Immune Cells PDF

1. Innate Immune Cells: o First responders; non-specific and fast-acting. o Provide general defense against any invader. 2. Adaptive Immune Cells: o Specific and targeted; slower to respond initially but have memory for future encounters....

1. Innate Immune Cells: o First responders; non-specific and fast-acting. o Provide general defense against any invader. 2. Adaptive Immune Cells: o Specific and targeted; slower to respond initially but have memory for future encounters. o Provide long-term immunity. 2. Innate Immune Cells and Their Functions A. Neutrophils  Description: The most abundant white blood cells in the bloodstream.  Function: o First responders to infection or injury. o Phagocytose (engulf and digest) pathogens and debris. o Release enzymes and reactive oxygen species to kill invaders.  Lifespan: Short-lived (hours to a few days).  Fun Fact: Pus in a wound is made up largely of dead neutrophils. B. Macrophages  Description: Large, long-lived phagocytes derived from monocytes.  Function: o Engulf and digest pathogens, dead cells, and debris. o Act as antigen-presenting cells (APCs) by displaying digested pathogen fragments on MHC Class II molecules to T-cells. o Release cytokines to recruit more immune cells.  Locations: o Found in tissues (e.g., Kup er cells in the liver, microglia in the brain). C. Dendritic Cells   Description: Highly specialized antigen-presenting cells.  Function: o Patrol tissues and engulf pathogens. o Process and present antigens to naïve T-cells in lymph nodes, kickstarting the adaptive immune response. o Bridge the innate and adaptive immune systems.  Fun Fact: Known as "professional antigen-presenting cells" due to their e iciency. D. Natural Killer (NK) Cells  Description: Cytotoxic lymphocytes that act independently of antigen presentation.  Function: o Kill virus-infected cells or cancerous cells by releasing perforin (creates pores in target cells) and granzymes (trigger apoptosis). o Detect cells that have downregulated MHC Class I molecules (a common trick by viruses to evade detection).  Unique Feature: Unlike T-cells, they don’t require prior activation or antigen presentation. E. Eosinophils  Description: Granulocytes involved in responses to parasites and allergens.  Function: o Release toxic granules to kill parasites like helminths (worms). o Contribute to allergic reactions by releasing inflammatory mediators.  Fun Fact: Elevated eosinophil levels are often seen in parasitic infections and allergies. F. Basophils  Description: Rare granulocytes involved in inflammatory and allergic responses.   Function: o Release histamine, promoting inflammation and recruiting other immune cells. o Play a role in allergic reactions, similar to mast cells. G. Mast Cells  Description: Found in tissues, especially near blood vessels and mucosal surfaces.  Function: o Release histamine and other inflammatory chemicals during allergic reactions or infection. o Involved in wound healing and defense against parasites.  Fun Fact: Responsible for the symptoms of hay fever and other allergic reactions. 3. Adaptive Immune Cells and Their Functions A. Lymphocytes Lymphocytes are the backbone of the adaptive immune system. They include B-cells, T- cells, and Natural Killer (NK) cells. B. B-Cells  Description: Produced in the bone marrow and mature there.  Function: o Antibody Production: When activated, B-cells become plasma cells and secrete antibodies specific to a pathogen’s antigens. o Memory B-Cells: After an infection, some B-cells remain as memory cells, providing long-term immunity.  Fun Fact: Each B-cell produces antibodies specific to one type of antigen, like a lock and key. C. T-Cells T-cells are produced in the bone marrow and mature in the thymus. They are divided into di erent types based on their functions: 1. Helper T-Cells (CD4+ T-Cells): o Function:  Coordinate the immune response by releasing cytokines.  Activate B-cells to produce antibodies.  Help cytotoxic T-cells and macrophages function e ectively. o Fun Fact: These are the cells targeted by HIV. 2. Cytotoxic T-Cells (CD8+ T-Cells): o Function:  Kill infected cells or cancer cells directly.  Recognize antigens presented on MHC Class I molecules. o Mechanism:  Release perforin and granzymes to induce apoptosis in infected cells. 3. Regulatory T-Cells (Tregs): o Function:  Suppress overactive immune responses to prevent autoimmunity.  Ensure the immune system doesn’t attack healthy tissues. o Fun Fact: Sometimes called "peacekeeper" cells. 4. Memory T-Cells: o Function:  Remain in the body after an infection to mount a faster and stronger response if the same pathogen reappears. 4. Other Immune Cells Monocytes:  Description: Precursors to macrophages and dendritic cells.  Function:  o Circulate in the blood and migrate to tissues to di erentiate into macrophages or dendritic cells. Plasma Cells:  Description: Fully activated B-cells.  Function: o Produce large amounts of antibodies specific to a pathogen. Memory Cells:  Description: Specialized T-cells and B-cells that "remember" a pathogen.  Function: o Provide long-lasting immunity by responding rapidly during future infections.. How Do Vaccines Work? The goal of a vaccine is to create immunity. Here’s the process: A. Exposure to Antigens Vaccines contain antigens, which are harmless fragments or versions of a pathogen (like a virus or bacteria). These antigens mimic the pathogen but cannot cause the disease. When introduced into your body:  The immune system identifies the antigens as foreign (non-self).  