so in today's video we're going to be talking about B cells and T cells so they're both white blood cells and they have a role in immune function so that means that they have a protective role in fighting infections so there are different types of B cells and T cells but they all originate from the same cell and this cell is known as the hematopoietic stem cell which originates in the bone marrow so through differentiation processes this hematopoietic stem cell eventually forms B cells and T cells let's talk about B cells first the main function of B cells is the recognition of antigens after being made in the bone marrow they travel via the bloodstream to organs like the spleen or they're located in lymph nodes and this is usually where they're concentrated in the body on the surface of B cells there are these receptors which are called B cell receptors and these have a function of binding onto antigens if you don't know what an antigen is imagine it's like a small chemical or molecule which is on the surface of harmful bacteria or pathogens or it doesn't have to be on the surface of a pathogen but the body recognizes it as a foreign substance once an antigen is bound onto the B cell receptors the antigen is engulfed into the B cell in a process called receptor mediated endocytosis the B cell then breaks down the antigen and the breakdown products are then placed on the surface of the B cell in a special type of molecule called a major histocompatibility complex and in B cells is the second class of major histocompatibility complex which is present the reason that this occurs is it allows helper T cells which are also known as cd4 lymphocytes to recognize and bind onto the major histocompatibility complex class 2 and once it's bound it releases lymphokines lymphokines are important because it causes this B cell with these specific b-cell receptors to clone itself via the process of mitosis so that we have more of these B cells with the same receptors and it causes the B cells to differentiate into plasma cells and the main function of my cells are to release antibodies these antibodies that are produced by the plasma cells are specific to the antigen that was initially bound onto the B cell in the first place now let's talk about t-cells we just mentioned one type of t cell called the helper T cell also known as cd4 T cells and just to recap it binds on to the second class of major histocompatibility complex which is a molecule located on the surface of B cells and this binding causes the release of lymphokines what the types of T cells include the cytotoxic T cell also known as cd8 t-cells in the case of cytotoxic T cells or cd8 imagine you have a cell infected by a virus the cell is now infected and it contains viral DNA and viral mRNA because of this the virus is now making viral proteins and peptides since all cells with a nucleus have major histocompatibility complex class 1 on their membrane these viral proteins that the infected cell is making is presented by the class 1 major histocompatibility complex molecule on the surface of the infected cell so even though that sounds very confusing imagine the infected cell is kind of giving a warning signal by showing the infected proteins on its membrane the cytotoxic cd8 cells have T cell receptors on their surface that recognize the peptide on the surface of the infected cell is not normal so it binds onto it and when it binds the T cell either secretes cytotoxins like perforin or granulysin which initiates programmed cell death in a process called apoptosis or once the binding occurs the T cell expresses a protein called fast ligand or FAS ligand which binds onto the FAS molecule present on the infected cell and this forms the death inducing signaling complex and eventually we have apoptosis of the cell we also have memory T cells and there are different types but the main thing that you need to know is that they are able to replicate very fast and initiate their response very rapidly if they've mounted the antigen before the final point that we're gonna make is that both B and T cells are part of the body's natural adaptive immunity which means they're are part of a specialized network of cells that specifically respond to pathogens and specifically fight off infections