Lecture 16 Flashcards
Immunity
Acquired resistance to an infectious agent due to prior contact with that agent
Humoral immunity
Also known as antibody-mediated immunity, antibodies in all fluids, involves B lymphocytes both plasma and memory cells, effective against extracellular pathogens
Cell-mediated immunity
Involves T lymphocytes both T helper cells and cytotoxic T cells as well as memory cells, uses contact-dependent signaling, defends against intracellular pathogens
Allergens
Antigen typically not harmful to the body but can produce an inappropriate immune response to sensitive people
Antibody (Ab)
Protein molecules produced by B cells that recognize specific antigens and help destroy them
Also called immunoglobulins
Antigenic determinant or epitope
Precise portion of an antigen that is recognized and bound by an antibody
Opsonins
Proteins that coat pathogens so that phagocytes recognize and ingest them
Phagocytes WBCs
Macrophages, neutrophils, and eosinophils
Antigen
Any molecule that can trigger an immune response
Antigens
Stimulate a response to B and T cells, larger more complex structures make better antigens and are easier for antibodies to recognize and bond, smaller repetitive structures are poor antigens may not stimulate an immune response
Antibody structure
Made by plasma B cells in response to an antigen, made of 4 polypeptide chains 2 light chains and 2 heavy chains, chains bound together by disulfide bonds, constant regions on both chains determine the specific class of antibody
Antibodies of the same class
Have identical constant regions
Variable regions
Antibody tips are composed of highly variable amino acid sequences, provides specificity to bind to antigen
Antibody tips
Create 2 antigen binding sites
Antigen arms
Antigen binding fragments (Fabs)
Rest of antibody
Crystallizable fragment (Fc)
Complement binding site
On antibodies that do classical pathway of activating complement proteins
IgG
Crosses placenta and fixes complement, most abundant antibody 80% , if high in these but low in IgM towards end of infection, long term memory immunity
IgA
Found in body fluid secretions near portals of entry with mucus, secretory antibody
IgM
First antibody ever made when you first come into contact with antigen, don’t last long, high IgM newly infected, can serve as B cell receptor, fixes complement
IgD
Known as B cell receptor on B en surface
IgE
Antibody of allergy and worm infections
Antibody functions
Neutralization- by surrounding and blocking receptors from binding cells on pathogens and toxins
Complement fixation
Agglutination- cross link bacteria making it difficult for them to move and infect so macrophage can bind Fc and eat
Opsonizes bacteria to surrounds to make more enticing for macrophages
B cell receptor
IgD antibody attached to the B cell surface, the receptor on each cell is specific to a particular antigen
Colonal selection
Lymph fluid passes over B cells in lymph nodes and lymph tissues as they look for antigens, when an antigen is found the B cell with the matching B cell receptor binds the antigen and becomes activated
B cell differentiation
Once activated the B cell differentiates into memory and plasma cells
Colonal expansion
After differentiating the been undergoes many divisions giving rise to plasma and memory cells
Plasma cells
Secrete lots of antibodies IgM with the same specificity as the original B cell receptor
IgD becomes IgM
Memory cells
Produce IgG, these cells remain for long periods in lymph nodes to react with the same antigen at a later time
Order of antibody response
Colonel selection and differentiation, IgM first, IgG to create memory
Second exposure: quickly makes lots of IgG and some IgM
Making the B cell receptor
Exons from immunoglobulin genes are randomly selected during the development of each B cell, each one is unique in its antigen specificity
Colonal deletion
Eliminate clones with receptor that have a specificity for self molecules
MHC also called
HLA human leukocyte antigen
Class I MHC
Cytotoxic T cells bind to MHC I via their T cell receptor and CD8 molecules, present intracellular antigens and cellular molecules, all cells except RBCs
Class II MHC
Made and presented by professional antigen presenting cells, presents bits of digested foreign antigens, T helper cells bind MHC II via their T cell receptor and CD4 molecule
T helper I cells
Stimulate macrophages, activate nearby cytotoxic T cells and other T helper cells
T helper II cell
Stimulate B cells and suppress T helper I cells
CD4+ T memory cells
Helper cells create memory
T cell receptor components
Bind specifically to both a particular antigen and the self-MHC presenting antigen
Clusters of differentiation CD
Additional receptors on T lymphocytes use to identify cytotoxic T cells and T helper cells
Cytotoxic T cells
CD8+ cans that interact with MHC I receptors they destroy foreign or abnormal cells and give rise to CD8+ T memory cells
Negative selection
T cells with useless or dangerous TCRs are destroyed
Positive selection
T cells with good TCRs are propagated and sent on to the lymph nodes and lymphoid tissue all over the body
Antigen presenting cells
Dendritic, macrophages and B cells
Present foreign antigens on MHC II to the correct T helper cells
T-helper cell 1 activation
Binding of MHC II of macrophage or dendritic cell to TCR and CD4 is the first step of T helper cell activation
Macrophage or dendritic cell release Interleukin I: signals T helper cell to become type 1
T helper 1 releases IL-2 the most powerful human immune system stimulator which activates cytotoxic T cells, turns monocytes into macrophages, activates more t-helper cells which release more IL-2
T helper cell 2 activation
MHC II of B cell with foreign antigen binds TCR and CD4, B cell releases IL-4
IL-4 signals T helper cell to become t helper cell 2
Th2 cue releases IL-4 and B cell growth factor causing colonal expansion of B cell
Differentiates and expands to many memory and plasma cells
Memory cells go onto create IgM
Plasma cells make IgG
Cytokines
Chemical messenger molecules that communicate between immune cells
Includes IL-1, IL-2, IL-4, interferons, chemokines
Interferon
Cytokine released by virally-infected cells that stimulates production of anti-viral proteins
Chemokines
Cytokine released by mast cells that attracts leukocytes to an infection
Cytotoxic T cell activation
TCR on cytotoxic T cell and CD8 bind to a particular antigen on MHC - I
Stimulated by IL-2 from TH1 cells
Activated cytotoxic T cells release perforins and granzymes which enter and degrade infected host cell proteins
Graft rejection
Cytotoxic T cell mediated immunity is most important factor,Tc cells recognize abnormal MHC I and mark cells for destruction
T helpers specific to
Interact only with MHC II so specifically activated by APCs only
Conductors of the entire immune system
T c cells specific to
Interact with MHC I they can be activated by any cell of the body so they can target and destroy cells with viral infection and cancerous cells
B cells
Extracellular antigens/free floating/humoral
T cells
Cell-mediated/ intracellular pathogens on surface of infected cell or APC
