MMG Specific Defenses

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What triggers specific immune responses in the body?: -antigens
What forms can antigens take?: -bacterial cell walls
-capsules
-pili
-flagella
-viruses
-fungi
-protozoa
How do antigens enter the body?: -breaks in the skin (and mucous membranes)
-direct injection (as with a bite or needle)
-organ transplants (and skin grafts)
What does the lymphatic system do?: -to screen the tissues of the body for foriegn antigens
What do lymphatic vessels do?: -form a one-way system that conducts lymph from local tissues and returns it to the circulatory system
What is lymph?: -liquid with similar composition to blood plasma that arises from fluid leaked from blood vessels into surrounding tissues
Where do lymphoid cells develop?: -stem cells
-red bone marrow
What designates B and T lymphocytes?: -glycoprotein found on surface
ie: CD4, CD8
Where do B cells mature? T cells?: B=bone marrow
T=thymus
Where are B-cells found?: -spleen, lymph nodes, red bone marrow, and Peyer's Patches
*small percentage circulating in blood
What is the major function of B cells?: -secrete antibodies such as immunoglobulins
What is the humoral immune response?: -body fluid immunity (such as lymph and blood)
What are antigen-binding sites?: -complementary to antigenic determinants (epitopes)
-form strong, noncovalent interactions
-Hydrogen bonds and other attractions may also be involved
What are 6 antibody functions?: -activation of complement
-stimulation of inflammation
-agglutination
-neutralization
-opsonization
-antibody-dependent cell mediated cytotoxicity
What is agglutination?: -each antibody has 2 antigen binding sites
-binding of multiple antibodies can lead to clumping or agglutination
What is neutralization?: -binding to toxin or cell, thereby blocking active sites or adherence to target cells
What is opsonization?: -AKA enhanced phagocytosis
-phagocytes have receptors that recognize parts of antibodies
-coating of antigen with antibodies
What is antibody-dependent cell mediated cytotoxicity?: -attachment of antibody to target cell leads to lysis by non-specific immune cell
What does antibody classification depend on?: -type of foreign antigen
-portal of entry
-antibody function needed
What are 5 antibodies?: -IgG
-IgM
-IgA
-IgE
-IgD
What is the function of IgG?: -complement activation, agglutination, opsonization, and neurtralization
-crosses placenta to protect fetus
-85% in serum
What is IgM?: -complement activation, agglutination, and neutralization
What is IgA?: -Agglutination and neutralization
What is IgE?: -Triggers release of histamines from basophil mast cells
What is IgD?: -unknown
What antibody is the only non-monomer (pentamer)? How about a dimer?: -IgM
-IgA (also a monomer)
What is a B-cell receptor (BCR)?: -antibody molecule that remains attached to cytoplasmic membrane of B cells
-complementary to only one antigenic determinant
Where are T-cells found?: -circulate in lymph and blood
-migrate to lymph nodes, spleen, and Peyer's patches
How do T-cells work?: -in a cell-mediated immune response (no antibody secretion, act directly on:)
-endogenous invaders
-many of the body's cells that harbor intracellular pathogens
-abnormal host cells that produce abnormal surface proteins (cancer cells)
What are the three types of T-cells?: -Cytotoxic T cells
-2 Types of helper T cells
Describe Cytotoxic C cells (Tc)?: -contain hundreds of T cell receptors (TCR)
-distinguished by the CD8 cell-surface glycoprotein
-directly kills
What do Tc cells kill directly?: -cells infected with viruses and other intracellular pathogens
-abnormal cells, such as cancer cells
What distinquishes Helper T cells (TH)?: -CD4 cell-surface glycoprotein (this is what HIV binds to)
What is the function of Helper T cells?: -help regulate the activities of B cells and cytotoxic T cells during an immune response
-secrete various soluble protein messengers, called cytokines, that determine which immune response will be activated
What are the two types of helper T cells?: -Type 1 (TH1)
-Type 2(TH2)
What do Type 1 helper T cell do?: -assist cytotoxic T cells
-express cytokine reveptor CCR5- plays a role in binding of HIV!!
