Immunology

• IgA is important in mucous.
• The physical and chemical barriers include the skin, mucosa in the nose, mouth, etc., antimicrobial proteins, and the immune system.
• The innate immune response is specific as they have a lot of receptors so they can recognize a lot of pathogens, whereas the adaptive immune system is very specific due to specific and fewer receptors.
• The innate immune system recognizes patterns and the adaptive immune system recognizes antigens, both being specific.
• The innate immune system takes action immediately and the adaptive immune system takes a couple of days, like 4-5 days.
• In the Peyer’s patch (MALT), the antigens come from the mucosa which translocates these antigens to the T-cell zone.
• Co-stimulation is provided by the binding of CD40 on the B-cell and CD40L bound to the follicular T-helper cell.
• When the B-cells are activated, they go into the secondary lymphoid follicle where there is the presence of a germinal center, which is a cluster of B-cells.
• In the lymph node, dendritic cells come through the lymph vessels and enter the lymphoid.
• The B- and T-cells will enter the lymph node through the blood vessels and will go to their assigned zones.
• The dendritic cells will go to the T-cell zone.
• Naive B-, and T-cells enter again through the bloodstream to their assigned zone and leave through the lymphatic vessels.
• A part of the activated T-cells will turn into follicular T-helper cells which help the activation of B-cells.
• The whole antigen binds to the BCR (B-cell receptor), which does not need an MHC complex.
• In the spleen, naive B-, and T-cells enter through the blood and go to their assigned zones.
• Dendritic cells can go to the T-cell/B-cell zones and activate them before they leave through the bloodstream, leading to B-cell activation.
• In the lymph node, naive B-cells, which are unactivated, are present in the primary follicles.
• In the innate immune system, the initiation starts at the site of infection, whereas the adaptive immune system starts in specialized organs like lymph nodes.
• The innate immune system will not have a stronger reaction at the 2nd encounter and the adaptive immune system goes by memory, so it will recognize the same pathogen on the 2nd encounter.
• Innate immune system: phagocytes, granulocytes, and NK cells.
• Physical and chemical barriers in the skin, respiratory tract, and gut prevent bacteria from entering.
• Lysozyme and defensins are antimicrobial proteins that damage and kill bacteria.
• In humans, MHC is called HLA (human leukocyte antigen) and is important for organ transplantation as the HLA should match as much as possible.
• C3 convertase can cleave C3 into C3a and C3b which can trigger either inflammation, phagocytosis, or membrane attack, so a pore is formed and the bacteria will lyse.
• The thymus is where the T-cells mature (positive and negative selection: MHC and ignorance of self-antigens).
• Adaptive immune system: T-cells and B-cells.
• T-cells have a T-cell receptor (TCR) which bind to the peptide (antigen) bound to an MHC complex.
• Lymphoid organs: primary- and secondary lymphoid organs.
• Secondary lymphoid organs filter antigens and activate lymphocytes, T- and B-cells (spleen, MALT, lymph nodes).
• The spleen removes old and damaged red blood cells and filters antigen from the blood.
• The bone marrow is where all the blood cells develop and where the B-cells mature (negative selection: ignorance of self-antigens).
• The complement system consists of 4 different pathways: classical, alternative, lectin, and terminal pathway.
• B-cells have a B-cell receptor (BCR) which can recognize the whole antigen.
• The MALT filters antigen directly from the mucosal epithelium.
• MHC is a part of a protein which in a way can present all (self) proteins of the cell to the immune system.
• The lymph nodes filter antigens from the lymph and tissues.
• Major histocompatibility complex (MHC) is present on all cells with a nucleus and all antigen-presenting cells.
• Primary lymphoid organs are responsible for the development of immune cells (bone marrow and thymus).
• Recognition: non-self (antigens) and pathogen/danger (patterns).
• Lysosomes contain proteolytic- and hydrolytic enzymes, and antimicrobial proteins.