Immunopathology of allergy - Appendix: Key components in allergic reaction (Background reading)

13 important questions on Immunopathology of allergy - Appendix: Key components in allergic reaction (Background reading)

What do mast cells release when they degranulate?

  • Stored: histamine, heparin and proteases
  • Synthesized by the activated cells: leukotrienes, prostaglandins, cytokines, chemokines and peptide growth factors

What do basophils secrete?

Large quantities of Th2 cytokines (IL-4 and IL-13) and newly synthesised leukotriene C4.

What do basophils and mast cells have in common?

  • Presence of basophilic granules in the cytoplasm
  • Surface expression of IgE receptor (FCeRI)
  • Release of chemical mediators in response to various stimuli
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By what is eosinophilia in allergic diseases mediated?

By IL-5 producing T cells.

What can eosinophils cause and how?

Organ dysfunction by
  • cytotoxicity
  • fibrosis

What do eosinophils produce and store?

Biologically active molecules, including cytotoxic proteins, lipid mediators, chemotactic peptides and cytokines.

What do the dendritic cells do in the lymph nodes?

  • They induce CD4 T helper cell differentiation
  • CD8 T cell activation
  • Transfer some of their encountered antigens to B cells

Why do lung and skin DCs play a crucial role during the chronic phase of the allergic inflammation?

They produce chemokines that attract other inflammatory cells to inflamed tissue.

How is IgE-switch and differentiation of B cells triggered?

CD4+ Th2 cells that produce IL-4 and express CD40L

What are sensing cytokines?

They are released from the epithelial cells of the mucous membranes and signals to the allergen-presenting DC to take up incoming allergens and bring them to the lymph nodes.

What are T-cell instructing cytokines?

They will instruct undifferentiated T helper (CD4+) cell to develop into different kinds of cells, each of them equipped for different kinds of immune response:
  • IL-12 and IFN-y --> Th1 cells
  • IL-4 --> Th2 cells

What are the effector cytokines?

The cytokines by which Th cells exerts their action.
  • Th2 --> IL-4, IL-13 which instructs B-cells to produce the allergy antibody IgE
  • IL-5 --> stimulates the bone marrow to form the eosinophilic granulocyte
  • IL-9 + IL-13 --> create the allergic inflammation, e.g. Asthma in the lung

What do the resolving cytokines do?

IL-10 and TGF-beta down-regulate the allergic inflammation, restoring the homeostasis of the immune system.

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