Lack the pathogen-specific immune responses seen in mammals

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Howard Park
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1 Plants, Invertebrates, and Vertebrates have multiple nonspecific immune response mechanisms, but. Lack the pathogen-specific immune responses seen in mammals In Innate (non specific) immunity, recognition and response rely on shared pathogen traits -Innate immune responses include barrier defenses as well as defenses to combat any pathogens that enter the body Barrier Defenses -Include skin and the mucous membranes that cover the surface and line the openings of the animal body -These provide a physical barrier to pathogens, produce secretions that result in a skin ph from 2 to 5, and produce the antimicrobial protein lysozyme found in saliva, mucous secretions, and tears (breaks down the cell walls of bacteria) Cellular Innate Defenses -Combat pathogens that get through the barrier defenses- for example, in a cut. They include phagocytic white blood cells (leukocytes) and antimicrobial proteins.

2 A Local Inflammatory Response Natural Killer Cells -A local inflammatory response is triggered by damage to tissue by physical injury or the entry of pathogens -It leads to the release of numerous protein chemical signals -For example, histamines are released in response to injury -Histamines trigger the dilation and permeability of nearby capillaries. This aids in delivering clotting agents and phagocytic cells to the injured area -Natural killer (NK) cells are WBCs that help recognize and remove pathogen infected cells with damaged cell receptors by binding to them and releasing toxins into them. Cellular Innate (non specific) Responses: Phagocytic White Blood Cells Cellular Innate (non specific) Responses: Antimicrobial Proteins -Neutrophils are smaller white blood cells that ingest and destroy microbes in a process called phagocytosis. -Monocytes are another type of phagocytic leukocyte found in the blood. When they migrate into tissues, they develop into macrophages, which are giant phagocytic cells that can attack larger pathogens and tumor cells. -Eosinophils are leukocytes that defend against parasitic invaders such as worms, by positioning themselves near the parasite s wall and discharging hydrolytic enzymes. -Interferon proteins provide innate defense against cells invaded by viruses. These are secreted by infected cells and stimulate neighboring cells to produce proteins that help them defend against the viruses. -The complement system is a group of about twenty proteins that complement defense reactions. These proteins help attract phagocytes to foreign cells and help destroy foreign cells by promoting cell lysis.

3 Acquired (specific) Immunity: Vertebrates have two types of Lymphocytes -Vertebrates have two types of lymphocytes: B lymphocytes (B cells), which proliferate and mature in the bone marrow, and T lymphocytes (T cells), which are made in the bone marrow but mature in the thymus -They circulate through the blood and lymph, and both recognize particular (specific) microbes Antigens -Are foreign molecules that elicit a response by lymphocytes -B and T cells recognize them by specific receptors imbedded in their plasma membrane Antibodies -Are soluble proteins secreted by B cells during an immune response that bind to antigens B- or T- cell activation occurs when an antigen binds to a B or T cell -B-cell activation is enhanced by proteins called cytokines. The B-cells then form two types of cells called plasma and memory cells. -This results in a thousands of B cells with antibodies, all specific to this antigen -Plasma cells are B cells that produce their specific antibodies which then circulate through the body, binding to antigens -Memory cells, are B cells which are long-lived, bear receptors for the same antigen and circulate in the body to quickly mount an immune response in later infections

4 B- Or T- cell Continued -B-cell receptors, or antibodies, bind to antigens on the surface of an invading pathogen, inactivating them. Inactivation is followed by macrophage phagocytosis. -T-cell receptors then bind antigens that are displayed by antigen-presenting cells (like macrophages) on their surface. (Like B cells, the plasma membranes of T cells have antigen receptors. However, these receptors are not antibodies, but recognition sites for molecules displayed by nonself cells.) Specificity of B and T cells -The specificity of B and T cells is a result of the recombination of several gene segments in their DNA that control the shape of their receptor sites and results in more than 1 million different B cells and 10 million different T cells. -Each B or T cell responds to only one specific type of antigen Two Branches of Acquired (specific) Immunity -Humoral immune response involves the activation of memory and plasma B cells, which produce antibodies that circulate in the blood and bind to antigens -Cell-mediated immune response involves the activation of cytotoxic T cells, which identify and destroy infected cells Defending Against Infection -Helper T cells aid both responses. When activated by binding to an anitgen presenting cell they secrete cytokines called interleukins that simulate and activate both B cells and cytotoxic T cells

5 Organize Your Thoughts On Immunity Names -B cells make antibodies, which provide humoral immunity. This helps fight pathogens that are circulating in the blood -Cytotoxic T cells destroy body cells that are infected by a pathogen or cancer cells. -Helper T cells activate both B and T cells Destroying the Antigen -Recall that activated B cells produce memory cells as well as plasma cells. The plasma cells fight the initial pathogens and secrete antibodies in huge numbers during the primary immune response -These antibodies will circulate in the blood, and bind the antigen if encountered again later during the secondary immune response Destroying the Antigen: Primary and Secondary -A primary immune response occurs when the body is first exposed to an antigen and a B or T lymphocyte is activated -A secondary immune response occurs when the same antigen is encountered at a later time. It is faster and of greater magnitude Immunity -Active immunity develops naturally in response to an infection; it also develops artificially by immunization (vaccination). In immunization, a nonpathogenic form of a microbe of part of a microbe elicits an immune response resulting in immunological memory for that microbe. -Passive immunity occurs when an individual receives antibodies, such as those passed to the fetus across the placenta and to infants via milk.

6 HIV and the Immune System -HIV viruses infect helper T cells. Can you see why people with AIDS are immune suppressed? -Note what cell is central in both humoral and cell-mediated immunity Autoimmune Diseases -Lupus, rheumatoid arthritis, and multiple sclerosis are examples of autoimmune diseases -In each case, the immune system turns against particular molecules of the body, generating antibodies that attack and damage the body s own healthy cells

ANIMALS FORM & FUNCTION BODY DEFENSES NONSPECIFIC DEFENSES PHYSICAL BARRIERS PHAGOCYTES. Animals Form & Function Activity #4 page 1

ANIMALS FORM & FUNCTION BODY DEFENSES NONSPECIFIC DEFENSES PHYSICAL BARRIERS PHAGOCYTES. Animals Form & Function Activity #4 page 1 AP BIOLOGY ANIMALS FORM & FUNCTION ACTIVITY #4 NAME DATE HOUR BODY DEFENSES NONSPECIFIC DEFENSES PHYSICAL BARRIERS PHAGOCYTES Animals Form & Function Activity #4 page 1 INFLAMMATORY RESPONSE ANTIMICROBIAL