Understanding the Immune System: Innate and Adaptive Defenses

4 Types of Symbiosis. : Mutualism: both symbionts benefit from their interaction. EX: bacteria in your colon Worm describes another mutualistic relationship. Commensalism: one symbiont benefits without significantly affecting the other. EX: microscopic animals—hair follicle mites—live on your skin without causing measurable harm to you. Amensalism: one symbiont is harmed by a second symbiont, while the second is neither harmed nor helped by the first. EX: the fungus Penicillium produces penicillin, which inhibits nearby bacteria, but the bacteria have no effect on the fungus. Parasitism: A parasite derives benefit from its host while harming it, though some hosts sustain only slight damage. In the most severe cases, a parasite kills its host. EX: Tuberculosis bacteria in human lungs. A parasite: organism that lives on or within another organism (the host) and derives nutrients at the host’s expense. Parasites can harm their hosts but do not always cause disease. They are categorized into endoparasites, which live inside the host (e.g., tapeworms in animal intestines), and ectoparasites, which live on the host’s surface (e.g., lice on mammal skin). The host provides nourishment and shelter to the parasite and can suffer negative effects, such as weakening, disease, or other harm. Hosts can include humans, animals, plants, or microorganisms. For example, humans can host parasites like the malaria-causing Plasmodium or intestinal worms. A pathogen: organism, often a microbe, that causes disease in its host. While pathogens can be parasites, not all parasites are pathogens. Pathogens include bacteria, viruses, fungi, and protozoa that infect and cause disease. They often invade the host’s body, evade the immune system, and cause harm through mechanisms like toxin production or tissue destruction. An example is the bacterium Mycobacterium tuberculosis. Resident Microbiota: Permanent members of the microbiome found on skin and on the mucous membranes of the digestive tract, upper respiratory tract, urethra, and vagina. Most are commensal: feed on excreted cellular waste. EX: Fusobacterium (UR), Actinomyces (UD), Bacteroides (LD) Transient Microbiota: Temporary residents that come and go. may include potential pathogens or benign microorganisms. Can be influenced by: diet, hygiene, and exposure to different environments. 3 conditions that create opportunities for normal microbiota cause disease. Immunosuppression, Disruption of Normal Flora, Changes in Environment  3 types of reservoirs of infection in humans : Human Reservoirs: Infected individuals who may or may not show symptoms can serve as reservoirs for pathogens. They can transmit the disease to others through direct contact, airborne particles, or other means. : Animal Reservoirs (Zoonoses): Animals can harbor pathogens that can be transmitted to humans. Examples include rabies from dogs, Hantavirus from rodents, and avian influenza from birds. Environmental Reservoirs: Certain pathogens can survive in non-living environments such as soil, water, or surfaces. For instance, Clostridium tetani, the causative agent of tetanus, can persist in soil. Contamination: refers to the mere presence of microbes in or on the body. Does not necessarily result in infection, as the immune system may prevent the organisms from causing harm. Infection: occurs when microorganisms successfully invade host tissues, Not all infections lead to disease; an infection becomes a disease when it results in noticeable symptoms or damage to the host. Portals pathogens invade body. Skin: Intact skin is a formidable barrier, but pathogens can enter through cuts, abrasions, or insect bites. Mucous Membranes: found in the respiratory, gastrointestinal, and urogenital tracts. Can enter the body via inhalation, ingestion, etc. Placenta: Certain pathogens can cross the placental barrier from mother to fetus, potentially causing congenital infections. Parenteral Route: Pathogens can be introduced directly into tissues through punctures, injections bypassing usual barriers. Adhesion factors and play in infection: (Adhesion disks in some protozoa and suckers and hooks in some helminths) Viruses and bacteria use surface lipoproteins or glycoproteins, called ligands, to bind to complementary receptors on host cells. In bacteria, these ligands are known as adhesins, found on fimbriae, flagella, and glycocalyces. Host cell receptors are typically glycoproteins, such as mannose or galactose. Blocking or altering ligands or receptors can prevent infection. Bacteria and viruses that lose the ability to produce ligands become avirulent -harmless. Contamination: refers to the mere presence of microbes in or on the body. Does not necessarily result in infection, as the immune system may prevent causing harm. Infection: This occurs when microorganisms successfully invade host tissues, cause response.

