Lecture 1: introduction Flashcards
- It’s present prior to exposure to antigen
- It’s early
- It has no memory
- It can’t distinguish among foreign antigens
Innate immunity AKA natural immunity
- It’s highly specific
- It’s inducible
- Immunity improves with each encounter
- Magnitude of the response increases because immune system remembers the antigen (has “memory”)
Acuired immunity AKA specific immunity AKA adaptive immune response
Innate:
Resistance:
- Unchanged on repeated infection
- No memory
- Fast
Acquired
Resistance:
- Improved by repeated infection
- Memory
- Slow
Resistance: Innate immunity vs. acquired immunity
Innate:
Specificity:
Structures shared by similar groups of microbes, called pathogen associated molecular patterns (PAMPS) ex. Mannose and N-formyl-Met
Acquired:
Specificity:
Very precise interactions
Specificity: Innate immunity vs. acquired immunity
Innate:
Cells:
- Phagocytes
- NK Cells (lymphocytes)
Acquired:
Cells:
- T cells (lymphoctes)
- B cells (lymphocytes)
Cells: Innate immunity vs. acquired immunity
Innate:
Diversity: Limited diversity (germ-line encoded)
Specific:
Diversity: Very large, receptors are produced by recombination
Diversity: innate vs. specific
Innate:
Molecules: Lysozyme, complement, acute phase proteins, IL-1, IFN-alpha and beta; Toll Like Receptor
Specific:
Molecules:
Antibodies and cytokines
Molecules: Innate immunity vs. specific immunity
Defense, resist pathogens, foreign bodies, and abnormal cells
Primary function of the immune system
Immune system can respond up to 10^9 antigens
Each lymphocyte arises from a single precursor cell which responds to only one antigen
pathogen can activate several cells recognizing it
Clonal selection theory
- A single progenitor cell gives rise to a large number of lymphocytes, each with a different specificity
- Removal of potentially self-reactive lymphocytes by clonal deletion
- Pool of mature naive lymphocytes
- Proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells.
Steps of clonal selection
The immune system remembers a pathogen it has seen before
Memory
It takes about 5-10 days to manifest
A. Primary immune response
B. Secondary immune response
Primary immune response
- It takes 2-5 days.
- It occurs after subsequent exposure to the same antigen.
- It is more effective and has longer duration
A. Primary immune response
B. Secondary immune response
B. Secondary immune response
Immune responses are specific for each antigen or parts of antigens called epitopes or antigenic determinants via specific receptors on lymphocytes (B and T cells). These lymphocytes rapidly replicate into an army of cells capable of attacking the pathogen. These cells are the ONLY cells with specific receptors for antigen.
B cell antigen receptor: monomeric IgM
Th cell antigen receptor: TCR and CD4. CD4 assists TCR
Cytotoxic T cell antigen receptor: TCR and CD8. CD8 assists TCR
Specificity: Specific immune system
The immune system can respond to many antigens. T and B cells express and antigen receptor with a slightly different shape for each entigen.
Clonal selection theory allows immune system diversity
Diversity: specific immune response
It’s the increase in the number of cells that express identical receptors for the antigen. Those cells are derived from the clones that recognized antigen.
Clonal expansion
All responses wane with time returning to the basal state
If there are too many lymphocytes, you get generalized inflammation
When antigen is eliminated, cells that recognize it, die by apoptosis
Homeostasis: return to homoestasis after clonal expansion
The normal immune system responds to foreing antigens while remaining unresponsive to host components. Immune system does this through recognition of MHC antigens specialized for self proteins. There are 2 classes of MHC: MHCI and MHCII. The immune system is trained to recognize but not respond to their own MHC, in most cases the immune system only responds to for. antigens when it’s bound to self MHC
Discrimination of self vs. non-self
- It has an alpha chain and a beta-globulin unit, so it has one chain and a peg leg.
- It is present on all nucleated cells
- It presents to CD8 (cytotoxic) T cells and NK cells
MHC I
- It has 2 chains an alpha chain and a beta chain
- It has 2 legs
- It presents to Th cells
- It is expressed by antigen presenting cells (dendritic cells (best), macrophages (need to be induced by IFN-gamma), and B cells (in secondary immune response)
MHC II
- It’s achieved by immunization, i.e. exposure to foreign antigen stimulating a set of specific responses
- It’s inducible
- It can be intentional exposure (vaccination)
- It can be unintentional exposure (infectrion)
Acquired immunity
- It’s mediated by antibodies produced by plasma cells (B cells)
- It can be transferred by serum
- Antibodies bind to foreign antigen and target that antigen for lysis via complement, or removal by phagocytes
Humoral immunity
- It’s mediated by T cells
- T cells produce cytokines which activate other cells such as macrophages or T cells to effectively deal with antigen
Cellular immunity
- It’s a passive transfer of antibodies or cells
- There is no active effort in the part of the immune response
- It works fast
- There is no memory
- There is no memory because the body didn’t mount the response, the antibodies were introduced to the body.
- Ex. Human tetanus immunoglobulin
- Ex. Anti-venom
Passive immunity
What is the B cell receptor (BCR)?
A. monomeric IgM
B. Pentameric IgM
C. IgG
D. IgE
A. Monomeric IgM
Monomeric IgM binds to antigen. B cells also express IgD but we don’t know IgD’s function.
- Cognitive phase
- Activation phase
- Effector phase
- Termination phase
The phases of the immune response
- It involves antigen binding by B cells and T cells
- B cells can bind free antigen
- T cells can’t bind free antigen, the antigen must be presented to the T cell as a linear determiannt on MHCII of an APC preferrably a dendritic cell
Cognitive recognition phase
- Cels proliferate in response to cytokine signals
- Immune response is amplified
Activation phase
Antigen is eliminated
Effector phase
Immune system is downregulated after the antigen has been removed. If immune system is not downregulated you get autoimmunity.
Termination phase
- After antigen recognition, there is lag phase of 5-10 days-activation phase
- first antibody to be produced is pentameric IgM
- IgG is produced next
- These are low affinity antibodies
- the same B cells produce IgM and IgG. This is called class switching
- levels of antibody peak betw. days 20-30
- antibody levels decrease, antigen is cleared
Primary immune response
- immune response is quicker due to presence of memory cells
- antibodies peak 2-5 days, activation phase is short
- higher magnitude response
- longer duration
- IgG is predominant antibody, but IgM is present as well
- IgM is always part of the immune response
Secondary (Anamnestic response)
- It has primary and secondary phases
- Secondary responses are faster
- It’s mediated by memory T cells
- Higher levels of activation
Cellular immune response
B cells and T cells recognize and respond to for. antigens via specific receptors (BCR= monomeric IgM, TCR=TCR w/ CD3 extension so it can undergo signal transduction)
NK cells do not have specific receptors
Lymphocytes
macrophages/monocytes ingest and destroy infectious agents and present antigen to T cells
Macrophages and dendritic cells are monocytes
mononuclear phagocytes
They have many cytoplasmic granules, contain anti-microbial compounds, and some able to phagocytize.
neutrophils, basophils, and eosinophils are__
granulocytes
