The immune system protects the body from possibly harmful substances by recognizing and responding to antigens. Antigens are substances (usually proteins) on the surface of cells, viruses, fungi, or bacteria. Nonliving substances such as toxins, chemicals, drugs, and foreign particles (such as a splinter) can also be antigens. The immune system recognizes and destroys, or tries to destroy, substances that contain antigens. Your body's cells have proteins that are antigens. These include a group of antigens called HLA antigens. Your immune system learns to see these antigens as normal and usually does not react against them.
Innate, or nonspecific, immunity is the defense system with which you were born. It protects you against all antigens. Innate immunity involves barriers that keep harmful materials from entering your body. These barriers form the first line of defense in the immune response. Examples of innate immunity include:
Enzymes in tears and skin oils
Mucus, which traps bacteria and small particles
Innate immunity also comes in a protein chemical form, called innate humoral immunity. Examples include the body's complement system and substances called interferon and interleukin-1 (which causes fever). If an antigen gets past these barriers, it is attacked and destroyed by other parts of the immune system. Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense against that specific antigen. Passive immunity is due to antibodies that are produced in a body other than your own. Infants have passive immunity because they are born with antibodies that are transferred through the placenta from their mother. These antibodies disappear between ages 6 and 12 months. Passive immunization may also be due to injection of antiserum, which contains antibodies that are formed by another person or animal. It provides immediate protection against an antigen, but does not provide long-lasting protection. Immune serum globulin (given for hepatitis exposure) and tetanus antitoxin are examples of passive immunization.
Antigens are substances (usually proteins) on the surface of cells, viruses, fungi, or bacteria. ... Your immune system learns to see these antigens as normal and usually does not react against them. INNATE IMMUNITY. Innate, or nonspecific, immunity is the defense system with which you were born
Specific immune system gets activated when the pathogens (foreign elements) enter the body and are able enough to bypass the innate immune defenses thereby activating the adaptive immune system
Specific defense is triggered by elements found on the surface of pathogens. These surface elements are called antigens. Antigens responds to these pathogens by producing antibodies specific to pathogen surface type.
Actually, in physical cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. About first millisecond, the universe had cooled to a few trillion kelvins (1012 K) and quarks finally had the opportunity to bind together into free protons and neutrons. Free neutrons are unstable with a half-life of about ten minutes (614.8 s) and formed in much smaller numbers. The abundance ratio was about seven protons for every neutron. Before one neutron half-life passed nearly every neutron had paired up with a proton, and nearly every one of these pairs had paired up to form helium. By this time the universe had cooled to a few billion kelvins (109 K) and the rate of nucleosynthesis had slowed down significantly.