immune system chapter 52 Flashcards
Introduction
Body’s defenses are integrated Innate Immunity—chemical and physical barriers Recognition of invading pathogens Rapid response but not very specific Uses soluble antimicrobial proteins Adaptive immunity Characterized by genetic rearrangements that generate a diverse set of molecules to recognize any invader Slower response but highly specific
Innate immunity
Skin—Largest organ of the body; first line of defense
A. Physical barrier
Provides a nearly impenetrable barrier
B. Chemical barrier
Reinforced with chemical weapons
Oil and sweat glands give skin a pH of 3–5
Lysozyme breaks bacterial cell walls
C. Contains normal flora
Nonpathogenic microorganisms that out-compete pathogenic ones
Tubules with openings to outside lined with mucus which traps microbes and contain macrophages
Digestive tract Mouth—salivary lysozymes acidic stomach Nonpathogenic normal flora Respiratory tract Ciliary action Urogenital tract Acidic urine, normal flora
Binding of a pathogen-associated molecule to any of the innate immune-type receptors activates signal transduction pathways that lead to a rapid response
Cytokines (signaling molecule)
Macrophage binds to PAMP or MAMPsecretes cytokinesbind to receptors on other cellstriggers a response
Interferon—protein secreted by a virus-infected cellmessenger that protects normal uninfected cells
Defensins—bind to pathogen membranedisrupts it
Lysozymes—enzymes in fluids that break down pathogens
3 kinds of defending
leukocytes
Macrophages
Kill microorganisms through phagocytosis
Monocytes mature into macrophages
Neutrophils
Most abundant circulating leukocyte—first to appear at site of damage or infection
Also use phagocytosis
Natural killer cells—virus-infected cells and tumor cells
Do not attack invading cells directly—attach to cell
Release perforins which make a poreother proteins enter and induce apoptosis in target cell
Inflammatory response
Inflammation involves several body systems
Injured cells release chemical alarms, including histamine and prostaglandins
Cause nearby blood vessels to dilate and increase in permeability—neutrophils and monocytes (macrophages)
Promote phagocyte accumulation
Hallmark signs – redness, warmth, swelling (edema), pain, and potential loss of function
Inflammation is accompanied by an acute phase response
One manifestation is fever
Macrophages release interleukin-1
Causes hypothalamus to raise body temperature
Promotes activity of phagocytes, while impeding microbial growth
Causes spleen and liver to sequester iron—bacteria need iron to reproduce and grow
However, very high fevers are hazardous as they may denature critical enzymes
Complement system—complement the immune system
Consists of about 30 different proteins that circulate in the blood in an inactive form
Becomes activated
Proteins aggregate to form a membrane attack complex (MAC) on surface of pathogen
Pathogen swells and bursts
C3b—coats pathogenmacrophage phagocytizes
Stimulates release of histamines inflammatory response
Adaptive immunity
The scientific study of immunity began with Edward Jenner in 1796
Observed that milkmaids who had cowpox rarely experienced smallpox
Inoculated individuals with fluid from cowpox vesicles to protect them from smallpox
Vaccination
An antigen is a molecule (protein) that provokes a specific immune response
May be components of microorganisms or proteins/glycoproteins found on surface of red blood cells or transplanted tissue cells
A single antigen may have many different antigenic determinants or epitopes that makes them specific
Each can stimulate a distinct immune response
Leukocytes are major players in adaptive immunity
Hematopoiesis
All blood cells are derived from hematopoietic stem cells in bone marrow
Lymphoid progenitor gives rise to B and T lymphocytes and natural killer cells
Myeloid progenitor gives rise to all other white blood cells, plus RBCs and platelets
Characterized by
Specificity of recognition of antigen—specific immune cells recognize specific antigens initiates specific immune response
2. Wide diversity of antigens can be specifically recognized
3. Provides immune “memory”, whereby the immune system responds more quickly to an antigen it encountered previously than one it is meeting for the first time
4. Ability to distinguish self-antigens from nonself antigens
Involves:
T and B lymphocytes (T cells and B cells)
MHC (Major Histocompatibility Complex)
Antigen Presenting Cells
Lymphocytes are leukocytes with surface receptors for specific epitopes (antigenic determinants) on an antigen
