LT 12 The Respiratory System PT3 – The Immune response Flashcards
Q: What are the primary roles of neutrophils in the immune response?
A: Neutrophils are the most abundant leukocytes in the blood, first responders to infection, and dominate in acute infection. They phagocytose microbes, release antimicrobial enzymes, and undergo Netosis. Neutrophils are produced in the bone marrow and rapidly recruited to injured tissues within minutes.
Q: How do monocytes contribute to immune defense?
A: Monocytes phagocytose microbes in the blood. Upon leaving the blood and entering tissues, they differentiate into macrophages. Monocytes originate from the common myeloid progenitor in the bone marrow and can be long-lived.
Q: Describe the function of macrophages in the immune system.
A: Macrophages are present in tissues and are derived from monocytes or yolk sac progenitors (for tissue-resident macrophages). Their main roles include phagocytosis, cytokine production, and antigen presentation.
Q: What is the role of dendritic cells (DCs) in the immune response?
A: Dendritic cells are strategically located in peripheral tissues to sense and capture pathogens and antigens. They are crucial antigen-presenting cells (APCs) that initiate innate and adaptive immune responses, bridging the two systems.
Q: What is the immune environment of the normal lung/respiratory tract?
A: The normal lung/respiratory tract maintains homeostasis with alveolar macrophages as resident tissue cells. They are the first responders to infection, recognizing viral infections through pattern recognition receptors (PRRs) and driving interferon production and cytokine release.
Q: Outline the steps in the maturation process of dendritic cells.
A: Immature DCs are highly phagocytic in peripheral tissues. Upon capturing a pathogen or being infected by a virus, PRR activation triggers DC maturation, leading to a decrease in phagocytosis, increased expression of MHC-I and MHC-II molecules, and co-stimulatory molecules. Mature DCs then migrate to lymph nodes.
Q: What are the key steps in the MHC-I antigen processing pathway?
A: The MHC-I pathway occurs in all nucleated cells and involves processing cytosolic proteins (self, viral, or phagosomal leakage). Peptides are broken down by the proteasome, transported into the ER via TAP, and loaded onto MHC-I molecules for presentation on the cell surface to CD8 T cells.
Q: What are the key steps in the MHC-II antigen processing pathway?
A: The MHC-II pathway processes extracellular proteins. These proteins are phagocytosed, broken down in lysosomes, and loaded onto MHC-II molecules in endosomal compartments. The loaded MHC-II molecules are then presented on the cell surface to CD4 T cells.
Q: Compare and contrast MHC-I and MHC-II molecules and their functions.
A: MHC-I molecules present endogenous peptides to CD8 T cells, leading to the destruction of infected cells. MHC-II molecules present exogenous peptides to CD4 T cells, which provide help to other immune cells like macrophages and B cells. MHC-I is expressed on all nucleated cells, while MHC-II is expressed primarily on APCs.
Q: What is MHC restriction?
A: MHC restriction refers to the requirement that T cells recognize antigens only when presented by an individual’s own MHC molecules. CD8 T cells are restricted to MHC-I, while CD4 T cells are restricted to MHC-II.
Q: Explain how naïve T cells are activated and the importance of co-stimulation.
A: Naïve T cells are activated in secondary lymphoid tissues by APCs that present antigen-MHC complexes. Activation requires two signals: specific antigen recognition by the T cell receptor (TCR) and co-stimulatory signals provided by APCs. Co-stimulation is crucial to ensure T cells are appropriately activated to perform their effector functions.
Q: What is MHC restriction?
A: MHC restriction refers to the requirement that T cells can only recognize antigens when they are presented by the host’s own MHC molecules. CD8 T cells are restricted by MHC-I molecules, and CD4 T cells are restricted by MHC-II molecules.
Q: Which type of T cells are restricted by MHC-I molecules?
A: CD8 T cells are restricted by MHC-I molecules.
Q: Which type of T cells are restricted by MHC-II molecules?
A: CD4 T cells are restricted by MHC-II molecules.
Q: What does the T cell receptor (TCR) interact with during antigen recognition?
A: The T cell receptor interacts with both the peptide and the MHC molecule, recognizing them as a single complex.
