The Lectin Pathway Originates with Host Proteins Binding Microbial Surfaces Lectin: proteins that bind to a carbohydrate MBL (mannose-binding lectin):
The Lectin Pathway Originates with Host Proteins Binding Microbial Surfaces
Lectin: proteins that bind to a carbohydrate
MBL (mannose-binding lectin):
- a protein which binds to mannose residues on glycoproteins or carbohydrates on the surface of microorganisms (structurally similar to C1q)
MASP-1 & MASP-II: MBL-associated serine protease
(structurally similar to C1r and C1s)
Q2: Why doesn’t mannose-binding lectin (MBL) Microbial Surfaces
bind to host carbohydrates?
A2: Mammalian cells normally have sialic
acid residues covering the sugar groups
recognized by MBL and are not a target
Biological Effects Mediated by Complement Microbial Surfaces
1. Cell lysis
The membrane-attack complex can lyse a broad spectrum of cells:
nucleated cells (tumor cells)
Because the activation of alternative and lectin pathways is Ab-independent, these pathways serve as important innate
immune defenses against infectious microorganisms.
2. Inflammatory response Microbial Surfaces
- Various peptides generated during activation of
complement play a role in the development
of an effective inflammatory response.
- C3a, C4a, C5a (called anaphylatoxin) bind to
complement receptors on mast cells and basophils
and induce degranulation with release of histamine
and other mediators.
- The anaphylatoxins also increased vascular permeability,
extravasation, and chemoattraction (induced by
C5a, C3a, and C5b67)
3. Opsonization Microbial Surfaces
- C3b is the major opsonin of the complement system, although C4b also have opsonizing activity.
binds to the surface of microbes
Opsonization by Ab and complement Microbial Surfaces
4. Viral neutralization Microbial Surfaces
- Formation of larger viral aggregates reduces the
net number of infectious viral particles.
- The deposits of Ab and complement on viral
particle neutralizes viral infectivity by blocking
attachment to susceptible host cells and facilitates binding of the viral particle.
5. Clearance of Microbial Surfaces
Inflammation: Microbial Surfaces
Inflammation is non specific response to tissue damage resulting from a variety causes, including heat, chemicals, ultraviolet light, cuts and pathogens.
Acute inflammation is an important part of the second line of defense because it results in:
Components of Innate of defense because it results in:Immunity Inflammation
Heat Redness Swelling Pain Loss of function
Phagocytosis of defense because it results in: –
When WBC's arrive at the site of tissue injury or microbial invasion they become very active and begin engulfing bacteria (or other foreign) that have been opsonized by complement or antibodies; through various mechanisms, bacteria and other foreign substances are destroyed and degraded after phagocytosis
Increase permeability during inflammation of defense because it results in:
Emigration of Neutrophils of defense because it results in:
Chronic Inflammation of defense because it results in:
SinusInflammation Outcome - Resolution
Fever: of defense because it results in:
is a body temperature more than 37 ºC.
- Fever results due the presence of chemicals called pyrogens.
- Pyrogens trigger the hypothalamic thermostat to reset at hightemperature.
Pyrogens include of defense because it results in::
- bacterial toxins
- cytoplasmic contents of bacteria that are released upon lysis Ab-Ag complexes.
- interleukin-1 a pyrogen released by phagocytes that have phogocytized bacteria
Steps of fever of defense because it results in:
Determinants of innate immunity of defense because it results in:
Innate immunity is genetically controlled and varies widely with species, race and to less extent between individuals.
B) Individual differences: of defense because it results in:
Age:the very young and aged are particular liable to infection.
Nutrition: Malnutrition and starvation predispose to infection by decreasing the total white cell count and phagocytosis.
Hormones: Some endocrine diseases cause a decrease in resistance to infection such as diabetes mellitus, hypothroidism and adrenal dysfunction.