This triggers an immune response, just as it would if you were exposed to the actual disease. B. Activation of the Immune System 1. Antigen Presentation: o Antigens from the vaccine are "picked up" by antigen-presenting cells (APCs) like macrophages or dendritic cells. o These APCs present the antigens on their MHC molecules to T-cells in lymph nodes. 2. T-Cell Activation: o Helper T-Cells (CD4+ T-cells): Signal and coordinate the immune response by activating other immune cells.  o Cytotoxic T-Cells (CD8+ T-cells): Learn to recognize infected cells and destroy them. 3. B-Cell Activation: o B-cells, activated by T-cells, produce antibodies specific to the pathogen's antigens. o Antibodies neutralize the pathogen or mark it for destruction by other immune cells. C. Creation of Memory Cells After the immune response, the body produces memory B-cells and memory T-cells that "remember" the specific pathogen. If the real pathogen enters your body in the future:  These memory cells recognize it immediately.  They mount a faster and stronger immune response, often preventing illness altogether. 2. Types of Immunity from Vaccines Vaccines provide active immunity, meaning your body produces its own antibodies and memory cells. This is di erent from passive immunity, where you receive pre-made antibodies (e.g., through breastfeeding or antibody therapy). 3. Types of Vaccines There are several types of vaccines, each designed di erently to suit the characteristics of specific diseases: A. Inactivated (Killed) Vaccines  Contain pathogens that have been killed or inactivated so they cannot replicate or cause disease.  Examples: Polio vaccine (IPV), Hepatitis A vaccine.  Advantages: o Safe for people with weakened immune systems.  Disadvantages: o May require booster shots for long-term immunity. B. Live Attenuated Vaccines  Contain live pathogens that have been weakened (attenuated) so they cannot cause serious disease.  Examples: Measles, mumps, and rubella (MMR) vaccine; Chickenpox vaccine.  Advantages: o Strong and long-lasting immunity.  Disadvantages: o Not safe for people with weakened immune systems. C. Subunit, Recombinant, or Conjugate Vaccines  Contain only specific parts of the pathogen, such as proteins, sugars, or capsid fragments.  Examples: Human papillomavirus (HPV) vaccine, Hepatitis B vaccine.  Advantages: o Very safe because they don’t contain live pathogens.  Disadvantages: o May require multiple doses. D. Toxoid Vaccines  Contain inactivated toxins (toxoids) produced by bacteria.  Examples: Tetanus vaccine, Diphtheria vaccine.  Advantages: o Protect against bacterial toxins.  Disadvantages: o May require booster shots. E. mRNA Vaccines   Use a piece of messenger RNA (mRNA) to instruct cells to produce a harmless protein from the pathogen. This protein triggers an immune response.  Examples: COVID-19 vaccines (Pfizer-BioNTech, Moderna).  Advantages: o Quick to develop and manufacture. o Do not contain live virus.  Disadvantages: o Requires cold storage for stability. F. Viral Vector Vaccines  Use a harmless virus (like adenovirus) as a "vector" to deliver genetic material from the pathogen to your cells, prompting an immune response.  Examples: Johnson & Johnson COVID-19 vaccine, Ebola vaccine.  Advantages: o Strong immune response.  Disadvantages: o Potential for rare side e ects. 4. How Do Boosters Work?  Some vaccines require booster doses because immunity can wane over time.  A booster "reminds" the immune system of the pathogen, prompting memory cells to re-activate and strengthen immunity. 5. Herd Immunity: Protecting the Community Vaccines don’t just protect individuals; they also protect the community. Herd immunity occurs when enough people are vaccinated, making it di icult for the disease to spread. This is crucial for protecting those who cannot be vaccinated (e.g., people with allergies or weakened immune systems). 6. Vaccine Safety Vaccines undergo rigorous testing for safety and e icacy before being approved. The process includes: 1. Preclinical Testing: Laboratory and animal studies. 2. Clinical Trials: o Phase 1: Tests safety and dosage on a small group of people. o Phase 2: Tests e icacy and side e ects on a larger group. o Phase 3: Tests on thousands of people to confirm e ectiveness and monitor rare side e ects. 3. Post-Market Surveillance: Continuous monitoring after the vaccine is approved. 7. Common Misconceptions 1. “Vaccines cause the disease they prevent.” o Most vaccines don’t contain live pathogens, and those that do are attenuated (weakened) to prevent disease. 2. “Vaccines cause autism.” o Extensive studies have found no link between vaccines and autism. 3. “If others are vaccinated, I don’t need to be.” o Herd immunity only works when most people are vaccinated. Without widespread vaccination, outbreaks can occur. 8. Summary Vaccines work by introducing harmless parts or versions of a pathogen to your immune system. This allows your body to "practice" fighting the pathogen, so if you’re exposed to the real thing, your immune system can respond quickly and e ectively. They’re safe, e ective, and one of the greatest advancements in public health.