immune defence against bacteria

What is the primary mechanical barrier against microbes?

Skin, which retards the entry of microbes.

What is the pH range of the acidic environment that helps defend against pathogens?

pH 3-5.

How do mucous membranes contribute to immune defense?

They trap foreign microbes with mucus and propel them out using cilia.

What role does body temperature play in immune defense?

Body temperature and fever response inhibit the growth of some pathogens.

How does stomach acid contribute to defense against pathogens?

Low pH of stomach acid kills undigested microbes.

What is the function of lysozyme in the immune system?

Lysozyme cleaves bacterial cell walls.

What is the role of interferon in the immune response?

Interferon induces antiviral defenses in uninfected cells.

What is the function of complement in the immune system?

Complement lyses microbes or facilitates phagocytosis.

What is the role of phagocytic cells in immune defense?

They internalize and break down foreign macromolecules and kill whole organisms.

What triggers the inflammatory response?

Tissue damage and infection induce leakage of vascular fluid containing antibacterial serum proteins.

What is the role of dendritic cells in activating the adaptive immune system?

Dendritic cells pick up antigens, migrate to lymph nodes, and activate T helper and cytotoxic T cells.

What cytokines influence the polarization of T helper cells?

IL-12 influences TH1, IL-4 influences TH2, and IL-23 influences TH17.

What is the primary function of TH1 cells?

TH1 cells produce IFN-gamma, IL-2, and TNF-alpha, appropriate for intracellular infections.

What do TH2 cells primarily respond to?

TH2 cells respond to parasitic infections and produce IL-4, IL-5, and IL-13.

What is the function of cytotoxic T cells?

They recognize infected cells via MHC I and produce perforin to kill them.

What is the role of B cells in the immune response?

B cells proliferate, undergo clonal expansion, and produce antibodies.

What type of antibody is primarily produced in the primary immune response?

IgM, which induces complement fixation and viral neutralization.

What are the main types of infectious agents?

Viruses, bacteria, fungi, protozoa, and helminths.

What is the innate immune response to extracellular pathogens?

It involves antibodies, complement, phagocytosis, and neutralization.

How do macrophages recognize bacteria?

Macrophages recognize opsonized bacteria and various bacterial products through surface receptors.

What are common inflammatory cytokines involved in the immune response?

IL-1, IL-8, IL-12, and TNF-alpha.

What is the role of NK cells in the immune response?

NK cells detect and kill bacterially infected cells.

What is the significance of Th17 cells?

Th17 cells produce IL-17, which is important for neutrophilic responses to extracellular bacteria and fungi.

What immune evasion strategies do bacteria employ?

They can inhibit chemotaxis, destroy phagocytes, and prevent lysis after phagocytosis.

What is the most prevalent fungal infection in humans?

Dermatophytoses.

What is the most common species of Candida that causes infection?

Candida albicans.

How does innate immunity respond to fungal infections?

Barriers, commensal organisms, complement activation, and phagocytosis are key components.

What is the role of Th17 responses in fungal infections?

Th17 responses secrete IL-17 and IL-22, which produce anti-microbial peptides.

What is adaptive immunity to bacteria?

Bind and neutralise toxins

Toxins opsonised for phagocytosis

Opsonise bacteria

By direct mechanisms (Fc interacting with phagocyte FcR)

Inducing complement cascade (classical)

Direct bacterial lysis

Labelling for phagocyte recognition + phagocytosis

Release of C5a + 3a

Intercellular bacteria - CMI (T cells)

What is the mechanical barrier that retards the entry of microbes?

Skin

What is the pH range of the acidic environment that helps defend against microbes?

pH 3-5

What role does the mucous membrane play in defending against pathogens?

It provides normal flora for attachment, traps foreign microbes, and has cilia that propel microbes out.

How does body temperature or fever response contribute to immune defense?

It inhibits the growth of some pathogens.

What is the function of stomach acid in microbial defense?

It kills undigested microbes due to its low pH.

What is the role of lysozyme in the immune response?

It cleaves bacterial cell walls.

How does interferon contribute to antiviral defenses?

It induces antiviral defenses in uninfected cells.

What is the function of complement in the immune system?

It lyses microbes or facilitates phagocytosis.

What is the role of phagocytic cells in the immune response?

They internalize and break down foreign macromolecules and kill whole organisms.

What triggers the inflammatory response in the immune system?

Tissue damage and infection induce leakage of vascular fluid containing antibacterial serum proteins and influx of phagocytic cells.

What is the role of dendritic cells in activating the adaptive immune system?

They pick up antigens, migrate to lymph nodes, and activate T helper and cytotoxic T cells via MHC presentation.

What cytokines influence the polarization of T helper cells?

IL-12, IL-4, and IL-23.

What are the three subsets of T helper cells and their associated functions?

TH1: intracellular infections; TH2: parasitic infections; TH17: extracellular bacteria and fungi.

How do cytotoxic T cells recognize infected cells?

They recognize specific antigens presented by MHC I.

What is the primary antibody produced during the primary immune response?

IgM.

What are the two types of pathogens that can cause infectious diseases?

Intracellular pathogens (viruses, certain bacteria) and extracellular pathogens (viruses, bacteria, protozoa, worms, fungi).

What are the protective immunity mechanisms against intracellular pathogens?

Tc cells, Antibody Dependent Cellular Cytotoxicity, and NK cells.

What is the role of macrophages in the immune response to bacteria?

They recognize opsonized bacteria and a variety of bacterial products, initiating phagocytosis.

What are some bacterial immune evasion strategies?

Inhibiting chemotaxis, destroying phagocytes, and preventing lysis after phagocytosis.

