Lecture 4 Introduction To The Immune System

**[Introduction to the Immune system]** What is Immunity? - the molecules, cells, and tissues that mediate immune reactions work together to mediate an immune response - Resistance to pathogens - Reactions to non-infectious disease - Harmless components of environment like aller...

**[Introduction to the Immune system]** What is Immunity? - the molecules, cells, and tissues that mediate immune reactions work together to mediate an immune response - Resistance to pathogens - Reactions to non-infectious disease - Harmless components of environment like allergy - Tumors - Unaltered components of oneself like autoimmunity What are some immune system functions? What are vaccines? Give examples - Trains the immune system to prevent new infections - eradicated smallpox - helps control SARS-CoV-2 infection - Diptheria, measles, mumps, rubella, pertussis, polio, tetanus, Hep b, Influenza type B. What are the two arms of immune responses? - Innate - immediate protection, non-specific - always present in healthy people - blocks entry of microbes - no response enhancements - rapidly eliminates microbes that enter tissues - time course: 0-12hrs post infection - Adaptive - specific to pathogen, acquired - requires proliferation, - differentiation of immune cells (lymphocytes) - adapts to a microbe's presence - time course: 12hrs to 7 days post infection Do these systems work independently or collaboratively? - A combination of innate and adaptive components of the immune system is required to carry out the functions of the immune system. - These components work both independently and collaboratively What is involved in the innate Immune system? - Epithelial barriers with natural antibiotics (skin; cells lining nose, mouth, GI tract) - Complement- system of molecules that can directly destroy microbes - Innate-Like Lymphoid cells (ILCs), including NK cells, as well as innate T cells (gd T, iNKT) directly kill pathogen-infected cells, secrete cytokines in response to 'danger' signals - Dendritic cells and other phagocytes (myeloid cells) engulf (eat!) pathogens, present pieces to lymphocytes What is involved in the adaptive immune system? - Note: vaccine efficiency linked to secreted antibody. - Helper T-lymphocytes are CD4+ T cell and Cytotoxic T-lymphocytes are CD8+ T cell What are the properties of the adaptive immune system? How can our immune system recognize anything and everything? - Receptor Diversity and Clonal Selection Screen Shot 2021-01-12 at 3.49.23 PM.png How is B cell immune memory generated? - T and B cells proliferate and differentiate after recognition of antigen to become effector cells. These differentiated cells are also referred to as memory cells, as they will respond more quickly when re-exposed to antigen a second time. Screen Shot 2021-01-12 at 3.52.07 PM.png What is the antibody structure and function? - Heavy chain determines immunoglobulin isotype  What are the different isotypes? What are the different antibody functions? - Antibody-dependent cell-mediated cytotoxicity (ADCC) -- killing of antibody coated cells by immune cells that bind Fc. - Direct anti-microbial killing -- antibodies bind and kill pathogens. - Opsonization -- coating of pathogens by antibodies and subsequent phagocytosis. - Activation of complement -- antibody coated pathogens can activate complement cascade and be killed by complement proteins. - Virus/toxin neutralization -- binding of antibodies can prevent virus replication or toxin entry into cells. - Immune modulation -- binding of antigen-bound antibodies to B cells through Fc can shut down immune response. Explain the example of generating an immune response of COVID-19 mRNA vaccines What is the difference between active and passive immunity? Give an example - Active immunity is an adaptive response to an immunological stimulus, e.g. microbial infection or vaccine long-lasting (months-years) - Passive immunity is the transfer of active immunity in the form of antibodies or cells from one person to another, e.g. transfer of maternal antibodies to fetus, or administration of pre-formed antibodies short lasting (\~days-months) - Example: Define the following - Antigen -- a substance that is bound by antibodies (or B or T cell receptors) - Epitope -- the specific portion of an antigen to which an antibody bind - Immunogen -- an antigen that can induce an immune response - Adjuvant -- substance that enhances immune responses to antigens - Hapten -- a small molecule that elicits an immune response if coupled to a larger molecule What is the process of maturation and tissue distribution of lymphocytes? Where are the lymphocytes? - 50 Intestine, 10 Liver, 30 Lungs, 10 Blood, 20 Skin, 190 lymph nodes, 70 spleen, 50 bone marrow What happens to thymic output with age? - It decreases with age