Chapter 35 The Body’s Defenses

35.1 The Lymphatic System l plasma leaves the blood at capillaries  carries food and picks up waste  this fluid fills space between cells—called interstitial fluid  needs to be returned to the blood l lymph system is a series of tubes (lymphatic vessels) that return interstitial fluid to the blood  fluid in lymph vessels is called lymph  plasma, interstitial fluid, and lymph are the same juice, different place

Human Lymphatic System

The body’s defenses

35.2 Nonspecific and Specific Defenses Nonspecific defenses occur automatically and have no memory l 1. barriers to entry  skin  mucous membranes  secretions (oil, lysozyme, acid in stomach) l 2. inflammatory response: caused by physical or chemical damage or pathogens  outward signs (from capillary changes) redness heat swelling pain

Cilia in trachea

35.2 Nonspecific and Specific Defenses l 2. inflammatory response, cont.  helps prevent spread of infection can inhibit healing if skin is not broken (ice, ibuprofen, cortisone)  triggered by damaged tissue cells and mast cells (WBCs in connective tissues) releasing histamine results in dilation of vessels increased permeability  also triggers fever inhibitis microbes helps in tissue repair facilitates phagocytes faster immune cell division

Fig Inflammatory response

Inflammatory response

35.2 Nonspecific and Specific Defenses l 3. phagocytes and natural killer cells  phagocytes neutrophils and monocytes: amoeboid, squeeze through capillaries  monocytes become macrophages dendritic cells (in skin, mucous membranes) and macrophages (other tissues)  recognize pathogens with receptors  devour pathogens  release cytokines to stimulate neutrophils and monocytes  move through tissue fluid  lymph  spleen and activate B and T cells

Phagocytosis

35.2 Nonspecific and Specific Defenses l 3. phagocytes and natural killer cells  natural killer cells (NK) large, granular kill infected (viral) and cancerous body cells by cell-cell contact kill cells without self-proteins; same manner as cytotoxic T cells

35.2 Nonspecific and Specific Defenses l 4. protective proteins  complement (blood plasma proteins) amplify inflammatory response can bind to pathogens with antibodies, ensuring phagocytosis can form membrane attack complex; holes cause lysis  interferons produced by virus-infected cells to warn others cause production of substances that interfere with viral replication in non-infected cells

35.2 Nonspecific and Specific Defenses Specific defenses require B-cells and T-cells l two major cell types:  B cell lymphocytes chemical immunity, kill germs using chemicals (antibodies) made in Bone marrow  T cells lymphocytes helper T: control immune system (T H ) cytotoxic T: kills germs (T C ) suppresser T: stops immune system when the attack is over (T S ) made in Thymus

35.2 Nonspecific and Specific Defenses l two major cell types, cont.  lymphocytes respond to antigens antigen (“antibody generating”): foreign molecule (protein) that elicits a response by lymphocytes may belong to viruses, bacteria, fungi, protozoa, parasitic worms, pollen, transplanted tissue, etc.  stimulate production of antibodies, which bind to antigens  B cells and T cells undergo clonal selection there are millions of types of lymphocytes, each with unique membrane receptors specific for various antigenic molecules

Clonal selection

35.2 Nonspecific and Specific Defenses l two major cell types, cont.  B cells and T cells undergo clonal selection when an antigen is encountered for the first time, the lymphocyte attaches to the receptor complementary to it cell with the receptor produces clones of itself; clones become:  effector cells (plasma cells)—attack the antigen (primary immune response (takes days))  memory cells (last a lifetime)—quickly attack antigen on 2nd (and later) exposures (secondary immune response, AKA immunity)

35.2 Nonspecific and Specific Defenses l two major cell types, cont.  lymphocytes work by recognizing each other, invaders, and other body cells with proteins on their membranes major histocompatibility complex (MHC)  Class I MHC: on all body cells, identifies cells as being part of the body  Class II MHC: only on immune cells  antigens attach to MHC proteins B cells have antigen-specific receptors (similar to antibodies) on their membranes T cells have T cell receptors on theirs both types of receptors are complementary to a specific antigen/MHC

Interaction of T cells with MHC molecules

Specific defenses flow chart

35.2 Nonspecific and Specific Defenses l helper T cells (T H )  immature T H becomes a mature T H  T H divides producing clones and memory T H  stimulate B and T C

Role of helper T cells

35.2 Nonspecific and Specific Defenses l role of T H cells  macrophage surrounds and engulfs antigen  macrophage begins to “process” the antigen  processed antigen will be attached to Class II MHC

35.2 Nonspecific and Specific Defenses l role of T H cells, cont.  processed antigen on the macrophage is complementary to T H receptor  T H and macrophage bind  interleukins are released by the macrophage which causes T H to mature

35.2 Nonspecific and Specific Defenses l cell-mediated immunity  uses cells (T C ) to kill eukaryotic cells, including: protists and fungi, virus-infected cells, cancer cells  steps (for instance): antigen enters a body cell and is processed after being processed, the antigen is displayed on a Class I MHC

35.2 Nonspecific and Specific Defenses l cell-mediated immunity  steps, cont. immature cytotoxic T cell binds with macrophage displaying antigen mature helper T-cell attaches to Class II MHC on macrophage and pumps out interleukins

35.2 Nonspecific and Specific Defenses l cell-mediated immunity  steps, cont. interleukins cause cytotoxic T cell to mature mature T C binds to infected cell and pumps out perforin to kill it

Perforin

35.2 Nonspecific and Specific Defenses l antibody-mediated immunity  kills bacteria and viruses with antibodies  antibodies: cause germs to stick together or precipitate, easier for macrophages to eat inactivate germ (block virus attachment) work with the complement proteins to kill the germ are made by B cell lymphocytes

Antibody activity

35.2 Nonspecific and Specific Defenses l antibody-mediated immunity  steps: a specific B cell binds to an antigen (such as a virus) by its receptor antigen is engulfed antigen is processed and the processed antigen is displayed on the Class II MHC

35.2 Nonspecific and Specific Defenses l antibody-mediated immunity  steps, cont. B cell is now activated and finds a mature helper T cell, usually at a lymph node or other lymphatic tissue helper T cell releases interleukins which cause B cell to divide

35.2 Nonspecific and Specific Defenses l antibody-mediated immunity  steps, cont. new B cells are called plasma cells which mass produce antibodies (30,000 molecules/second!) some B cells become memory cells which wait until next infection (source of immunity)

Immunological memory

AIDS l human immunodeficiency virus attacks helper T cells l antibodies are made, but are ineffective l HIV stays dormant for awhile (lysogeny) until some secondary infection strikes l helper T cells are quickly killed as HIV spreads, victim loses immunity

Course of HIV-AIDS

Review of specific immunity