Vishy -Intro to Host defenses Flashcards
What are the two main functions of the immune system
- Distinguish self from non self
2. Protect the body from invading infectious organisms (parasites, bacteria, fungi, and virus)
The important components of the immune system include:
- innate immunity
2. adaptive immunity
What are characteristics of innate immunity
- Preformed (already in our body)
- Not specific (can kill a wide range of organisms)
- Lacks immunological memory
- Innate immunity does not improve over time
- Often unsuccessful in controlling the infection and hence adaptive immunity kicks in.
what are components of innate immunity
- barriers like skin and mucous membrane
- neutrophils, monocytes, macrophages, dendritic cells and natural killer cells
- antimicrobial peptides and proteins like complement and C-reactive proteins
what are characteristics of adaptive immunity
- the onset is slow
- once active its highly effective
- adaptive immunity is highly specific to a particular organism
- improves over time
- has immunological memory
Natural killer cells are ___ phagocytic
non
what are components of adaptive immunity
- B lymphocytes
2. T lymphocytes
B lymphocytes differentiate in bone marrow and produce ____ or Ig
antibodies; protein molecules that bind to antigens and neutralize the effects of antigens.
T lymphocytes differentiate in thymus and produce ____ or interleukins
cytokines; dont bind to antigens but activate or suppress the cells of innate and adaptive immunity
what are characteristics of neutrophils and what role do they play
- multilobed nuclei
- phagocytose and kill the organisms intracellularly.
- Have a short life
What are characteristics of monocytes and what role do they play
- kidney shaped nuclei
- phagocytose
- leave circulatory system and migrate to diff organs where they differentiate to macrophages
what are macrophages
differentiated forms of monocytes and have a longer life span (months to years)
what are characteristics of dendritic cells and what role do they play in innate immunity
- similar to macrophages
2. long membrane extensions and are capable of both phagocytosis and pinocytosis
Dendritic cells and macrophages can present the antigens to ___ lymphocytes for recognition and initiate ____ immune responses.
T; adaptive
Monocytse present in ____macrophages are present in _____
circulation; tissue
DCs and macrophages express a unique protein antigen on their cell surface called ____
CD14;
_____ are considered to be the most efficient antigen presenting cells
DC’s; capable of ingesting protein antigens and breaking protein antigens into small antigenic peptides and present it to T cells for recognition
What are the diff classes of MHC
Class 1, II, and III
T cells cannot recognize the protein antigens in their ___state, thats why dendritic cells and macrophages within the intracellular compartment internalize the protein antigensand break them down into simple antigenic peptides which then conjugate with ____ molecule and then present on the cell surface for recognition by T cells.
native; MHC
what are MHC class molecules?
self antigens similar to blood group antigens.
T cells can only recognize processed antigenic peptides expressed in conjunction with either MHC class ____ or ____ molecules on the cell surface of dendritic cells.
I, II
Intracellular killing of phagocytosed microbes by monocytes and neutrophils generates:
- reactive oxygen intermediates
- reactive nitrogen intermediates
- generation of antimicrobial peptides
- fusion between phagosome containing microbes with lysosome
what are the antimicrobial peptides
- lactoferrin: sequesters iron; limits the availability of free iron leading to the death of the pathogen due to iron starvation
- defensins: cationic peptides
- Lysozyme
what are the two types of defensins
- alpha defensins: produced by neutrophils and Paneth cells (stomach)
- beta defensins: epithelial cells in the respiratory tract
what are defensins
positively charged molecules and hence they are cationic proteins and they bind to negatively charged bacterial surface and induce lysis of the bacterial cell.
what is lysozyme
protein present in lysosomal compartment. Degrades peptidoglycan (cell wall component in gram + bacteria)
what are complements
a group of serum proteins that get activated (usually inactive) when there is immune complex formation as a result of antigen antibody reaction or when there is infection with gram negative bacteria.
when does complement activation occur
when there is:
- antigen antibody reactions
- infection with gram negative bacteria causing release of LPS
- Release of mannose (carbs) during fungal or gram + bacterial infection.
what are the two pathways complement can get activated by
- Classical pathway
2. alternate pathway
describe the classical pathway
- antigen antibody reactions result in activation of C1 –>C4 –>C2
- C142 activates C3 which results in activation of C5-9
- C6-9 complex binds to bacterial cell surface causing lysis of the bacteria.
describe alternate pathway
- infections with gram neg bacteria result in the release of LPS.
