Presentation on theme: "The Body’s Defenses. Nonspecific Defenses Animals need way to protect against disease. 3 lines of defense; 2 nonspecific (don’t distinguish) 1 is specific."— Presentation transcript:
The Body’s Defenses
Nonspecific Defenses Animals need way to protect against disease. 3 lines of defense; 2 nonspecific (don’t distinguish) 1 is specific.
1 st nonspecific disease - external (skin). 2 nd internal (phagocytes) 3 rd immune system. Microbe must get past 1 st line (mucous and skin) to get to 2 nd line (inflammatory response).
Skin intact, act as barrier. Little bit of opening can allow pathogens to enter. All mucous membranes act as barriers. Mucous membranes secrete enzymes to fight off intruders. Cilia in respiratory tract help move trapped organisms out of system up trachea.
Tears contain lysozyme - enzyme that digests peptidoglycan cell walls of some bacteria. Acid in stomach acts as protection.
If microbe gets past defenses, moves to 2 nd line of defense - depends on phagocytosis - ingestion of invading organisms by certain types of white cells.
Variety of proteins function in nonspecific defense by attacking microbes directly or impeding reproduction. Complement proteins - work together to create pore through bacterial membrane - causes cell to burst.
Phagocytes (neutrophils and macrophages) WBCs that non- specifically seek out, ingest infectious invaders through phagocytosis.
Defense against infection - organisms that live in body. Microorganisms found in human body (digestive tract), like E. coli. Advantages to humans for having organisms in body. Compete with other infectious organisms for space.
Taking antibiotics kills bad bacteria, also kills bacteria found in body naturally.
Specific immunity Body also has specific immune responses - occurs when body is invaded by specific organisms, uses B and T cells (white blood cells) to recognize and destroy foreign invaders. B and T cells - lymphocytes.
Self from non-self B and T cells tested to see if self- destruct while still developing. Potential problems removed leaving those who react to foreign invaders, not themselves. Prevents body from attacking itself and only attack foreign invaders.
Lymphocytes exhibit specificity - respond to specific antigens (foreign materials). B or T cell responds to specific antigen from pathogen. B cell response - humoral response; T cell - cellular response.
B cells respond to antigen by making antibodies - proteins (immunoglobulins) that recognize and bind to specific antigens. Antibodies relatively same in structure; 1 end - constant region, other end - variable region (part that differs)
5 different classes of antibodies that perform different immune functions. IgA, IgM, IgE, IgG, and IgD (determined by constant region). IgM 1 st one expressed during infection; found on t surface of B cells (along with IgD).
IgG - largest class in body. IgE - involved in allergic reactions. IgA secreted from body linings like mucous membranes.
Antibodies must recognize huge range of potential antigens found in pathogens (bacteria, viruses) but not recognize proteins produced by organism. Antibodies - complex proteins assembled from multiple polypeptides joined by disulfide bridges between light and heavy chains.
Variable regions of antibodies bind antigens including portions of both light and heavy chains that fold together in complete antibody molecule. During development of B cell, immunoglobulin goes through specific recombination of genes; allows for limitless possible options; each B cell has unique expression.
Cells have same genomic information, not true in B cells. B cells that have immunoglobulins that recognize proteins produced by self are destroyed so that they won’t attack body.
Bacterial infection occurs, B cells that bind to bacterial antigens will replicate - produce 2 types of B cells: plasma cells and memory cells.
Plasma cells - antibody production factories which produce and secrete large amounts of antibodies into blood until after they die. Antibody cleared after couple of days. Short lived but powerful responses.
Memory cells do not express antibodies, stay in circulation for years with immunoglobulin expression for that bacteria on surface. If same (or related) pathogen invades again, memory cells recognize it and provide rapid response, replicating and producing new plasma cells.
Memory cells responsible for effectiveness of vaccines.
T cells play different role in specific response - 2 different types of T cells. Cytotoxic T cells kill cells infected by pathogen that T cell recognizes. Helper T cells coordinate immune response of other cells against specific antigens.
T cells produce wide range of proteins with antigen specificity - not secreted. Expressed by T cell receptors found in membrane of T cells. Recognizes antigen on surface of other cells in specific context, not antigens in solution.
Antigen stimulation - T cell receptor must be presented to cell as part of complex of proteins - major histocompatibility complex (MPH) or human leukocyte antigens (HLA) - found in plasma membrane of cells. 2 types of MHC involved in T cell response, MHC Class I and MHC Class II.
MHC I present on surface of all cells; MHC II a present on immune cells (macrophages, B cells, T cells). MHC present antigen from inside cell at cell surface - T cells can recognize it. T cell receptor of cytotoxic T cell must recognize antigen presented in MHC I on surface of infected cell.
If this happens, cytotoxic T cell will replicate. Future interactions of cytotoxic T cells with infected cell will cause cytotoxic T cell to kill infected cell.
T cells involved in response of B cells to antigen. Helper T cells needed for B cells to respond to antigen. Macrophages will digest antigen and present it in MHC Class II at cell surface. Helper T cells with T cell receptors that recognize antigen will be stimulated.
Replicate and stimulate B cells that respond to antigen to replicated into plasma cells. Many cytokines (proteins or peptides that stimulate other lymphocytes) secreted by helper T cells to communicate with other cells to coordinate immune system.
MHC variable in humans and need to match between donor and recipient in an organ transplant.
Major histocompatibility complex (MHC) is responsible for stimulating rejection of tissue grafts and organ transplants. Minimize rejection, attempts are made to match MCH of tissue donor and recipient as closely as possible.
Prior to transplant, recipient is typically treated with irradiation to eliminate recipient’s immune system, leaving little chance of graft rejection. Donated marrow, containing lymphocytes, may react against recipient, producing graft versus host reaction, unless well matched.
Person must still take drugs to help not reject transplant that leave them open to disease and cancers. Bone marrow transplants - graft itself, rather than host, source of potential immune rejection.
Immunity in health and disease Active immunity (chicken pox) result of individual’s immune system already exposed to disease - can be acquired naturally or by vaccination. Vaccinated person who encounters actual pathogen will have same quick secondary response based on memory cells as person who had disease.
Immunity can be transferred passively. IgG antibodies passed via placenta, IgA antibodies passed in breastmilk. Passive immunity occurs when animal passes (through injection) their immunity to another.
Abnormal immune function Abnormal immune function can result in anything from allergies to autoimmune disease. Allergies are abnormal reaction to allergens (environmental antigens).
Most common allergies - antibodies of IgE class. Hay fever occurs when plasma cells secrete IgE specific for pollen allergens.
Widespread, more dangerous - anaphylactic shock, life-threatening reaction to injected or ingested allergens. Anaphylactic shock results when widespread mast cell degranulation triggers dilation of peripheral blood vessels, causes precipitous drop in blood pressure.
Sometimes body loses tolerance for itself, starts attack on itself - causes autoimmune disease (i.e. rheumatoid arthritis) SCID (severe combined immunodeficiency) - function of both humoral and cell-mediated immune defense compromised.
AIDS AIDS (acquired immunodeficiency syndrome) became well-known. HIV virus (human immunodeficiency virus) - retrovirus that causes AIDS. Mortality for AIDS - 100% - one of the most lethal pathogens.
Once inside cell, HIV RNA reverse- transcribed - product DNA integrated into host genome. Significant loss in humoral and cell- mediated immunity. Decline in helper T cells primarily caused by direct mortality from HIV infection.