System Day 1and 2 AI Question Immune System Fundamentals

Immune System

• The immune system is the body's defense against foreign invaders, providing protection from disease and infectious disease.
• Immunity is based on the capacity to recognize foreign invaders (non-self).

Microbes and Antigens

• A microbe is a type of microorganism that is too small to see with the unaided eye, such as bacteria, viruses, and fungi.
• A microbe that causes disease is called a pathogen.
• An antigen is a large molecule (usually a protein or polysaccharide) on a cell surface that elicits a specific response from the host.
• An epitope is a part of an antigen molecule to which an antibody attaches.

Immune Response

• The immune response is the collective, coordinated response of the cells and molecules of the immune system to protect against infectious disease.
• There are two types of immune responses: innate and adaptive.

Innate Response

• The innate response is a non-specific, initial line of defense that provides an effective barrier to microbes.
• It is something we are born with and is the first line of defense against infection.

Adaptive Response

• The adaptive response is a specific response that develops with exposure to various organisms and substances that the immune system finds threatening.
• It is very effective and involves the activation of immune cells, such as B-cells and T-cells.

B-Cells and T-Cells

• B-cells (B-lymphocytes) are key players in humoral immunity, recognizing microbes and antigens, and producing antibodies.
• T-cells (T-lymphocytes) are responsible for cell-mediated/cellular immunity and work via cell-to-cell contact or by secreting messenger compounds that communicate with immune system cells.

Types of T-Cells

• T-Helper cells (CD-4 cells) upregulate and are key regulatory cells of the immune system.
• Regulatory T-cells (Tregs) downregulate and suppress/modify immune responses.
• T-cytotoxic cells (CD-8 cells) destroy identified/presented antigens and kill virus-infected cells.

Antigen Presenting Cells

• These cells bind to and/or break down antigens and present epitopes on their surfaces, or alter the antigen to make it more recognizable.

Humoral Immunity and Immunoglobulins

• Humoral immunity involves the production of antibodies by B-cells.
• There are different types of immunoglobulins (Ig), such as IgG, IgA, and IgM, each with specific functions.

Active and Passive Immunity

• Active immunity develops through direct exposure to an antigen.
• Passive immunity is passed from a mother to fetus, or injected from one system to another.

Autoimmune Diseases

• Immunologic self-tolerance is the ability to distinguish between self- and non-self antigens.
• Autoimmune diseases, such as Rheumatoid Arthritis, Multiple Sclerosis, and Myasthenia Gravis, occur when the immune system mounts a response against the body's own tissues.

Hypersensitivity Disorders

• Hypersensitivity disorders occur when the immune system overreacts to antigens, leading to inflammation and tissue damage.
• There are four types of hypersensitivity reactions: Type I (Immediate), Type II (Antibody-mediated), Type III (Immune Complex-mediated), and Type IV (Delayed or Cell-mediated).

Type I Hypersensitivity

• Mediated by IgE, leading to the release of inflammatory mediators from sensitized mast cells.
• Examples include allergic rhinitis, asthma, urticaria, angioedema, and gastrointestinal food allergies.

Type II Hypersensitivity

• Mediated by IgM or IgG, directed against target antigens on cell surfaces or in extracellular tissue.
• Examples include hemolysis, erythroblastosis fetalis, autoimmune hemolytic anemia, blood transfusion reactions, and autoimmune thrombocytopenia.

Type III Hypersensitivity

• Mediated by the formation of antigen-antibody complexes, complement fixation, and localized inflammation.
• Examples include the Arthus reaction, serum sickness, glomerulonephritis, and polyarteritis nodosa.

Type IV Hypersensitivity

• Mediated by specifically sensitized T-lymphocytes, manifesting as sub-acute or chronic inflammation.
• Examples include contact dermatitis and graft rejection.