The Immune System

Protects our bodies from pathogens – disease causing agents May be bacteria, viruses, protists, fungi, etc Response could be nonspecific or specific to the pathogen

Nonspecific Responses (Innate Immunity) Barrier defenses - cover and line surfaces First line of defense Skin, mucous membranes, tears Also includes antimicrobial lysozyme found in saliva

Cellular innate defenses Combats those that get through the skin/membranes Phagocytic WBCs – “eat” pathogens Neutrophils – ingest and destroy microbes Monocytes  macrophages – giant phagocytes Eosinophils – fight against parasites Antimicrobial proteins Interferons – warn nearby cells of viruses in order to inhibit viral replication Complement – about 30 proteins with variety of functions

Inflammatory Response Triggered by damage to tissue Leads to release of chemical signals Includes histamines from basophils and mast cells (WBCs) Causes dilation of blood vessels Aids in delivery of clotting agents and phagocytes Results in redness, swelling, pain and fever Natural Killer cells (NKs) – help recognize and remove diseased cells

Inflammatory Response

Specific Defenses (Acquired Immunity) Involves pathogen-specific lymphocytes B cells – develop in bone marrow T cells – mature in the thymus Both circulate in blood and lymph Antigens – foreign molecules that elicit a response B and T cells recognize them by specific receptors in their membrane

Humoral Immunity Involves activation of B cells B cells bind to specific antigens and become activated by helper T cells (secrete cytokines) B cells divide into plasma cells which produce antibodies and memory B cells Antibodies prevent the pathogen from infecting cells (neutralization), tag it to be eaten by phagocytes, or activate the complement system causing it to lyse Memory cells respond in future invasions

Antibodies

Humoral Immunity

Cell-mediated Immunity Involves the activation of T cells Helper T cells – activate B cells and cytotoxic T cells Cytotoxic T cells – destroy infected body cells or cancer cells T cells bind to antigens that are displayed by antigen-presenting cells on their MHCs Major histocompatibility complex molecules Differs in individuals due to genes

Immune Response

Immunity Primary response – occurs after first exposure Secondary response – occurs when antigen is encountered again Much faster and stronger due to memory cells Active immunity – develops naturally in response to infection or due to immunization Passive immunity – when an individual receives antibodies Mother to fetus or infant

Diseases Allergies – antibodies to common molecules cause the cells to release histamine and other mediators creating allergy symptoms Autoimmune diseases – the immune system turns against particular molecules of the body Rheumatoid arthritis and multiple sclerosis HIV – infects helper T cells HIV Drop in WBC count leads to AIDS in which body is susceptible to many illnesses