Immune System Overview

Immune System Overview


The immune system is the primary defense mechanism that comprises an extensive network of cells, organs, and tissues. The primary function is to recognize and neutralize microorganisms (bacteria, viruses, fungi, and parasites) and "cells" that may cause harm to the organism (i.e., cancer cells).

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Components of the immune system

  • WBC (white blood cells): The primary defenders are white blood cells produced in the bone marrow. They circulate through the body in search of harmful microorganisms or abnormal cells. Once encountered, an immune response is initiated. Various types of white blood cells exist (lymphocytes, natural killer cells, and other types of immune cells).
  • Antibodies: With the help of special proteins (antibodies), the immune system is able to identify specific other proteins (antigens) on cells or microorganisms thus marking them as foreign. Once identified, the antibodies signal a cascade of events for the destruction of these antigens.
  • Organs crucial to the immune system include the lymphatic system (an organ made of vessels and nodes which deals with cancer cells, and microbes by providing a means of transport of WBC); the spleen (an organ that filters the blood by eliminating microbes and breaking down old or damaged red blood cells); bone marrow (special organ found in bones, it produces the WBC); and thymus (The thymus gland assists in instructing and preparing T cells to identify and fight particular pathogens and foreign elements while distinguishing them from healthy tissues. This process is crucial in ensuring that the immune system can selectively target and eliminate harmful invaders in an efficient and effective manner).

Breakdown of the immune system

  • Innate immunity: also known as natural or non-specific immunity, is a form of defense against harmful foreign substances that enter the body. It provides an immediate protective action by targeting a wide range of potential invaders without requiring prior exposure or specific recognition of a particular antigen. This first line of defense plays a critical role in the early stages of infection, stopping invading microbes and preventing their spread. Additionally, it helps to activate and guide the adaptive immune response, which provides more targeted and long-lasting protection against future exposure to the same pathogen.
  • Adaptive immunity: a specific immune response that develops over time after exposure to a particular pathogen. It is identified by the production of antibodies and the establishment of immune memory that enables the immune system to recognize and respond more efficiently to future exposure to the same pathogen. Adaptive immunity recognizes specific antigens, which are unique molecules on the surface of a pathogen that activate an immune response. Key components of adaptive immunity are B and T cells, with B cells generating antibodies that bind and neutralize specific antigens, and T cells directly attacking infected cells or aiding in the activation of other immune cells. Adaptive immunity is essential in defending the body against a wide range of pathogens like viruses, bacteria, and parasites. Vaccines help stimulate the adaptive immune response, providing a safe way to develop immune memory without the hazards of natural infection. Adaptive immunity provides targeted and long-lasting protection against particular pathogens, allowing the body to better fight against future exposure.

Disorders of the immune system

An overactive immune system is present in the following disorders:

  • Allergy to insects, medications, and food (urticaria, anaphylaxis, eczema, dermatitis, and so on).
  • Autoimmune disease (systemic lupus erythematosus, multiple sclerosis, diabetes, autoimmune thyroid disease, rheumatoid arthritis).

An underactive immune system is present in the following:

  • Primary immunodeficiency disease (Severe combined immunodeficiency disease - SCID, complement deficiency, common variable immunodeficiency disease - CVID).
  • Disease-induced immunodeficiency (HIV / AIDS, cancer).
  • Medication-induced immunodeficiency (chemotherapy, corticosteroids).
  1. Innate immune system
  2. Adaptive immunity
  3. Mechanisms of over-activated innate immune system regulation in autoimmune and neurodegenerative disorders
  4. The immune system
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