[Music] the immune system is responsible for fighting infection and disease it is comprised of many specialized cell types all which work together to keep your body healthy in this short video you will be introduced to the major cellular players of the immune system let's start by introducing the two major arms of the immune system innate and adaptive immunity innate immunity serves as the first line of defense and is a more general immune response you might recognize some of the classic symptoms of an a immunity such as fever and inflammation adaptive immunity allows for very specific
detection and elimination of pathogens however it takes a longer time to ramp up than innate immunity importantly the adaptive immune system provides immunological memory the ability of our immune cells to remember previous infections and clear them more quickly in the future [Music] all immune cells develop from a single pluripotent cell in the bone marrow the hamada products stem cell hamada products stem cells give rise to lymphoid and myeloid progenitors each of which differentiate into a range of immune cell types we refer to the cells on the top as a lymphoid lineage whereas the cells in
the bottom are classified as the myeloid lineage the myeloid progenitors also give rise to red blood cells and platelets although we won't focus on those here let's now look closely at the lymphoid lineage the lymphoid progenitor differentiates into three cell classes we'll start by introducing b-cells upon activation mature B cells differentiate into memory cells or plasma cells plasma cells are the immune cells that are responsible for secreting antibodies an important component of adaptive immunity natural killer cells are cytotoxic cells of the innate immune system they detect virus infected cells and kill them t-cells arise from
a common progenitor there are many types of mature t-cells but the best known ones those which we'll cover here include memory T cells cytotoxic T cells and helper T cells like memory b-cells a fraction of maturity cells remain in the body as memory t-cells to help the body mount a faster immune response in future infections cytotoxic T cells recognize antigen or small pathogen derived particles on infected cells and kill them in a pathogen specific manner lastly upon activation by specialized cells in the body helper T cells secrete cytokines that boost the adaptive immune response for
example helper T cells play an important role in visa activation now let's take a look at the myeloid lineage the myeloid lineage produces most cells of the innate immune system as well as important antigen presenting cells that prime the adaptive immune response the myeloid progenitor gives rise to neutrophils which are innate immune cells that specialized in the capture and killing of microorganisms throughout the body eosinophils which are a type of granulocyte that releases cytokines to defend against parasites and monocytes which further differentiate into dendritic cells and macrophages dendritic cells are specialized to type a phagocytic
cell that bridges innate and adaptive immunity macrophages are tissue resident phagocytic cells they patrol the body and assist in cleaning of infection and activating other immune cells other cells that arise from the myeloid progenitor include masked cells another type of granulocyte that are implicated in an allergy as well as basophils which are a less well understood cell type that is involved in the immune response to parasites so how our immune cells activated here we'll briefly cover the molecular paradigms for innate and adaptive immune activation cells of the innate immune system Express molecules known as pattern
recognition receptors at their surface these receptors bind pathogens are parts of pathogens which induce intracellular signals that activate an innate immune response the particles recognized by these receptors are common amongst pathogens to activate adaptive immunity cells present antigen small peptide fragments of pathogens to t-cells to inform a specific immune response antigen is presented by two types of surface molecules MHC class 1 and MHC class 2 MHC class 1 molecules are expressed by all cells in the body and are used in defense against intracellular pathogens such as viruses they do this by presenting endogenous or intracellular
antigens to cytotoxic T cells MHC class 2 molecules present exogenously gen which is antigen found on pathogens outside of cells and activate helper T cells MHC class 2 molecules are expressed by what are known as professional antigen presenting cells which include dendritic cells macrophages and b-cells there are safeguards in place to ensure that the immune system is inactivated against self antigens the mammalian immune system is comprised of a complex set of cells that contribute to innate and adaptive immunity the foundational understanding you've gained from this video serves as a starting point for a deeper look
at this topic [Music] you
