Circulating precursor to macrophage. Peanut shaped nucleus with numerous granules in the cytoplasm. MHC II class surface molecules, Fc and complement receptors, and CD14. Highly phagocytic, produce cytokine, and present antigen. "Scavenger cell"
Characteristics of Dendritic Cells
Activate T-cells and initiate adaptive response. Multi-extension cell. High expression of MHC II for antigen presentation.
Characteristics of Neutrophils
Phagocytic and microorganism killing cells. Predominant white cell. Multiple granules/lysosomes. Fc and complement receptors. Short lived and dies with pathogens.
Characteristics of Eosinophils
Kill antibody tagged parasites by releasing granule contents. Also phagocytic. Granules contain "major basic protein" and hydrolytic enzymes. Attack cytotoxic worms and initiate allergic reaction through mast cell activation.
Characteristics of Basophils
Granulocytes that are very few in circulation. Contain histamine, heparin, and proteases. Fc receptors for IgE. Roles in allergic, parasitic, and inflammatory reactions.
Specific Basophils found in CT and ET in high numbers. Have Fc receptor for IgE. Involved in allergic, parasitic, and inflammatory reactions. Contain histamine, heparin, and proteases.
Characteristics of Natural Killer Cells
Larger cells lacking in TCR or immunoglobulin on surface. Have Fc receptor, CD16, and, CD56. Kills virus-infected cells and tumor cells.
Characteristics of gamma:delta T-cells
Low concentration in circulation. Ligand for receptors not well defined. Release cytokines to strengthen immune response in the event of an infection.
What are the cells of the acquired immune system?
T and B lymphocytes representing 20-45% of total wbc's. Most of these are T-cells. Majority are inactive.
What are the two major subsets of T-cells?
CD4 and CD8.
What are CD4 T-cells?
Characteristics of Helper T-cells
Express TCR and CD4. Recognize antigens bound to MHC II and secrete cytokines as a response.
Types of Helper T-cells
TH1: Controls macrophages with IL-2 and IFN-delta TH2: Helps B-cells with IL-4 and IL-5.
What are CD8 T-cells?
Characteristics of Cytotoxic T-cells
Express TCR and CD8 on surface. Recognize MHC I and and induce apoptosis of target cells via granules.
What qualifies as a lymphocyte?
B-cells and both cytotoxic and helper t-cells.
Characteristics of B-cells
Express BCR and MHC II. Able to recognize soluble, unprocessed antigen, and can act as APC. Once activated, differentiates into antibody releasing plasma cell.
What is primary lymphoid tissue?
Where lymphopoesis occurs; where lymphoid cells are produced.
What is secondary lymphoid tissue?
Where immune response is initiated and generated.
What is bone marrow's role in immunity?
WBC's are produced here just like rbc's. Immature cells reside near bone and mature cells exit the central sinus. B-cells fully develop here while T-cell must mature in the thymus.
How is the thymus arranged?
As a bilobed structure with a cortex and medulla. Cortex houses immature thymocytes and mature thymocytes collect in the medulla with macrophages and dendritic cells.
What is the site of negative selection?
What are the immune portions of the spleen?
Periarteriolar lymphoid sheath (PALS) surrounding the arterioles and the Lymphoid follicle, an outpocketing of the PALS.
Where are T-cells in the spleen?
Where are the B-cells in the spleen?
In the lymphoid follicle
What is occurring if there are B-cells on the outer mantle of the lymphoid follicle?
An ongoing infection causing B-cells to proliferate.
What is the role of lymph nodes?
They are fibrous capsules where tissue-borne antigens initiate an immune response.
How is the lymph node arranged?
In follicle, paracortical spaces, and medulla regions.
What cells are localized in lymph node medulla?
Macrophages and plasma cells
What cells are localized in lymph node follicles?
What cells are localized in the paracortical region of lymph nodes?
If there is a cut in the skin leading to antigen invasion, how does the lymph node become involved?
A dendritic cell will capture, process, and present the antigen while traveling to the lymph node. The presentation is recognized in the lymph node and appropriate cells are released into circulation.
What are GALTs?
Gut-associated lymphoid tissues
Where are GALTs?
Tonsils, adenoids, appendix, and Peyer's patches.
How are GALTs organized?
Into B-cell areas, T-cell areas, follicles, and germinal centers.
What happens to activated lymphocytes in GALTs?
They are trapped there, proliferate and differentiate, until infection resolved.
Why do naive immune cells continue to circulate?
They haven't found an antigen to activate them. Once activated they leave the blood for non-immune tissues.
What are cytokines and why are they important?
Small proteins produced by many immune cells to alter self and other cells' behavior. This are the communication system of the immune system. No cytokines = no immune response.
Serum proteins that circulate in pro-enzymatic state. Once activated, can take part in inflammation, opsonization, and damaging microbial cells.
What does clearance of pathogen depend on?
Prompt recognition by APC's and efficient function of effector cells in elimination.
How does tissue injury initiate inflammatory response?
Injured tissues release cytokines which induce capillary dilation. Blood flow increases causing area to become warm and red. Cytokines also recruit inflammatory immune cells which release histamine.
What is prostaglandin?
A mediator of inflammation and an inducer of pain.
What are the processes of innate immune response?
1. Macrophages engulfing pathogen and initiating local inflammatory response 2. Neutrophils and NK cells recruited at site of infection 3. Complements act as molecular tag to enhance response as well as lyse foreign cells.
Characteristics of innate immune response
1. No adaptation to specific antigen 2. Doesn't require time to mount response 3. Responds same way every time 4. Doesn't recognize self and non-self as well as adaptive
When does adaptive immune response occur?
When innate immune response fails.
How are pathogens recognized by T-cells?
How are antigen bound by B-cells?
Ig on B-cell surface
What is an epitope?
Antigenic determinant: antigen bound to TCR or Ig.
How is specificity determined?
Genetically and through variation and reorganization of receptor structure. Leads to highly specific molecules.
What recognizes MHC I?
CD8 / cytotoxic T-cells
What recognizes MHC II?
CD4 / Helper T-cells
What cells present on MHC I?
Cells infected with viruses or certain types of infiltrating bacteria
What types of cells present MHC II?
Cells that take pathogens from extracellular space via endocytosis and phagocytosis and degrade the pathogens into smaller peptides.
What are the different aspects of antibody mediated response?
Neutralization, opsonization, and complement activation
What is neutralization?
When ab's bind a pathogen and inhibit its function, growth, and replication.
What is opsonization?
IgG coat the surface of a pathogen and facilitates phagocytosis.
What is complement activation?
Ab's are recognized by complement which opsonize the pathogen and help phagocytosis.
What is positive selection?
When T-cells are selected for their ability to bind antigen.
What is negative selection?
When T-cells are selected out for their ability to bind self or too tightly bind an antigen.
What is the principle of vaccination strategy?
That secondary response is quicker and of greater intensity than primary response.
What does it mean for the immune response to be diverse and specific?
Our body can recognize multiple antigens at the same time with varying degrees of response for each antigen.
Characteristics of adaptive immunity
1. Adaptive to specific antigen 2. Slower to develop 3. Specific response for specific antigen 4. Repeat encounters yield faster responses 5. High discrimination for self and non-self 6. Diverse
What happens the first time an allergen is encountered?
Nothing. Mast cells bind the allergen tagged by IgE on secondary exposure and cause an emptying of granules containing histamine, leukotreins, and bradykinins which induce an anaphylactic response.
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