Lymphocytes

Abstract

Lymphocytes are white blood cells that are derived from a common lymphoid progenitor in the bone marrow. They function as specific mediators involved in inducible immune responses against infectious agents. The classically defined adaptive B and T lymphocytes use defined surface molecules, antigen receptors, to detect antigens. The activation of lymphocytes requires multiple signals, including binding of the antigen‐specific receptor to the antigen, costimulation and/or exposure to environmental molecules. Activation results in an expansion of clonally reactive cells, which become effector cells (plasma cells and activated T cells) that function to eliminate pathogens, or which become memory cells to facilitate later secondary responses. A secondary group of lymphocytes, the innate lymphocytes (natural killer (NK) cells, γδ T cells, invariant NK T cells and B‐1 cells) also play a role in immune function. Specifically, they represent a pool of cells that respond quickly to a limited repertoire of antigens at sites of infection. Key Concepts: Cells of the lymphoid lineage are derived from the common lymphoid progenitors that differentiate from multipotent haematopoietic stem cells in the bone marrow. The role of lymphocytes is to facilitate recognition of foreign antigens (immune stimulators) and to mount responses for their neutralization and/or elimination. The developmental stages of B and T cells correspond to gene rearrangement events, leading to the different specificity of B cell and T cell receptors. B cells mature in the bone marrow, whereas T cells undergo education and maturation in the thymus. B lymphocytes utilise an immunoglobulin receptor to recognise conformational antigens. Upon activation, they mature into plasma cells to secrete specific antibodies with directed target specificity. T lymphocytes recognised processed antigen presented via major histocompatibility molecules. Multiple phenotypic subsets exist, allowing for differential regulation of cellular immune function. T‐helper cells express CD4 molecules, and assist in both cellular and humoral functions. Specific helper activity is directed via secretion of pleiotropic cytokines. Cytotoxic T cells express CD8 molecules, and target viral infected or tumour targets for destruction. All T lymphocytes bear the CD3 molecule to assist in signalling once antigen is encountered. The primary response of lymphocytes leads to the generation of ‘daughter clones’, which become effectors, a small fraction of which become memory cells. This generates a persistent population that can rapidly expand and respond with higher magnitude upon secondary encounter with an antigen. The innate lymphocytes (natural killer cells, γδ T cells, invariant natural killer T cells and B‐1 cells) represent a special reservoir of cells that are able to respond quickly to a limited subset of antigens at sites of infection.

Delayed-Type Hypersensitivity to Metals of Environmental Burden in Patients with Takotsubo Syndrome – Is There a Clinical Relevance?

“…Chronic hypersensitivity reactions are accompanied by inflammatory reactions with the production of many cytokines and an increased oxidative stress [32]. A decreased performance or even the “exhaustion” of the methionine-homocysteine cycle, for example as a consequence of chronic inflammatory reaction and increased oxidative stress, as indicated above, can lead to a decreased degradation of catecholamines, among others, and therefore to an elevation of their plasma levels and an increase in their toxicity.…”

Current Progress in Non-viral RNAi-Based Delivery Strategies to Lymphocytes

“…They recirculate between the blood and lymphatic systems to invade and target damaged tissues and tumor cells upon appropriate signals. 1 Lymphocytes can be divided into innate and adaptive immune cells, which differ in both specificity and function. While adaptive lymphocytes can respond to a significantly higher number of antigens in comparison to innate lymphocytes, the response is slower due to its multi-step nature.…”

“…The latter eliminates path-ogens and facilitates secondary immune responses upon becoming memory cells. 1 Lymphocytes are associated with the pathogenesis of autoimmune diseases, allergies, graft versus host disease, inflammation, lymphotropic viral infection (e.g., HIV), and cancer. 2,3 For example, the entry of HIV is mediated by a specific subset of T lymphocytes.…”