memory B cells. T cells are activated by antigen presentation and differentiate into various effector subsets: helper T cells coordinate responses, cytotoxic T cells destroy infected or abnormal cells, and regulatory T cells dampen immune activity.

Limfòcits circulate in the blood and lymph and populate lymphoid organs such as lymph nodes, the spleen, and mucosa-associated lymphoid tissue. They recognize antigens through surface receptors: B cells express B cell receptors (surface immunoglobulins); T cells express T cell receptors. Memory lymphocytes persist after infection or vaccination, enabling faster responses to subsequent encounters.

Deficiencies or malignancies involving limfòcits can affect immune function or cause disease, such as immunodeficiencies that reduce antibody production or lymphoproliferative disorders like lymphomas. Vaccination and infections trigger limfòcits to learn to recognize diverse pathogens, forming the basis of adaptive immunity.