T Helper Cells - Immunology - Part 5/10

#Immunology #Thelpercells #CD4 #Bcells #Lymphocytes #Plasmacells #Immunesystem #Immuneresponse #Tcells #Tcellactivation #Tcelldevelopment Like this video? Sign up now on our website at ​ to access 800 Exclusive videos on Basic Medical Sciences & Clinical Medicine. These are premium videos (NOT FROM YOUTUBE). All these videos come with English subtitles & download options. The T helper cells (Th cells), also known as CD4 cells or CD4-positive cells, are a type of T cell that play an important role in the immune system, particularly in the adaptive immune system. As their name suggests, they “help“ the activity of other immune cells by releasing cytokines, small protein mediators that alter the behavior of target cells that express receptors for those cytokines. These cells help to polarize the immune response into the appropriate kind depending on the nature of the immunological insult (virus vs. extracellular bacterium vs. intracellular bacterium vs. helminth vs. fungus vs. protist). They are generally considered essential in B cell antibody class switching, breaking cross-tolerance in dendritic cells, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages and neutrophils. Mature Th cells express the surface protein CD4 and are referred to as CD4 T cells. Such CD4 T cells are generally treated as having a pre-defined role as helper T cells within the immune system. For example, when an antigen-presenting cell displays a peptide antigen on MHC class II proteins, a CD4 cell will aid those cells through a combination of cell to cell interactions (e.g. CD40 (protein) and CD40L) and through cytokines. B cells, also known as B lymphocytes, are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system. B cells produce antibody molecules; however, these antibodies are not secreted. Rather, they are inserted into the plasma membrane where they serve as a part of B-cell receptors. When a naïve or memory B cell is activated by an antigen, it proliferates and differentiates into an antibody-secreting effector cell, known as a plasmablast or plasma cell. Additionally, B cells present antigens (they are also classified as professional antigen-presenting cells (APCs)) and secrete cytokines. In mammals, B cells mature in the bone marrow, which is at the core of most bones. In birds, B cells mature in the bursa of Fabricius, a lymphoid organ where they were first discovered by Chang and Glick, which is why the ’B’ stands for bursa and not bone marrow as commonly believed. B cells, unlike the other two classes of lymphocytes, T cells and natural killer cells, express B cell receptors (BCRs) on their cell membrane. BCRs allow the B cell to bind to a specific antigen, against which it will initiate an antibody response. The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, distinguishing them from the organism’s own healthy tissue. Many species have two major subsystems of the immune system. The innate immune system provides a preconfigured response to broad groups of situations and stimuli. The adaptive immune system provides a tailored response to each stimulus by learning to recognize molecules it has previously encountered. Both use molecules and cells to perform their functions.