Bacterial scenario Flashcards
How does the immune system recognize bacterial infections?
Through Pattern Recognition Receptors (PRRs) like TLRs that detect bacterial components such as lipopolysaccharides (LPS), peptidoglycan, and flagellin.
What cytokines are released by innate immune cells during bacterial infections, and what are their effects?
TNF-α, IL-1β, and IL-6; they promote inflammation, recruit immune cells, and induce the acute phase response.
What do macrophages do in response to bacteria?
They phagocytose bacteria, produce inflammatory cytokines, and present bacterial antigens on MHC II to CD4+ T cells.
How do neutrophils respond to bacteria?
Neutrophils are recruited to the site of infection, where they phagocytose bacteria, release antimicrobial granules, and form neutrophil extracellular traps (NETs)
How does the complement system respond to bacterial infections?
It is activated via:
Classical pathway: Antibody-antigen complexes.
Alternative pathway: Direct bacterial surface recognition.
Lectin pathway: Recognition of mannose on bacterial surfaces.
What are the main effects of complement activation?
Opsonization (C3b coats bacteria for easier phagocytosis).
Formation of the membrane attack complex (MAC) to lyse bacteria.
Recruitment of immune cells (via C5a).
How are naive T cells activated during bacterial infections?
Dendritic cells present bacterial antigens on MHC II to CD4+ T cells.
Costimulation occurs via CD80/86 and CD28.
Cytokines (e.g., IL-12) direct differentiation.
What cytokines promote Th1 or Th17 responses, and why are they important in bacterial infections?
IL-12: Promotes Th1 cells, which enhance macrophage killing.
IL-6 and TGF-β: Promote Th17 cells, which recruit neutrophils and enhance mucosal immunity.
What are the main effector functions of Th1 cells during bacterial infections?
They secrete IFN-γ, which activates macrophages to kill intracellular bacteria and enhances antigen presentation.
How do Th17 cells contribute to bacterial defense?
Th17 cells secrete IL-17, which recruits neutrophils and stimulates antimicrobial production at mucosal surfaces.
How are B cells activated in response to bacterial antigens?
T-Dependent Activation: B cells internalize and present antigens to helper T cells, which provide cytokine help (e.g., IL-4, IL-21).
T-Independent Activation: Polysaccharide antigens directly cross-link B cell receptors.
What is the role of antibodies in bacterial defense?
IgM: Early response; promotes complement activation.
IgG: Opsonizes bacteria, neutralizes toxins, and activates complement.
IgA: Protects mucosal surfaces by neutralizing bacteria.
How does the immune system deal with intracellular bacteria?
Th1 cells secrete IFN-γ to activate macrophages.
CD8+ T cells kill infected cells presenting bacterial antigens on MHC I.
How does the immune system respond to extracellular bacteria?
Antibodies neutralize bacteria, promote phagocytosis, and activate the complement system.
Neutrophils and Th17 cells are critical for clearance.
Which cytokines drive inflammation during bacterial infections?
TNF-α, IL-1β, and IL-6.
Which cytokines promote macrophage activation?
IFN-γ from Th1 cells.
Which cytokines recruit neutrophils?
IL-17 from Th17 cells and chemokines like CXCL8 (IL-8).
What is the role of memory T cells in bacterial infections?
Memory Th1 and Th17 cells respond rapidly to reinfection by activating macrophages and recruiting neutrophils.
What is the role of memory B cells?
They quickly produce specific antibodies upon re-exposure to bacterial antigens.
How is inflammation resolved after a bacterial infection?
Regulatory T cells (Tregs) secrete IL-10 and TGF-β to suppress immune activity and prevent tissue damage.
What happens to neutrophils after the infection is cleared?
Neutrophils undergo apoptosis and are cleared by macrophages.
