Lecture Notes on the Immune System Functioning

Summary

In this lecture, Danielle explained how our immune system functions, focusing on its ability to differentiate between self and non-self entities. She described the immune system's components and their roles in combating foreign substances like bacteria, viruses, parasites, fungi, cancer cells, and donor organs, which are collectively referred to as antigens.

Key Points

The Importance of Recognizing Foreign Substances

• The immune system attacks anything recognized as foreign.
• For the purpose of this explanation, the focus is on bacteria, but the concept applies to multiple foreign substances identified as antigens.

How the Immune System Responds to Bacteria

• Outcomes: Either the body is overwhelmed by the bacteria or the immune system defeats it.
• Response Mechanism: The immune system's white blood cells (leukocytes) tackle bacteria by isolating, inactivating, and removing them.

Main Components of the Immune System

• Aspecific (Innate) Immunity:
  • Responds to all foreign bodies generically.
  • Includes physical barriers like skin, saliva, and stomach acid.
  • Phagocytic cells like macrophages and neutrophils.
  • Chemicals like cytokines (including interleukins and interferons) and the complement system.
• Specific (Adaptive) Immunity:
  • Targets specific antigens with specialized cells.
  • Divided into cell-mediated immunity (handled by T-cells) and humoral immunity (handled by B-cells).

Response to Inflammation (Using a Skin Wound as an Example)

• Initial Reaction:
  • Increased blood flow due to vasodilation influenced by histamine and bradykinine.
  • Classical signs of inflammation: redness (rubor), heat (calor), pain (dolor), swelling (tumor), and loss of function (functio laesia).
• Permeability: Vessels become more permeable allowing essential substances to reach the inflammation site.
• Activation of the Complement System:
  • Complement proteins attract leukocytes to the inflammation site and aid in phagocytosis.
• Role of Leukocytes:
  • Neutrophils arrive first for phagocytosis.
  • Neutrophils secrete IL-1, which causes fever, aiding in fighting off the infection.
  • Macrophages assist neutrophils and deal with the cleanup.
• Specific Immune Response:
  • Macrophages present fragments of the bacteria to T-cells, activating a specific T-cell.
  • This leads to the proliferation of T-cells, including Cytotoxic T-cells, Helper T-cells, Memory T-cells, and Suppressor T-cells.
  • Helper T-cells activate B-cells, which are in lymph nodes.
  • B-cells proliferate into memory cells and plasma cells that produce antibodies.

Antibodies and Their Function

• Types of Antibodies: IgA, IgD, IgE, IgG, and IgM.
• In the given scenario, IgG antibodies are produced.
• Antibodies attach to bacteria enabling quicker elimination by T-killer cells and macrophages, neutralize bacterial toxins, and activate the complement system.

Conclusion

The immune system effectively counters foreign invaders through a complex interplay of its innate and adaptive components. The next lecture will explore hypersensitivities in the immune system, focusing on allergies and autoimmune diseases.

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