Immunology

• Immune response is a response generated against a potential pathogen.
• The first line of defense, which is nonspecific to the invading pathogen, is rapidly mobilized at the initial site of infection but lacks immunologic memory and is called innate immunity.
• The second defense system is called adaptive immunity . It is specific for the pathogen and can confer protective immunity to reinfection with that pathogen.
• Adaptive immunity can specifically recognize and destroy the pathogen because of lymphocytes carrying specialized cellular receptors and specific antibodies.
• A protein that is produced in response to a particular pathogen is called antibody , and the substance that induces the production of antibodies is called the antigen
• Antibodies are proteins secreted by B cells (B-lymphocytes) into circulation or onto mucosal surfaces where they bind to foreign substances such as bacteria, viruses, parasites, and other microorganisms.
• Antigens may be large molecules like polysaccharides, glycoproteins, lipoproteins, nucleic acids, or small molecules like haptenes.
• Innate immunity is an immediate response to the pathogen that does not confer long-lasting protective immunity
• Lysozyme, an enzyme that dissolves some bacterial cell walls, is present on the skin and can help provide protection against some microorganisms.
• The skin produces a variety of antimicrobial agents, including a protein with antibacterial properties known as psoriasin.
• The mucociliary apparatus for removal of bacteria in the respiratory tract is aided by the pulmonary macrophages
• Special protective mechanisms in the respiratory tract include the hairs at the nares and the cough reflex, which prevents aspiration.
• Bacterial interference is when a normal microbiota opposes establishment of pathologic microorganisms.
• Innate immunity system has both cells and cytokines at its disposal. Phagocytic leukocytes, such as polymorphonuclear neutrophilic leukocytes (PMNs) and macrophages along with natural killer (NK) cells are the primary cellular components to combat microbes.
• Primary cellular components of innate immunity to combat microbes

  Phagocytic leukocytes such as OMNs, macrophages and NK cells
• Three major groups of microbial sensors: (1) TLRs, (2) NOD-like receptors (NLRs), and (3) RIG-1 like helicases and MDA-5.
• The main functions of phagocytic cells include chemotaxis, migration, ingestion, and microbial killing.
• Phagocytes in the immune system consist of (1) monocytes and macrophages; (2) granulocytes, including PMNs, eosinophils, and basophils; and (3) dendritic cells.
• Monocytes are small leukocytes that circulate in the blood and mature into macrophages that can be found in almost all tissues
• Granulocytes are leukocytes that contain densely staining granules
• PMNs have a short half-life and are important phagocytic cells that destroy pathogens within intracellular vesicles
• Eosinophils and basophils are less abundant and contain granules containing enzymes and toxic proteins that can be released upon activation of the cells.
• Dendritic cells are phagocytic and can degrade pathogens; however, their main role is to activate T cells in the adaptive immune response by acting as antigen-presenting cells (APCs) and by producing regulatory cytokines.
• Phagocytosis is the process whereby a phagocytic cell, especially the PMN, recognizes the pathogen, ingests it, and then destroys the engulfed organism