Direct a specific immune response against either the antigen or the cell that carries it
Although all the receptor proteins on any one lymphocyte have the same epitope specificity, it is rare that any two lymphocytes have identical specificities
When a naive lymphocyte binds a specific foreign antigen for the first time, it gets activated by a process called clonal selection
Produces a clone of cells: some respond immediately and initiate an immune response and others remain as memory cells
B lymphocytes or B cells
Respond to antigens by secreting antibodies or immunoglobulins (Ig)
Participate in humoral immunity
T lymphocytes or T cells
Regulate other immune cells or directly attack cells that carry specific antigens
Participate in cell-mediated immunity
Immunity can be acquired in two ways
Active immunity results from activation of an individual’s own lymphocytes
Pathogen infection or vaccination
Passive immunity results from obtaining another individual’s antibodies
Transfer of maternal antibodies across placenta
Organs of the immune system Primary lymphoid organs Bone marrow and thymus Secondary lymphoid organs Lymph nodes, spleen, and mucosal-associated lymphoid tissue (MALT)
Primary Lymphoid Organs—Bone marrow and thymus
Bone marrow is site of B cell maturation
Each B cell has about 105 Ig (B cell receptors) molecules on its surface
All with the same specificity
All different from cell to cell
Primary Lymphoid Organs
Thymus is the site of T cell maturation
Each T cell has about 105 identical T-cell receptors, or TCRs on its surface
Recognize epitopes only if they are combined with major histocompatibility complex (MHC) peptides
T cells mature before birth and a few months after birth—if thymus removed—no cell-mediated immunity
Secondary Lymphoid Organs—lymph nodes, spleen, MALT, tonsils
Locations of these organs promote the filtering of antigens that enter any part of an individual’s body
Mature but naive B and T cells become activated in the lymph nodes
Spleen is site of immune responses to antigens found mainly in the blood
Mucosal-associated lymphoid tissue (MALT) include the tonsils and appendix
All body cells display self-antigens on the surface—called self-major histocompatibility complex (MHC). This is how cells recognize each other as self rather than a foreign antigen. Your MHC self antigens are different from everyone eWhen macrophages and dendritic cells come into contact with a pathogen, they engulf it and break it down. Peptides of the foreign antigen are displayed with the self-MHC of the macrophage or dendritic cell . The cell then becomes an antigen presenting cell (APC) with a foreign antigen-MHC.
When macrophages and dendritic cells come into contact with a pathogen, they engulf it and break it down. Peptides of the foreign antigen are displayed with the self-MHC of the macrophage or dendritic cell . The cell then becomes an antigen presenting cell (APC) with a foreign antigen-MHC.
When a B cell comes into contact with a pathogen, the pathogen’s (bacteria) epitope binds to the receptor (immunoglobulin) on the B cell membrane. The B cell becomes an APC. The immune system recognizes this foreign antigen-MHC and initiates an immune response.
Cells that can become antigen presenting cells:
Macrophages cell-mediated immunity
Dendritic cells cell-mediated immunity
B cells humoral immunity
Cell-mediated immunity
T lymphocytes are of two types Cytotoxic T cells (Tc) CD8 proteins on cell surface—CD8+ cells Helper T cells (TH) CD4 proteins on cell surface—CD4+ cells
Both are activated by an APC
Cytotoxic T cells
Macrophages and dendritic cells engulf viral-infected cells or tumor cellsbecome APC
Cytotoxic T cells—recognize foreign peptides bound to self-MHC class I proteins on APC
APC activates cytotoxic T cellsClonal expansion and differentiation into activated TC cells and memory cells
Activated T cells induce apoptosis in cells with same specificity as first cell
Helper T cells
Secrete cytokines that promote activation or differentiation of immune system cells—regulatory cells
Naïve TH cell encounters APC in secondary lymphoid organs that has phagocytized a virus-infected cell or cancer cell
TH cell binds to APC and is activated
Activated TH cells give rise to more TH cells and memory cells
Activated TH stimulate macrophages to better phagocytize pathogens and also stimulate TC cells
It is the TH cells and the cytokines they secrete that determine whether an immune response will be cell-mediated or humoral
