adaptive immune system Flashcards
Adaptive immune system basics
- can distinguish between two antigens by a single amino acid . . the adaptve system can be sub-divided into two humoral immunity and cell-mediated immunity . cells of AIS = lymphocytes (B-cells, + T-cells )
B lymphocytes(generated in bone marrow )
produce antibodies and are responsible for humoral immunity, recogises antigens via antibodies that are hound to b-cells also called b-cell receptors.
t-lymphcytes (generated in thymus )
Responsible for cell mediated immunity and recognise antigens via a t-cell receptor (TCR)
primary and secondary organs of immune system
primary organs
- bone marrow and thymus (supplies lymphoid organs with mature cells)
Secondary organs
- lymph nodes, adenoids, tonsil, spleen, peyers patches
Bone marrow
site of haematopoietic cell division and production of all blood cells. b-cells differentiate in the bone marrow and directly enter the blood stream. t-cells are produced and then move to the thymus to mature before entering the blood stream. b cell function decrease with age and t cell
Thymus
Site of t-cell development, maturation and selection. upto 95% of thymocytes will not leave the thymus as they undergo apoptosis only if they recognise a non-self antigen on MHC then they can leave thymus. function decreases with age,
Lymphatic system
The LS drains extracellular fluid from all around the body and returns it to the blood in the thoracic duct. A response between an antigen and lymphocyte in the lymph node often results in marked swelling
secondary lymphoid tissue
spleen
- filters blood borne antigen removes old red blood cells
Mucosal associated lymphoid tissue(MALT)
- collection of lymphoid tissue in respiratory and UrinaryT’s,
peyers patches
- collections of lymphoid tissues in appendix and small intestine
tonsils
- small organs in the pharynx that are filled with macrophages
B-lymphocytes and antibodies as receptors mechanism of acton
a b-lymphocyte produces one specific antibody which is presented on the b-cells surface, when an antigen binds to the b-lymphocyte via antibody(receptor) then a large number of plasma cells are produced all of which produce antibodies . the soluble antibody can bind to microbes and activate the complement cascade this is the third pathway of complement activation(classic pathway)
b-lymphcytes and MHC 2
the b-cells endocytosis (not phagocytose) bound antigens and then is processed and presented to t-cells via the MHC 2 . this results in the secretion of cytokines and promotes proliferation and activation of b-cells and other cells of the immune system.
T cell activation
Step 1: antigen recognition (binding of a matching MHC-peptide to the TCR. Step 2: so-stimulation =. dendritic cells provide co-stimulation for the naive t cell to undergo clonal expansion. DETAILS on slide
what t-cells are formed from interaction between CD4 and CD8 proteins
In addition to a t-cell receptor, most t cells also express either CD4 or CD8 protein on the outer surface of their membrane. both CD4 and CD8 are attached to an intracellular protein tyrosine kinase and if activated a signal transduction cascade is initiated. CD8+ t-cells interact with MHC class 1 molecules and typically differentiate into cytotoxic t-cells. CD4+ t-cells interact with MHC class 2 molecules differentiate into helper t-cells.
Th1 cells
primarily involved in coordinating responses to intracellular pathogens and involves activating macrophages and cytotoxic t-cells. the cytokines they secrete include
- interferon-y and TNF-a and they activate macrophages.
- IL-2 promotes proliferation of cytotoxic t-cells.
- IL-3 and GM-CSF lead to growth and differentiation of neutrophils and macrophages.
-Interferon-y inhibits proliferation of TH2 cells.
Th2 cells
il-4 - promotes igE production (facilitating eradication of parasites)
IL-5 - promotes eosinophilia (“)
Il-6 - differentiation of B cells to plasma cells
IL- 13 - activates b cell proliferation and promotes IgE production
IL-4 inhibits proliferation of th1 cells
Th17 cells
- prominent in autoimmune reactions. provides inflammatory response towards extracellular bacterial and fungal infections .
-produces IL-17A, IL-17F AND IL-22 which they trigger endothelial and epithelial cells to produce proinflammatory cytokines that promote neutrophil recruitment and secretion of antimicrobial peptides.