What do Type 2 helper T cells do?: -Activate B cells to make and secrete antibodies
-have cytokine receptors CCR3 and CCR4
What are cytokines?: -soluble regulatory polypeptides that act as intercellular signals when released from certain body cells
What is the cytokine network?: -the complex web of signals among all the cell types of teh immune system
What are 5 types of cytokines?: -interleukins (ILs)
-interferons (IFNs)
-growth factors
-tumor necrosis factors (TNFs)
-chemokines
What do interleukins do? interferons?: -signal among leukocytes (27 to date)
-antiviral proteins that may act as cytokines
What do growth factors do as cytokines?: -proteins that stumulate stem cells to divide, maintaining an adequate supply of leukocytes
What are Tumor necrosis factors?: -secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation
What are chemokines?: -signal leukocytes to go to a site of inflammation or infection and stimulate other leukocytes
What are MHC antigens?: -glycoproteins found in the membranes of most cells of vertebrate animals
When were MHC antigens first identified? Why are they important?: -first identified in graft patients
-important in determining the compatibility of tissues in successful grafting
What is the function of MHC antigens?: -to hold and position antigenic determinants for presentation to T cells
Where do antigens bind to the MHC?: -antigen-binding groove
What are the two classes of MHC proteins?: -MHC class I; found in most membranes
-MHC class II; only found on B cells and antigen-presenting cells (macrophages, leukocytes, monocytes)
What are exogenous antigens?: -extracellular pathogens such as bacteria, fungi, protozoa
What does APC do?: -internalizes the invading pathogen and enxymatically digests it into smaller antigenic fragments which are contained within a phagolysosome
What happens to the phagolysosome after pathogen is digested?: -fuses with a vesicle containing MHCII molecules
What happens to each fragment from the phagolysosome?: -binds to the antigen-binding groove of a complementary MHCII molecule
What happens to the vesicle once it fuses with phagolysosome: -vesicle inserts the MHCII-antigen complex into the cytoplasmic membrane so the antigen is presented on the outside of the cell
What are endogenous antigens?: -intracellular pathogens such as viruses and bacteria
What happens in endogenous antigen processing?: -intracellular pathogens also digested and each fragment binds to a MHCI molecule (in ER membrane)
-membrane packaged into vesicle by Golgi body which is inserted into cytoplasmic membrane so antigen is displayed on cell's surface
How does the body respond to exogenous pathogens?: -by mounting humoral immune responses
What is the first step in humoral immune responses?: -APC presents antigen to complementary Th cell
-CD4 binds to MHC II protein, stabilizing the TCR-antigen interaction
What is the second step in humoral immune responses?: -TH cell differenetiates into a TH2 cell, cuased by IL-1 secreted by APC
What is the third step in humoral immune responses?: -TH2 cell binds to B cell that contains a BCR complementary to antigen (clonal selection)
What is the fourth step in humoral immune responses?: -the B cell MHCII binds to CD4 of TH2 cell, which leads to IL-4 secretion
-then activation of B cell proliferation into plasma cells, which produce antibodies, and memory B cells
What do Cytotoxic T cells respond to?: -intracellular pathogens (viruses, intracellular bacteria) and abnormal body cells
What is the first step in the TC cell-mediated immune response?: -viral-encoded antigens are presented via MHC I complex
What is step two in the Tc cell mediated immune response?: -TCR and CD8 of Tc cell bind to MHC I-antigen complex
What is step three in teh Tc cell mediated immune response?: -either perforin-granzyme pathway or CD95 pathway is activated, leading to induction of enzymes that cause apoptosis (programmed cell death)
How are T cells regulated?: -cell-mediated immune response must be regulated to prevent T cells from responding to autoantigens
-T cells require additional signals from APC to an immunological synapse to stimulate the T cell response to the antigen
What are 6 ways microbes can evade immune systems?: -capsules
-LPS modifications (O antigen)
-Enzymes that degrade C5a
-Proteases
-Surviving phagocytosis
-Antigenic variation
How do capsules help microbes evade detection from the immune system?: -prevents complement activation and phagocytic killing:
1) C3bBb formation on surface inhibited
2) phagocyte receptors can't reach
3) nonimmunogenic; no opsonization for phagocytes
What are the two ways LPS modifications work?: -different side chains prevent complement activation
-different side chain lengths prevent MAC formation
How do proteases help in immune system evading?: -specifically degrade antibodies
What is used for enzymes that degrade C5a in immune system evading?: -phagocyte chemoattractant

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