Understanding the Immune System and Infectious Diseases

• The immune system defends the body against infections and diseases caused by harmful germs like bacteria and viruses
• It comprises different cells, tissues, and organs that work in coordination
• The immune system distinguishes between the body's own cells and foreign invaders, targeting only harmful ones
• It employs general defenses, such as skin barriers, and specific responses using special cells like T cells and B cells
• T and B cells help destroy germs and "remember" them for faster responses upon re-exposure
• This system helps maintain health and fights illnesses

What Causes Infectious Diseases

• Pathogens, tiny organisms, lead to sickness
• These organisms may include bacteria, viruses, fungi, and parasites.
• Bacteria are small, single-celled organisms causing diseases like strep throat or food poisoning
• Viruses, smaller than bacteria, need a living cell to grow and can cause illnesses like flu or COVID-19
• Fungi, including molds and yeasts, can cause infections like athlete's foot
• Parasites live on or inside another organism, causing diseases like malaria
• Infectious diseases arise when these pathogens invade the body, causing you to feel unwell

Types of Pathogens

• Cellular (Living)
  • Parasites
  • Protozoa
  • Fungi
  • Prokaryote
• Acellular (Non-Living)
  • Virus
  • Prion

The Role of Antigens in Identifying Self vs. Non-Self

• Antigens are special markers on cell surfaces that help the immune system distinguish between the body's own cells and foreign entities
• The body's cells have unique antigens, identifying them as "self"
• Foreign pathogens such as bacteria or viruses possess different antigens, recognized as "non-self"
• Recognition of non-self antigens triggers an immune response
• The immune system activates specific cells to attack and eliminate the foreign pathogens

Non-Specific (Innate) Immunity

• Innate immunity serves as the body's initial defense against infections

• This immunity responds rapidly to a wide array of harmful invaders, including bacteria, viruses, and fungi

• Targeting no specific pathogens, it provides general protection against any foreign threat

• Key components of non-specific immunity that keep us healthy

  • Skin acts as a physical barrier that prevents microorganisms from entering
  • Skin produces antimicrobial substances in oils and sweat
  • Tears, containing enzymes, protect eyes, and remove potentially harmful substances, are an important defense
  • Saliva contains enzymes to break down bacterial cell walls
  • Stomach acid destroys many microorganisms
  • Phagocytes (macrophages) are specialized white blood cells that engulf and digest harmful microorganisms

• Inflammation, another non-specific immune response, occurs when tissues are injured or infected

• Blood flow increases to the affected area, bringing more immune cells to fight infection and promote healing

• Fever can occur, raising body temperature to create an unfavorable environment for pathogens and improve immune cell effectiveness

Specific (Adaptive) Immunity

• Adaptive immunity, unlike non-specific immunity, is a targeted response to specific pathogens, developing over time
• This part involves specialized cells called lymphocytes (T cells and B cells)
• When a pathogen enters the body, T and B cells identify unique antigens and prepare a specific response
• The process
  • Macrophages engulf and digest pathogens, presenting pieces (antigens) on their surface
  • Macrophages present antigens to helper T cells, which activate and multiply upon recognition of a specific antigen
  • Activated helper T cells release cytokines, activating B cells to grow and divide
  • B cells produce antibodies specific to the pathogen
  • Helper T cells stimulate killer T cells to identify and destroy infected or abnormal cells displaying the pathogen's antigens
  • B cells release antibodies to bind pathogens, marking them for destruction
  • Killer T cells seek out and destroy infected cells
• After an infection clears, some B cells become memory cells
  • Memory B cells retain information about the specific pathogen for a quicker, stronger response if it reappears

The Power of Modern Medicine

• Antibiotics, antivirals, antifungals, antiparasitics, and vaccines treat infections caused by different types of pathogens
• Antibiotics combat bacterial infections by killing bacteria or stopping their growth, effective against diseases like strep throat and pneumonia
• Antivirals treat viral infections by stopping viruses from multiplying, managing symptoms and reducing severity, but not curing the infection itself
• Antifungals treat fungal infections by killing or stopping the growth of fungal cells, combating conditions like athlete's foot and yeast infections
• Antiparasitics target parasitic infections and treat diseases like malaria and giardiasis by eliminating parasites
• Vaccines prevent infections by helping the immune system recognize and fight specific pathogens, preventing both bacterial and viral infections
• Vaccines introduce a harmless part of the pathogen into the body, prompting the immune system to build antibody defenses

Innate vs Adaptive Immunity

• Innate and adaptive immunity function at different speeds
• Innate immunity acts fast, in minutes to hours, involving barriers like skin and phagocytes that attack many pathogens
• Adaptive immunity takes longer, days to weeks, involving specific immune cells (T and B cells) that recognize particular pathogens
• Adaptive immunity results in antibodies and memory cells, enabling faster response upon re-infection
• Innate immunity is quick and broad, while adaptive immunity is slower, more targeted, and lasting

Explore the immune system's role in defending the body against infections and diseases. Learn about pathogens like bacteria, viruses and fungi, and how they cause illness. Understanding the difference between bacteria and viruses and their impact on health.