• Fever is a symptom of an anti-infection defense mechanism that appears with body temperature exceeding the normal range due to an increase in the body's temperature.
  
  
• Mechanical barriers — which include the skin, mucous membranes, and fluids such as tears and urine — physically block pathogens from entering the body. Chemical barriers — such as enzymes in sweat, saliva, and semen — kill pathogens on body surfaces.
  
  
• Antibodies or immunoglobin are protective proteins produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and latch onto antigens in order to remove them from the body.
  
  
• The receptors usually recognize components of microorganisms that are not found on cells of the host, e.g. components of bacterial cell wall, bacterial flagella or viral nucleic acids.
  
  
• The thymus is a small gland in the lymphatic system that makes and trains special white blood cells called T-cells. The T-cells help the immune system fight disease and infection. The thymus gland produces most of your T-cells before birth.
  
  
• Phagocytosis is the process by which certain living cells called phagocytes ingest or engulf other cells or particles. It is defensive reaction against infection and invasion of the body by foreign substances (antigens).
  
  
• Inflammation is a protective response involving immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out damaged cells and tissues, and initiate tissue repair.
  
  
• The lymphatic system is a subsystem of the circulatory system in the vertebrate body that consists of a complex network of vessels, tissues, and organs. It helps defend the body against infection by supplying disease-fighting cells called lymphocytes.
  
  
• Messenger molecules
  
  
• Agglutination, is the clumping of red blood cells within the body. It is the body's natural immune response to toxins and pathogens. When red blood cells meet toxins and pathogens within the body, they clump them together.
  
  
• Peptides
  
  
• Memory cells are white blood cells that help the immune system recognize and fight specific pathogens. They are produced after the body encounters a pathogen, and they remain in the immune system to help the body fight the pathogen again.
  
  
• Immunological memory is the ability of the immune system to respond more quickly and effectively to pathogens it has encountered before.
  
  
• B-plasma cells are a type of white blood cell that makes infection-fighting proteins called antibodies.
  
  
• Cytotoxic cells are involved in directly killing intracellular and extracellular pathogens and eliminating mutated and cancerous cells.
  
  
• Helper T cells are a type of immune cell. When they sense an infection, they activate other immune cells to fight it. They may activate cytotoxic T cells or they may activate B cells, which produce antibodies.
  
  
• Antigen-presenting cells (APCs) are a large group of various cells that trigger the cellular immune response by processing an antigen and exposing it in a form recognizable by T cells in the process known as antigen presentation.
  
  

B-plasma cells, cytotoxic cells (=cytotoxic T-Lymphocytes), thymus, T helper cells (=CD4 cells), APC (=Antigen presenting cell), phagocytosis, cell clone, clonal selection, somatic recombination, autoimmune disease, Macrophage, precipitation of soluble antigens pairs of terms: innate and specific immune response, self and no self, MHCI/II, humoral and cellular immune response, primary and secondary response, activation phase and effector phase, monoclonal and polyclonal antibodies, antibody and receptor, antibody and antigen, heavy chain and light chain, active and passive immunization, B- and TLymphocytes