Immune response to infection Flashcards
What occurs in the innate response?
Fast-acting response using cells with germline coded receptors. It includes 3 main parts:
- Physical barriers e.g. Skin, mucous, epithelial cells
- Humoral e.g. Complement, lectins, pentraxins, antimicrobial peptides
- Cellular e.g. Neutrophils, macrophages, dendritic cells, NK cells
What occurs in the adaptive response?
Slower-acting but long-lasting. Uses cells with variable receptors that mature over time through DNA recombination. In includes 2 main parts:
- Humoral e.g. Antibodies and complement
- Cellular e.g. CD8 cytotoxic T cells, T helper cells, T regulatory cells
What are the differences between innate and adaptive response?
- Specificity - innate is specific to structures shared by classes of microbes called pathogen associated molecular patterns. Adaptive is specific to antigens.
- Receptors - receptors in the innate response are encoded in germline with limited diversity whereas adaptive are encoded by genes produced by somatic recombination of gene segments leading to greater genetic diversity.
- Distribution of receptors - In innate the receptors are non-clonal i.e. there are identical receptors on all cells of the same lineage. In adaptive the receptors are clonal so clones of lymphocytes with distinct specificities express different receptors
What are the 4 types of pathogen niches during infection?
- Extracellular e.g. staphylococcus, streptococcus
- Intracellular e.g. salmonella, chylamydia
- Surface adherent e.g. enteropathogenic and enterohaemorrhagic E.coli
- Intracellular but cytosolic e.g. viruses
What occurs immediately after tissue damage or pathogen identification?
First responders are always neutrophils followed by macrophages that become activated upon interaction with microbes. Phagocytes control infection and limit tissue damage. Gene expression changes are important in the activation of phagocytes caused by interleukins.
What 3 things can uncontrolled phagocytosis cause?
- Granulomas
- Excessive inflammation and inappropriate adaptive immunity
- Tissue damage
What is the function of interferons?
Interferons are special cytokines that have direct antiviral activities by causing the expression of antiviral genes including:
- Nucleases
- Inhibitors of virus entry and exit
- Inhibitors of viral uncoating and replication
- Inhibitors of protein translation
They also enhance T-cell responses, have anti-inflammatory actions and are involved in tissue repair.
What are the 4 soluble effector and 2 cellular effector mechanisms involved in humoral innate immunity?
Soluble effectors:
- Complement mediated bacterial destruction
- Lectin binding to neutralise cell attachment or entry
- Iron chelation via siderophores to prevent replication
- Antibiotic-like peptides
Cellular effectors:
- Reactive oxygen and nitrogen radicals
- Acidification and digestion within phagosomes.
How do antigen presenting cells such as dendritic cells activate T cells?
Activated macrophages and dendritic cells present antigens in combination with MHC-I or MHC-II to T cells.
Cytokines produced by antigen-presenting cells produce a suitable environment for T-cell activation
E.g. IL-12 promotes T-cell replication
T cells provide cytokines that activate phagocytes
E.g. IFN gamma upregulates MHC-II expression for antigen presentation
What are the cytokines and principal target cells of th1, th2 and th17 t cells.
th1 - produces inferferon gamma, targets macrophages
th2 - produces il4,5,13 which target eosinophils
th17 - produces il17,22 which target neutrophils
What is the general timing of the cellular immune response?
Innate occurs between 0 to 12 hours after infection
Adaptive from 12 hours to 5 days.
What is the impact of age on the immune response?
As age increases, thymic output decreases so the number of naive T cells decreases over time but the number of memory T cells increases over time.
