Overview of the Immune System

Immune System: A Wonderfully Complex Mystery

First Line of Defense • What is the body’s first line of defense? The body’s first line of defense includes physical and chemical barriers, such as the skin, mucous membranes, tears, saliva, and stomach acid. These barriers prevent pathogens from entering the body. • What is the second? The second line of defense consists of nonspecific innate immune responses, such as inflammation, fever, and the activity of phagocytes, natural killer cells, and complement proteins. • What happens to any intruders? Intruders are identified as foreign and destroyed by phagocytosis, where immune cells like macrophages engulf and digest the pathogens. • What happens when that fails? If the innate defenses fail, the adaptive immune system is activated to specifically target and eliminate the intruder through the action of B cells, T cells, and antibodies. • What does this mean for nurses? Nurses must monitor for signs of compromised immunity, such as persistent infections, and educate patients on maintaining a strong immune system through proper hygiene, vaccination, and overall health practices.

Immunity • Stress: Chronic stress can suppress immune function by increasing cortisol levels, reducing the activity of lymphocytes. • Nutrition: Adequate nutrition, including vitamins A, C, D, E, and zinc, is essential for immune cell production and function. • Inflammation: A normal immune response to injury or infection, inflammation involves redness, swelling, heat, and pain as immune cells are recruited to the affected area. • Tissue Integrity: Intact skin and mucous membranes are vital to prevent pathogen entry. • Age: Immune function declines with age, making older adults more susceptible to infections and less responsive to vaccines.

How Does the Immune System Work?

1. Invader Detected by Macrophage: Macrophages recognize and engulf foreign invaders, presenting antigens to other immune cells. o Phagocytosis: The process of engulfing and digesting pathogens. o Lysosome: Intracellular organelles that contain enzymes to break down pathogens.
2. Stem Cells: o Divide into two daughter cells; some remain as stem cells, while others differentiate into various immune cells (e.g., macrophages, neutrophils, lymphocytes). o Controlled process ensuring adequate immune cell production. o Divides into 2 daughter cells o Some return and others go on to become other cells o Not random but controlled o Stem cells will become a macrophage, neutrophil, or a WBC o Stem cell therapy

T Cells • Belong to the adaptive immune system: Produced in the bone marrow and mature in the thymus. • Body has 300 Billion • Types: o Killer T cells: Destroy virus-infected or cancerous cells by inducing apoptosis. o Helper T cells: Secrete cytokines, such as interleukin-2 and interferon-gamma, to activate other immune cells. o Regulatory T cells: Modulate immune responses to prevent overactivity and autoimmunity.

B Cells • Activated by recognizing antigens, either independently or with the help of T cells. • Produce antibodies targeting specific antigens. • Autoimmunity can occur when B cells fail to distinguish self from non-self. • Can have difficulty recognizing their own molecules, leading to production of antibodies

Antibodies • IgM: Bind to virus and prevent infecting cells - First antibody produced; activates the complement cascade. o IgM is very good at activating the complement cascade o When B cells are activated they mostly release IgM o By starting the complement cascade they are …. • IgG: Neutralize virus - Most abundant in blood; crosses the placenta to provide passive immunity to the fetus. o These antibodies can pass from mother to fetus via placenta o Protects fetus until they produce their own a few months after birth • IgA: Guards mucosa surfaces - Guards mucosal surfaces; secreted in breast milk to protect infants. o Most abundant in the body, 400 square meters of mucosal surfaces o Can cross intestinal wall, resistant to acids and enzymes o Secreted through breastmilk, coats the baby’s intestines • IgE: Bound to mast cells - Involved in allergic reactions and defense against parasites. o Charles Richet, 1913 Nobel Prize

Anaphylaxis • Mast cells degranulating: Release histamine and other inflammatory mediators, causing symptoms like swelling, hives, and difficulty breathing. • Allergens are antigens that can cause an allergic reaction: Common allergens include peanuts, shellfish, insect stings, and certain medications. • Repeated exposure, IgE antibodies which are bound to mast cells: Upon repeated exposure to an allergen, IgE antibodies trigger mast cell degranulation and systemic reactions. • What is the treatment? o Immediate administration of intramuscular epinephrine to counteract severe symptoms. o Additional treatments may include antihistamines, corticosteroids, and oxygen therapy to stabilize the patient. o Prevention involves identifying and avoiding known allergens and carrying an epinephrine auto-injector.

Adaptive System • Discovered by Edward Jenner through smallpox vaccination. • Enables the body to recognize and respond to specific antigens through B and T cells. • Antibodies tag pathogens for destruction but do not directly kill them (opsonization).

Innate System • Includes complement proteins, phagocytes, and natural killer cells. • Provides immediate, nonspecific defense against common pathogens. • Collaborates with the adaptive system to enhance immune responses. • Attacks invaders • B&T Cells can detect any molecule • Innate system makes judgement if the molecule is dangerous – therefore can recognize uncommon pathogens

Complement System • The complement system is a crucial part of the immune response, composed of proteins primarily produced by the liver. o Functions:  Opsonization: Proteins bind to pathogens, marking them for phagocytosis by immune cells such as macrophages.  Chemoattractant Activity: Complement proteins serve as signals to recruit additional immune cells to the site of infection.  Pathogen Lysis: The membrane attack complex (MAC) forms pores in pathogen membranes, leading to cell lysis. • C3 Protein: o The most abundant and central protein in the complement system. o Continuously breaks down into two smaller proteins: C3a and C3b. o C3b: Binds to the surface of pathogens, initiating the complement cascade and enhancing phagocyte attachment. • Key Roles of Complement Proteins: o Decorating pathogen surfaces to improve phagocytosis. o Serving as chemoattractants to draw immune cells like neutrophils to the infection site. • Macrophages: o Produced in the bone marrow from stem cells. o Detect invaders and secrete chemicals to increase blood flow, leading to swelling, redness, and activation of other immune cells through cytokine release. • Neutrophils: o Short-lived immune cells that make up about 70% of circulating white blood cells. o Rapidly respond to infection, leaving the bloodstream within 30 minutes of activation. o Known as "professional killers" due to their efficiency in pathogen destruction. • Natural Killer Cells: o Reside primarily in the liver and spleen, on standby to attack infected or abnormal cells. o Destroy viruses, bacteria, parasites, fungi, and tumor cells by inducing apoptosis (cell suicide).

Misguided Immune System • Tuberculosis: Immune overreaction can damage lung tissue. • Sepsis: Systemic inflammation leading to organ dysfunction. • Allergies: Overproduction of IgE in response to harmless antigens. • Autoimmune Diseases: Immune system attacks the body’s own tissues (e.g., lupus, rheumatoid arthritis). • Inflammation:

Vaccines • Stimulate the immune system to recognize specific pathogens without causing disease. • Types include: o Toxoid: Inactivated bacterial toxins (e.g., tetanus). o Attenuated: Weakened live pathogens (e.g., MMR vaccine).

Monoclonal Antibodies • Laboratory-produced antibodies targeting specific antigens, often on cancer cells. • Applications include: o Blocking cancer cell growth. o Directly attacking cancer cells. o Modulating immune responses. • Examples: Cetuximab (antibody chimera) and Otelixizumab (humanized chimera).

This quiz explores the fundamental aspects of the immune system, including its structure, function, and the distinction between innate and adaptive immunity. It delves into the body's first line of defense and the various components involved in protecting against pathogens. Test your understanding of how the immune system operates to safeguard health.