Immunity to infectious Disease and Vaccines Flashcards
Why is immunity to infectious disease important?
1/3 of world (and US) deaths from ID, immune response necessary for survival, increased number or antibiotic resistant B, increase crowding and travel allows exposure to evolving viruses
What parts of the immune system are activated from virus infection in order?
very early/immediate: innate immune response IFN and cytokines, next NK cells mobilize to infection site, there is recognition of viral antigens, day 4-6 adaptive immune response (CD8 cells), followed by Ab production, develop memory, then can get anti-host pathologic effects (too vigorous response)
How des the body first recognize a viral infection?
RIG-1 receptor in infected cell, recognize viral dsRNA, or toll like receptors (TLR 3,7,8,9) recognize dsRNA, vsRNA, CpG DNA
Once viral infection is recognized, how is the innate immune system activated?
IFN regulatory factor and NfkB activated in dendritic cell, which stimulates secretion of INF alpha and beta and inflammatory cytokines (TNFa, IL6, IL12)
How does IFN alpha and Beta induce a cell into an anti-viral state?
translation of protein kinase R-> block eukaryotic initiation factor 2a activating BCL2 and caspase->apoptosis, 2,5-oligoadenylate cyclase Synthetase-> activate Rnase L-> degrades vRNA, and Mx protein-> blocks viral transcription
What cells in the immune system does IFN alpha and Beta activate?
dendritic cells, macrophages, NK cells T and B cells
Once activated by IFN alpha and Beta, what do dendritic cells and macrophages do during viral infection?
“garbage collectors”, phagocytosis, Ag presentation, release of cytokines, kill virus infected cells
Once activated by IFN alpha and IL-12, what do NK cells do during viral infection?
cytotoxic to virus infected cells, produce IFN-gamma to activate adaptive immune system, shut down virus replication in cells, buys time for adaptive immune response
How does the adaptive immune system recognize virus or viral infected cells?
Viral Ag on EC surface(membrane or capsid AG on infected cells, viral structural proteins inserted in host membrane); Ab also recognize viral surface Ag on virion
What are the primary and secondary responses of adaptive immune system? what role does each play?
1- T cell, leads to resolution of infection; 2- Ab response, contributes to recovery from infection
In the primary T cell response what activates CD4+ cells and what do they do? Be specific for different kinds.
Both activated by IL-12 and IFN-gamma, TH1- produce IL2 to activate macrophage, induce T (CD8) and NK cell activation and proliferation, promote B cell production if Ig; TH2- provide help for B cell activation, differentiation, production of Ab, also activate eosinophils
In the primary T cell response what activates CD8+ cells and what do they do?
activated by IL-2 (from CD4+) cytotoxic to infected host cells, produce IFN-gamma and TNF which inhibit viral replication; principle surveillance (peptide and MHC class I)- direct killing by perforin and granzymes or activation of FAS ligand-> apoptosis
What is the course of Ab production in viral infection?
CD4+ help viral antigen specific B cells in lymph node- proliferate, clonal expansion, differentiation, somatic hypermutation occurs and selection for highest affinity B cells producing Ab to become plasma cell and migrate to bone marrow
Once made what does Ab against viral Ag do with extracellular virions?
binds extracellular virus and either prevents entry to host cell and/or enhance phagocytosis and mediates opsonization of viral particles (IgM, IgG and IgA)
Describe the features of antibody dependent cell cytotoxicity (ADCC).
Ab binds viral antigen on EC surface, activation of complement= lysis of infected cell
What role does immunologic memory play in viral infections?
preformed Ab, memory T cells and B cells can rapidly expand and differentiate into effector cells (much quicker and stronger response), reason behind viral vaccines (mom can pass to baby- Ab)
What are some examples of anti-host effects of virus in impairing the immune system?
immune evasion, avoidance of recognition, inhibit humoral immunity, inflammatory response, immunosuppression of host, infection of host immune cells (shut down or down regulate IFN and cytokine production)
How can viruses evade the immune system?
antigenic drift and shift (HIV and Flu), molecular mimicry (steal some of host genome so recognized as self)
How can viruses avoid recognition by immune system?
latent infection, replicate in “privileged” sites in host like CNS (very little to no immune activity), impair recognition by reducing MHC expression on infected cells
What are the pathologic consequences of the immune response induced by viral infection?
excessive cytokine production (cytokine storm), antiviral Ab form immune complexes causing disease, or virus specific T cells cause host damage
What are the consequences and some viral examples of excessive cytokine production?
acute respiratory distress (ARDS) seen with Flu A H5N1, H1N1 and Sars, usually mid-range of age, immune competent; in Ebola-> cytokine and damage to endothelial cells (infected)-> loss of vascular integrity, hemorrhage and vasomotor collapse may occur
When immune complexes are formed what condition can ensue with immune complex disease?
glomerulonephritis
When virus specific T cells cause host cell damage, what else can happen? Viral examples?
induce autoimmunity; Hep B, Coxsacki B virus (islet B cells), and enterovirus-> anticardiomyocyte CD8 cells
What is the general immune response to bacterial and fungi?
induce inflammatory responses, produce cytotoxic endotoxins (LPS) or exotoxins (diphtheria toxin), recognition of B by PAMPs and recognized host TLR
What are the features of the innate immune response?
chemotaxis: C3a and C5a recruit phagocytic cells, following complement activation via alternate path, phagocytes (Macrophage and Neutrophils) engulf and destroy bacteria
What are the adaptive effector response to bacterial infection?
CD4+ T cells produce- IFN gamma and TNF to activate macrophage and induce inflammation, IL-4,5,6 induce Ab formation
What specific CD4+ T cell is important in resisting bacterial infection? Cytokines produced?
TH17 producing IL-17 (recruits neutrophils) and IL-22
What role do CD8+ T cells in bacterial infection response?
intracellular organism killed by killing the infected cell (very important in reponse to TB), secretes IFN-gamma to activate macrophages (kill infected B cells)
What are the Ab dependent anti-bacterial defenses?
neutralize toxins- Ab to toxin binds to toxin blocking binding of microbes to cellular receptors, increased opsonization and phagocytosis, activate and efficient targeting of complement
What are the bacterial defenses against host response to infection?
encapsulation, evade complement activation, kill phagocytes before ingestion, resistance to phagocytosis, phagosome-lysome fusion and lysosomal killing, intracellular microbes, can survive in phagocytes
What are the immunopathological reactions induced by bacteria?
excessive cytokine release (endotoxin septicemic shock, TSS) due to LPS from gram (-) bacteria; and superantigen of massive cytokine release (TSS) of staphylococcal toxin