Opsonization and Phagocytosis Flashcards
What is opsonization?
the process of attaching opsonins, such as IgG or complement fragments, to microbial surfaces to target the microbes for phagocytosis
What are opsonins?
Macromolecules attached to the surface of a microbe that can be recognized by receptors on neutrophils and macrophages
What are the primary opsonins?
IgG
Complement factor C3
True or False: Most microorganisms do not need opsonins in order to be phagocytosed.
False, Most microorganisms will NOT be phagocytosed without opsonins present.
Opsonins change the organism’s surface from _________ (relative to the PMN) to more _______.
Hydrophilic –> Hydrophobic
____ receptors on a phagocyte will bind to IgG during opsonization of a microbe.
Fc
How does IgG work to mediate phagocytosis of a microbe?
- IgG attaches to Microbe
- Fc on a phagocytic cell binds to IgG-tagged microbe
- Fc receptor signal activates phagocyte
- Phagocytosis of microbe
How do complement fragments mediate phagocytosis of a microbe?
- C3b (or C4b) bind to the microbe
- Phagocyte C3b-Receptor recognizes bound C3b
- Phagocytosis of microbe
What are the complement by products of neutrophil activation (inflammation/tissue injury)?
C5a and C3a
What are the three common receptors for opsonins?
Fc Lambda (on phagocytes) CR leukocyte integrin Mac-1
When talking about IgG receptors, what are the three classes of the Fc domain on neutrophils (Fc lambda-R)?
Fc lambda-R I (CD64)
Fc lambda-R II (CD32)
Fc lambda-R III (CD16)
What does it mean for a neutrophils to “display death sign”?
The loss of CD16 (Fc lambda-RIII) creates a signal for macrophages to phagocytose the neutrophils.
Which Fc-lambda R is most important for phagocytosis of IgG coated particles and microorganisms?
RII (CD32)
Activation of complement cascade causes _______cleavage of complement factors, creating potential ligands for complement receptors on neutrophil surfaces.
Proteolytic
____ and ____ are chemotactic factors within the complement system.
C3a and C5a
____ and ____ are the main complement derived opsonins.
C3b and C3bi
Name the receptors for fragments of C3.
Type 1: CR1 –phagocytosis, clears immune complexes
Type 2: CR2 – coreceptor for B cell activation
Type 3: CR3 – phagocytosis, leukocyte adhesion
Type 4: CR4 – phagocytosis
What is the major phagocytic cell in the innate immune response that is continually circulating?
Neutrophils
What part of the neutrophil is responsible for killing microbes?
Primary Granules
Secondary Granules
The neutrophil expresses receptors for many bacterial constituents. What are the seven receptors mentioned?
LPS Receptor CR4 Glycan Receptor Mannose Receptor CR3 Scavenger Receptor TLRs
What is the function of macrophages?
Phagocytosis and cytokine production
What is the differences between monocytes and macrophages?
- Monocytes CIRCULATE in the blood
- monocytes differentiate into Macrophages once they enter tissues
What are the common receptors for macrophages?
LPS receptor-CD14 TLR Fc receptors mannose receptors Chemokine receptors IFN
What factors will increase the number of PMNs?
Stress
Injury
Infection
increased cytokines
What are the two primary mechanisms of destruction and killing?
- Oxidative Mechanisms (Reactive Oxygen Species)
2. Non-Oxidative Mechanisms
How would PMN utilize non-oxidative mechanisms for killing and destruction?
Enzymes
Cytoplasmic Granules
pH changes
What are the 5 kinds of phagocytic cells?
- Neutrophils (PMNs)
- Macrophage/monocytes
- Eosinophils
- Basophils
- Dendritic Cells
What are the three mentioned tactics used by pathogens to avoid killing by phagocytes?
- Cytotoxicity (kill or be killed)
- Inhibit opsonization or inactivate phagocytosis
- Survive intracellular killing