Portals pathogens invade body. Skin Mucous Membranes: These are found in the respiratory, gastrointestinal, and urogenital tracts. Placenta, Parenteral Route: punctures, bypassing the usual barriers. Adhesion factors and roles they play in infection: (Adhesion disks in some protozoa and suckers and hooks in some helminths) Viruses and bacteria use surface lipoproteins or glycoproteins, called ligands, to bind to complementary receptors on host cells. In bacteria, these ligands are known as adhesins, found on fimbriae, flagella, and glycocalyces. Host cell receptors are typically glycoproteins, such as mannose or galactose. Blocking or altering ligands or receptors can prevent infection. Bacteria and viruses that lose the ability to produce ligands become avirulent -harmless. Biofilm may facilitate contamination and infection: A biofilm is a structured community of microorganisms encapsulated in a self-produced extracellular matrix. They facilitate contamination and infection by: Providing a Protective Environment: The extracellular matrix shields microbes from antibiotics and the immune system. Enabling Communication: Microorganisms within a biofilm can communicate through quorum sensing Promoting Persistent Infections: Biofilms can harbor persistent cells that are resistant to treatment, leading to chronic infections. Compare and contrast: Infection: The invasion of a pathogen. Infection does not always lead to disease. Disease results only if the pathogen multiplies sufficiently to adversely affect the body. Morbidity: state of being diseased, any change from a state of health. Pathogenicity: The ability of a microorganism to cause disease. It indicates whether an organism can produce disease. Virulence: The degree of pathogenicity, or the severity of the disease caused by a pathogen. Contrast: Symptoms: subjective characteristics of a disease that can be felt by the patient alone EX: PAIN Signs: objective manifestations of disease that can be observed or measured by others Syndromes: A collection of signs and symptoms that occur together and characterize a specific disease or condition. Define: Etiology is the study of the cause or origin of a disease. It involves identifying the factors and mechanisms that lead to the development of a disease. Koch’s postulates: Koch’s Postulates are a set of criteria established by Robert Koch to identify the causative agent of a disease: The microorganism must be present in all cases of the disease and absent in healthy individuals. It must be isolated and grown in pure culture. The cultured microorganism should cause disease in a healthy, susceptible host. The microorganism must be re-isolated from the experimentally infected host and identified as the same as the original causative agent. Function: To identify the causative agents of diseases. Limitations: Not all microorganisms can be cultured; some diseases are caused by multiple pathogens; asymptomatic carriers exist; ethical concerns limit testing in humans. How microbial extracellular enzymes.. affect virulence: Extracellular Enzymes: These enzymes, such as hyaluronidase and collagenase, break down host tissues, facilitating invasion and spread of pathogens. Toxins: Exotoxins are secreted, while endotoxins are components of the bacterial cell wall released upon lysis. Adhesion Factors: Molecules that enable pathogens to attach to host cells, which is a crucial step in colonization and infection establishment. Antiphagocytic Factors: help pathogens evade phagocytosis by immune cells. Ex: capsules that inhibit engulfment 5 stages of infectious diseases. 1. Incubation Period: The time between exposure to the pathogen and the onset of symptoms. 2. Prodromal Period: The onset of mild, non-specific symptoms 3. Illness: symptoms are most severe. 4. Decline: symptoms begin to subside 5. Convalescence: recovery phase Contrast; Contact Transmission: Involves direct physical contact, indirect contact via fomites (objects or surfaces), or droplet transmission (coughing, sneezing). Vehicle Transmission: spread of pathogens through a medium such as water, food, or air. Vector Transmission: transfer of pathogens via a living organism (vector). Vectors can be mechanical (e.g., flies carrying pathogens on their bodies) or biological (e.g., mosquitoes transmitting malaria). Contrast: Droplet Transmission: spread of pathogens via large respiratory droplets expelled during coughing, sneezing, or talking. Airborne Transmission: spread of pathogens via smaller respiratory droplets or dust particles

Second line of defense: Inflammation, Monocytes, Lactoferrin, Fever, Alpha interferon, Neutrophils, Phagocytes First line of defense: Dendritic cells, Mucous membrane of the digestive tract, Epidermis, Lysozyme, Goblet cells, Sebum, Antimicrobial peptides Third line of defense: T-lymphocytes

-Chemotactic factors, such as chemicals called chemokines, attract phagocytic leukocytes to the site of damage or invasion. Phagocytes attach to pathogens via a process called adhesion.