KAUR NAVNEET SCHNEIDER STARLA The Immune System

Overview: Reconnaissance, Recognition, and Response Immune system: a system that enables animals to avoid/limit infections and ailments; defense system made up of proteins, immune cells, etc. Pathogens: unwanted substances that cause disease via infection Two types of immunity:  Innate Immunity  Acquired Immunity

43.1: In innate immunity, recognition and response rely on shared traits of pathogens Innate immune responses included barrier defenses as well as defenses to combat pathogens that enter the body 1. Barrier defenses  Skin and the mucous membranes (anything on the surface, any lining of the openings)  Gives an animal a physical barrier, and secretions also help protect against infection (results in skin pH of 3-5) 2. Cellular innate defenses  Fight pathogens that make it past the barrier (cuts, gashes, burns)  Includes white blood cells and antimicrobial proteins

There are problems with just relying on the barrier system!

43.1 Continued: Innate Immunity in Invertebrates Innate defenses include  Exoskeletons  Chitin-based barriers in insect intestines  Lysozymes: enzymes that digest the cell walls of microbes  Low pH in organs  Hemocytes: immune cells in the hemolymph (insect blood); capable of phagocytosis  Secretion of antimicrobial peptides that disrupt pathogen membranes

43.1 Continued: Phagocytic White Blood Cells Neutrophils are white blood cells that ingest and destroy microbes in a process called phagocytosis Monocytes are another type of phagocytic leukocyte. They migrate into tissues and develop into macrophages, which are giant phagocytic cells Eosinophils are leukocytes that defend against parasitic invaders (worms, jungle worms) by positioning themselves near the parasite’s wall and discharging hydrolytic enzymes

43.1: Antimicrobial Proteins Interferon proteins are the proteins that help the innate defense system to fight the viral infections.  They cause cells adjacent to infected cells to produce substances to inhibit viral replication. complement system consists of 30 proteins; one of the functions include the lyse invading cells

43.1 Continued A local inflammatory response is triggered by damage to tissue from a physical injury or the entry of pathogens (cuts, burns)  It leads to release of numerous chemical signals  Histamines are releases by basophils and mast cells (these are 2 types of leukocytes) in response to an injury.  Histamines trigger the dilation and permeability of nearby capillaries. This aids in delivering clotting agents and phagocytic cells to an injured area.  Systematic inflammatory responses include fever and septic shock Natural killer (NK) cells help recognize and remove diseased cells

Histamines!

43.2: In acquired immunity, lymphocyte receptors provide pathogen-specific recognition Vertebrates have 2 types of lymphocytes: B cells & T cells  B lymphocytes (B cells) are responsible of producing antibodies that fight infections  Most common in the blood and proliferates in the bone marrow  T lymphocytes (T cells) responsible in killing the foreign substances that enter the body All blood cells come from stem cells in the bone marrow Antigens are foreign molecules that elicit a response by lymphocytes. B and T cells recognize them by specific receptors imbedded in their plasma membranes. Antibodies are soluble proteins secreted by B cells during an immune response.

B and T Lymphocytes

43.2 Continued B- or T-cell activation occurs when an antigen binds to a B or T cell. B-cell activation is enhanced by cytokines.  In clonal selection, a lymphocyte creates two clone cells. The result of clonal selection is a mass of cells specifically designed to target that antigen. There are two types:  Effector cells: responsible for fighting the antigen  Memory cells: these cells stay in the body, inactive long after the antigen is gone, with receptors that will recognize the antigen if it enters the body again; aids a body in generating a quick response to infections

A memory cell doing it’s job…

MHCs Antigen-presenting cells: Upon recognizing a pathogen (ingesting it, internalizing some pathogen byproducts), MHCs bind to them so T cells can recognize them; usually B cells Major histocompatability complex molecules (MHCs): Molecules generated by genes (unique to every individual), help display antigens and trigger T-cell response; grafting foreign MHCs can aid in generating new immune responses; can lead to rejected transplants  Class I: Found in all cells minus red blood cells  Class II: Found in macrophages, B cells, dendritic cells (more common)

Why do we have so many different types of B cells and T cells? Gene shuffling and genetic recombination! We have more than 1 million different types of B cells! And, we have more than 10 million different types of T cells!

Immune Responses: A single B or T cell only responds to ONE antigen! Primary immune response: Upon first exposure to an antigen; lymphocyte activated Secondary immune response: When the same antigen appears in the body later; this response is greater in response time and magnitude

43.3: Acquired immunity defends against infection of body cells and fluids Two branches:  Humoral immune response: antibodies are produced to go around the body; activation and clonal selection of effector B cells happens in this response  Cell-mediated immune response: the body searches for and destroys antigens; activation and clonal selection of cytotoxic T cells happens in this response Helper T cells: Help both responses work; they secrete cytokines after interacting with class II MHC molecules; bound by a CD4 protein Cytokines: activate B cells and cytotoxic T cells Cytotoxic T cells: bind to class I MHCs; destroys infected cells (either pathogen infection or cancer); bound by CD8 proteins

43.3 Cont’d Activated B cells produce memory cells and plasma cells Plasma cells: involved in secreting mass amounts of antibodies, which go throughout the body destroying antigens Antibodies work by:  Neutralization: They bind to the pathogen by the pathogen’s proteins, this stops the pathogen from entering and damaging cells  Opsonization: stimulates greater phagocytosis, eating the antigens faster  Lysis: activates the complement system (a group of proteins that fight infection)

Different Types of Immunity; Important things to remember Active Immunity: Develops naturally or artificially (via vaccination) in response to an infection Passive Immunity: antibodies are passed into the individual (like infants receiving it via milk) Some antigens exist on red blood cells (which helps determine type), so blood transfusions can be rejected if the host body has non-self blood antibodies to attack these foreign blood cells based on their antigens  So, in order to make sure transplants go OK, doctors should match the MHC molecules with the donor, because MHC molecules are primarily responsible for rejecting transplants

43.4 Disruptions in immune system function can elicit or exacerbate disease How do localized allergies work?  When an allergen first enters the body, IgE antibodies are created. When the allergen leaves, these antibodies produce molecules that bind to receptors on mast cells, so the next time an allergen enters the body, it triggers these IgE molecules, producing an allergic reaction! (Histamine production, swelling, vascular changes, etc.) What are autoimmune diseases?  The body turns against itself, producing antibodies to target molecules in the body.  Lupus, rheumatoid arthritis, multiple sclerosis, HIV/AIDS (attacks helper T cells)

HIV attacking a helper T cell