Immune system

•  all lymphocytes (white blood cells)  originate in the bone marrow, only B cells remain in the bone marrow to complete maturation. 
• dentical twins have the same MHC molecules and can easily accept transplants of tissues from each other.
• major histocompatibility complex (MHC) of genes consists of a linked set of genetic loci encoding many of the proteins involved in antigen presentation to T cells,
• Pathogen → Organism that is detrimental to its host. The body does not recognize it.
• Skin and mucus membranes → First line of defense against pathogens→ Non specific ( not selective about what it blocks from getting into the body)
• Inflammatory response→ Part of the second line of defense → Includes phagocytic white cells and mast cells 
• Mast cells : Assist with allergic and inflammatory responses → Contain histamine, which causes blood vessels to dilate and leak
• Dilation and leakiness allow macrophages (white blood cells) to reach the pathogens easier.
• Macrophages engulfs and digest pathogens→ Un antigen from the pathogen rises to the surface. 
• Complement system → Help or complement the actions of the immune system. 
• Nonspecific responses → Generalized response to pathogen infections involving the use of several white blood cells and plasma 
• Adaptive immunity → specific response to an antigen
• Cell mediated → 3rd line of response → Cytotoxic cell 
• Cytotoxic T cell (white blood cell) → Destroys infected cells → Part of the cell mediated response. Releases perforin (a protein) that causes the infected cell to do apoptosis (cell death) → Destroy the infected cell and destroy the pathogen or make the pathogen unable to continue to reproduce 
• T helper cell → Los patógenos que son previamente engulfed by the macrophages pasan a la superficie, la helper T cell releases chemical signals that stimulate cytotoxic T cells.
• Helper T cells → 3rd line of defense → Activate other whit blood cells → Part of the cell mediated and humoural responses. 
• Humoral response → Los patógenos que son previamente engulfed by the macrophages pasan a la superficie, la helper T cell releases chemical signals that stimulate B cells. → Very involved in memory 
• B cells → 3rd line of defense → white blood cells → Ability to make antibodies→ 
• Antigen→ Something that the immune system recognizes as something foreign
• Antibiotics→ Substances that can specifically destroy bacteria. 
• Antibodies→ Proteins (Y shape) → Have an antigen binding area where they bind an specific antigen. → Found in blood → Very specific→ When antibodies bind to an antigen they can deactivate the pathogen  by affecting the ability of the pathogen to move, reproduce or cause harm. 
• Memory cells → 3rd line of defense → Stores “memory of pathogens” → Part of the humoral and cell-mediated response. 
• Memory B cells activate→ Plasma B cells → Antibodies 
• Memory T cells activate → Plasma T cells→ Cytotoxic T cells that destroy infected cells. 
• Natural killer cells are part of innate immunity. 
• Agglutination→ antibodies have more than one binding site. Can bind to multiple antigens