- LPS directly activates C3 foll by activation of C5-9 and lysis of bacterial cells.
Describe the mannose lectin pathway
Release of mannose activates C4 –>C2.
- C42 activates C3.
- C3 activates other complement factors and formation of membrane attack complex.
Mannose lectin pathway contributes to _____ immunity
innate
what is opsonisation
when the bacterial cell surface binds to the corresponding receptors on the macrophage cell surface resulting in easy and enhanced uptake of the bacteria.
What are characteristics of natural killer cells
- do not attack microbes
2. large granular lymphocytes that lyse the abnormal cells such as cancer cells and microbe infected cells.
what activates natural killer cells
down regulation of MHC Class 1 molecules on leukocyte cell surface will activate NK cells to induce lysis of target cells such as cancer cells or infected cells.
what is the mechanism of NK cells
they produce antimicrobial peptides such as perforin and granulysin. Perforin creates pores on the cell surface of the target cells thereby fascilitating the entry of granulysin into the target cells. Granulysin kills the target cells and the intracellular microbe.
How do innate immunity cells recognize pathogens?
Using specialized receptors: Pattern recognition receptors on host cell. Recognize patterns that are unique and initiate phagocytosis.
what are ex of pattern recognition receptors
Toll like receptors:
- TLR4: recognizes LPS (gram -)
- TLR2: recognizes peptidoglycan (gram +)
TL4 produces ____ which mediate inflammation and include IL1, IL6 and TNF-a and attract cells to site of infection leading to inflammation and cell ____
cytokins; death
what is an epitope
a fundamental unit of antigen that can induce an immune response.
the cells that particpate in adaptive immunity include:
- T lymphocytes
2. B lymphocytes
What is the structure of antibody molecule
- recognition site
2. antibody molecule
how can haptens be made immunogenic?
tagging it with carrier protein to trigger antibody production
Antibodies produced by B lymphocytes combat the antigen and neutralizes the effects of the antigen. All antigens are ___ which means they have the capacity to induce antibody formation. However, ____are low molecular weight proteins that can only bind to antibodies but can’t induce antibody production or elicit immune response.
immunogens; haptens;
Adaptive immunity/T cell response involves 3 steps:
- antigen recognition
- activation
- response
All T cells express ___antigens
CD (cluster of differentiation); specifically CD3 molecules or CD4
What are CD4 T cells
helper T cells; recognize antigens displayed on cell surface of dendritic cells in association with MHC class II and produce cytokines like interferon gamma that can activate macrophages and neutrophils to control intracellular infection. They also produce IL-2 (T cell growth factor) that helps expansion and proliferation of T cells. Can also make IL-4 and IL-5
What are CD8 molecules
cytotoxic T cells; recognize antigens displayed on the cell surface of DC’s in association with MHC class 1 molecules. They destroy virus infected cells. very specific!
Macrophages and dendritic cells participate in ___immunity as well as inducing ____ immune response. ____ can only participate in innate immune response bec they dont express ____ class molecules on their cell surface
innate; adaptive; MHC
IL-4B is cell ___ factor. IL-5-B is cell ____ factor
growth; differentiation
What are the classes of antibodies
IgM: pentamer IgG: travels through placenta IgE: participates in allergic reactions IgA: secreted in tears and colostrum IgD: B cell receptor
B cells respond to two types of antigens
- T cell independent (LPS) antigens
2. T cell dependent antigens (protein)
B cells also have an antigen receptor displayed on their cell surface and that is ____
IgD
Binding of LPS and other non protein antigens to IgD on B cell surface will directly activate B cells to produce ____
IgM. Only IgM will be produced during this recognition
IL-4 and IL-5 produce antibodies that belong to any class such as IgG, IgE, and IgA. This is called ____switching
class; in this context B cells can also present the antigens to CD4 T cells.
____ immunity is an immunity that is developed after exposure to an infectious agent or after vaccination
Active
Immune systems in newborns and and elerldy are considered to be weak. Newborns have immunity derived from maternal ___ and ___. Elderly lose tolerance to ___ antigens
IgA and IgG; self