What is the most prevalent fungal infection in humans?

Dermatophytoses.

What is the most common species of Candida that causes infection?

Candida albicans.

What immune response is primarily involved in combating fungal infections?

Innate immunity, particularly through phagocytosis and cytokine production.

What is the role of Th17 responses in fungal infections?

They secrete IL-17 and IL-22, which produce anti-microbial peptides.

What are the common species of Aspergillus that can cause infections?

A. fumigatus, A. flavus, and A. niger.

What is the role of surfactant proteins in the immune response to fungi?

They enhance chemotaxis, binding, phagocytosis, and oxidative killing.

What role do macrophages play in recognizing bacteria?

Macrophages have a large number of surface receptors that recognize opsonised bacteria.

What is complement opsonisation?

It enhances phagocytosis by marking bacteria for destruction.

What is the function of the membrane attack complex in the innate immune response?

It directly lyses bacteria by forming pores in their membranes.

How do C5a and C3a contribute to the immune response?

They have chemotactic action, attracting immune cells to the site of infection.

What is the role of macrophages and neutrophils in phagocytosis?

They mediate the process of engulfing and destroying pathogens.

What types of receptors do macrophages use to recognize bacterial products?

Macrophages use mannose receptors, scavenger receptors, CD14, and C11b/CD18.

How do some extracellular bacteria evade recognition by macrophages?

They have a thick polysaccharide capsule that is not recognized by macrophage receptors.

How do intracellular bacteria evade the innate immune response?

They grow within phagosomes, avoiding detection by immune cells.

What activates Cytotoxic T cells?

Cytotoxic T cells are activated by MHC I.

What do Cytotoxic T cells produce upon recognizing infected cells?

They produce perforin and engage in Fas-Fas ligand interaction.

How are Cytotoxic T cells stimulated to proliferate?

They can be stimulated by IL-2 from helper T cells.

What types of infections are Cytotoxic T cells appropriate for?

They are appropriate for intracellular infections such as viruses, bacteria, fungi, parasites, and cancer.

What is the primary antibody produced by B cells during the primary response?

IgM, which induces efficient complement fixation and viral neutralization.

What process do B cells undergo after activation?

B cells proliferate, undergo clonal expansion, and selection.

What determines the type of antibody produced by B cells?

The type of antibody is determined by signals the B cell encounters during class switching, influenced by T helper cells.

What is the role of antibodies produced by B cells?

Antibodies can bind to pathogens, inducing ADCC, complement fixation, and neutralization.

Name two types of pathogens that cause infectious diseases.

Viruses and bacteria.

What are examples of intracellular pathogens?

Viruses, certain bacteria, and protozoa.

What type of immunity is provided against intracellular pathogens?

Protective immunity is provided by Tc cells, Antibody Dependent Cellular Cytotoxicity, and NK cells.

What type of pathogens are considered extracellular?

Extracellular pathogens include viruses, bacteria, protozoa, worms, and fungi.

What is the protective immunity mechanism against extracellular pathogens?

It involves antibodies, complement, phagocytosis, and neutralization.

What types of pathogens are found on epithelial surfaces?

Bacteria, fungi, and worms.

What is the role of inflammatory cells in the immune response?

Inflammatory cells contribute to protective immunity against extracellular pathogens.

What is the role of dendritic cells in the activation of the adaptive immune system?

Dendritic cells act as professional antigen-presenting cells (APCs) that pick up antigens, migrate to lymph nodes, and activate T helper cells via MHC II and cytotoxic T cells via MHC I.

What factors dictate the cytokines and co-stimulatory molecules presented by mature dendritic cells to naïve T cells?

Cytokine recognition and/or pattern recognition receptor (PPR) ligation at activation.

What happens to T helper cells after they are activated by MHC II?

They proliferate rapidly in the lymph node and mature into effector T helper cells after about a week.

What is the function of effector T helper cells after maturation?

They leave the lymph node to provide help for B cells or cytotoxic T cells and respond to cytokines at the site of infection.

How can the subset of T helper cells change during an immune response?

The subset can be changed or reinforced based on the type of stimulation and the cytokines present.

What cytokines influence the differentiation of TH1 cells?

TH1 cells are influenced by IL-12 and IFN-gamma, producing IFN-gamma, IL-2, and TNF-alpha, which are appropriate for intracellular bacterial or viral infections.

What is the role of TH2 cells in the immune response?

TH2 cells are influenced by IL-4 and produce IL-4, IL-5, and IL-13, which are important for combating parasitic infections.

What cytokines influence the differentiation of TH17 cells?

TH17 cells are influenced by IL-23, IL-6, IL-1, and TGF-beta, producing IL-17A, IL-17F, IL-21, and IL-22, which are important for responses to extracellular bacteria and fungi.

What is the function of primary lymphoid organs?

regulate the development of immune cells from immature precursors, contain either T or B cells

What is the function of secondary lymphoid organs?

Sites where mature lymphocytes first encounter antigens and are activated, increase size with age

What is the initial action taken by mast cells in response to bacteria entering tissue?

Mast cells detect the problem and release alarm signals like histamine.

Which types of blood cells are recruited to the site of infection?

Monocytes, neutrophils, and lymphocytes.

What do monocytes, neutrophils, and lymphocytes do once recruited?

They stick to blood vessel walls and squeeze through into the infected tissue.

What do activated macrophages release to further the immune response?

Cytokines (chemical messengers like IL-1, TNF-α) and signals that attract more immune cells.

What happens to blood vessels during the immune response?

Blood vessels become leaky, which can cause tissue damage.