L12 The Complement System Flashcards
What are the 3 ways to activate the complement system and how are they activated
Classical pathway:activated by antigen antibody complex and thus triggered after generation of specific antibody to a particular Ag(igG and igM)
Alternative pathway: can be activated by microbial cell surface substances
Bacterial poly and liposaccharides of cells envelop of gram negative bacteria both serve as potent initiating stimuli
Lectin binding or mannose binding pathway: activated when mannose binding lectin binds to carbohydrates on the pathogen
Which pathways are considered part of innate immunity
Alternative and lectin
What does activation of complement components involve
cleavage of complement proteins(c3)(c5)leading to generation of effector mol(C-3a+C-3b) that participate in eliminating microbes in diff ways
What happens to activated complement proteins
Become covalently attached to the microbial cell surfaces where activation of complement components occurs
What is formed from complement pathways and what does it do
Complex enzyme C3 convertase and its capable of binding and cleaving a key protein C3 common to all 3 pathways
How do all pathways proceed after C3 activation
Binding of late acting components to form a membrane attack complex which is C5b,6,7,8,9 which becomes inserted in the lipid bilayers of foreign membranes ultimately causing cell lysis
What are biologic functions of the complement system
1-cell lysis:insertion of MAC in to cell membrane leads to lysis of many types of cells
2-opsonization of pathogens: microbes such as bacteria and viruses are phagocytized much more efficiently in presence of C3b bound on their surfaces because of presence of C3b receptors of many phagocytes
3-inflammatory function:
Chemotaxis and anaphylatoxins
4-enhancement of antibody production: binding of C3b derivatives to its receptor on the surface of b lymphocytes enhances antibody production
What is chemotaxis
C5a attracts phagocytic cells mainly polymorphs to site of inflammation and inc their activity
What is anaphylatoxins
C3a and c4a and c5a can produce degranulation of mast cells with release of mediators which cause capillary dilatation
What is the major histocompatibility complex
Collection of highly polymorphic genes on the short arm of the chromosome 6 in the human
2 major classes of cell bound MHC gene products: 1 and 2
Can also be called human leukocytic antigens (HLA)
Describe class 1 of MHC antigens
Glycoproteins and include HLAA HLAB AND AND HLAC
Expressed on all nucleated cells in body
Co dominant expression
Enables cytotoxic cells(CD8) to recognize foreign antigen on surface of graft cells, tumor cells or virus infected cells and kill these cells
What is MHC restriction
Cytotoxic cells only work when they recognize both antigen and class 1 MHC molecules in close association on surface of cells
Helper t cells(CD4) will recognize foreign antigen on the surface of APC only if they are associated with class 2 MHC molecules
Describe class 2 MHC antigens
Also known as HLA D antigens
Glycoproteins
Include HLA DP HLA DQ HLA DR
Expressed on antigen presenting cells of body such as macrophages,dendritic cells and b lymphocytes
How can both classes be typed
Flow cytometry
Molecular techniques such as pcr
Importance of MHC
▪️Organ transplantation: depends on compatibility of MHC genes of donor and recipient
▪️MHC restricted antigen presentation: ability of t cells to recognize antigen is dependent on association of antigen with either class 1 or 2
Tc cells recognize 1 and th recognize 2
▪️Disease association:presence of certain HLA antigens is often associated with a particular disease
▪️Paternity testing and forensic investigations
