Comp 2

Complement System

Protective system common to all vertebrates.

Innate Immunity

Immediate response to pathogens without prior exposure.

Adaptive Immunity

Specific response involving antibodies against pathogens.

Serum Glycoproteins

20 proteins in plasma involved in complement.

Cascade Activation

Sequential activation of complement factors.

Coagulation Cascade

Similar activation sequence for blood clotting.

Activation Pathways

Three pathways leading to complement activation.

Classical Pathway

Requires antibodies (Ig) for activation.

Alternative Pathway

Triggered by microorganisms without antibodies.

Lectin Pathway

Does not require antibodies for activation.

C3 Activation

Key step in all complement pathways.

Anaphylatoxin

Substance that induces inflammation and immune response.

Opsonisation

Process of marking pathogens for destruction.

C3a

Anaphylatoxin generated from C3 activation.

C3b

Opsonin that enhances phagocytosis of pathogens.

Membrane Attack Complex (MAC)

Structure that lyses pathogen membranes.

Inactive C3b

Form of C3b when no pathogen is present.

Mannose Binding Lectin (MBL)

Initiates lectin pathway of complement activation.

C3 Convertase

Enzyme complex that cleaves C3 into C3a and C3b.

Complement Nomenclature

Components numbered C1-C9 based on discovery order.

C4b2a

Active protease complex in Classical Pathway.

Classical Pathway

Complement activation requiring antibody binding.

C1 Complex

Consists of 6C1q, 2C1r, 2C1s molecules.

Complement Fixation

Binding of antibody to antigen activates complement.

C1q

Globular molecule binding to Fc portion of Ig.

IgM

Antibody with five Fc fragments for activation.

IgG

Antibody class that can activate complement.

C3 Convertase

Enzyme complex formed by C4b2a.

C4b

Membrane-bound component that binds C2.

C4a

Soluble fragment triggering mast cell degranulation.

C2a

Fragment that remains attached to C4b.

C2b

Soluble fragment that diffuses away.

C3b

Opsonin that binds to antibody surface.

C3a

Anaphylatoxin causing mast cell degranulation.

C5 Convertase

Complex formed by C4b2a3b.

C5a

Diffusible fragment triggering vasodilation and chemotaxis.

C5b

Labile component that binds C6 for activation.

C5b678 Complex

Forms membrane attack complex in cell lysis.

C9

Final component added to membrane attack complex.

Mast Cell Degranulation

Release of histamine triggered by C3a and C5a.

Vasoactive Amines

Substances released affecting blood vessel permeability.

Anaphylatoxin

Substance causing mast cell degranulation and inflammation.

C9 Molecules

Assemble to form 100Å diameter pores.

Membrane Attack Complex (MAC)

C5b678(9)n complex forming pores in membranes.

Pore Function

Allows passage of ions, small molecules, water.

Osmotic Pressure

Increases, causing water influx and cell lysis.

Alternative Pathway

Ig-independent complement activation pathway.

C1, C4, C2

First three components absent in Alternative Pathway.

C3 and C5-C9

Components involved in the Alternative Pathway.

C3 Convertase

C3bBb complex, cleaves C3 for amplification.

Tickover

Continuous low-level breakdown of labile C3.

C3b Inactivation

Regulatory proteins inactivate C3b within seconds.

C3b Opsonin

Enhances phagocytosis by marking pathogens.

Factor B

Binds to C3b, cleaved by factor D.

C3bBb Stabilization

Stabilized by Properdin (P) for activity.

C5 Convertase

C3bPBb3b, equivalent to classical C5 convertase.

C5a and C5b Generation

End of pathway identical to Classical Pathway.

Lectin Pathway

Innate immune pathway, antibody independent.

Mannose Binding Protein (MBP)

Binds mannose on pathogen surfaces.

MASP Proteases

MBP-associated serine proteases cleaving C4 and C2.

C3 Importance

Pivotal in complement activation; deficiency leads to infections.

Complement Deficiencies

Rare in unselected populations, lead to diseases.

C3b Binding

Attaches to microbial surfaces, enhancing opsonization.

Functional Redundancies

Multiple immune system functions may overlap.

Autoimmune Diseases

Conditions where the immune system attacks self-tissues.

C3 Deficiency

Severe disease linked to infections and autoimmune phenomena.

Complement System

Mediates inflammation and immune responses.

Regulatory Mechanisms

Control activation to prevent tissue damage.

Short Half-Lives

Active components lose function quickly post-activation.

Regulatory Proteins

Limit damage to host tissues during activation.

Innate Autoreactivity

Immune response against body's own cells.

Thrombotic Microangiopathy

Characterized by anemia and endothelial damage.

Complement Inhibitors

Prevent excessive inflammation and tissue injury.

Secondary Complement Deficiency

Increased infection risk due to uncontrolled activation.

Kinin System

Involved in inflammation, interacts with complement.

Coagulation System

Blood clotting process that can be affected by complement.

Complement Dysregulation

Leads to diseases triggered by infections or stress.

Therapeutic Complement Inhibitors

Medications to control excessive complement activation.

Opsonisation

Enhances phagocytosis by marking pathogens.

Membrane Attack Complex (MAC)

Forms pores in pathogen membranes for destruction.

Classical Pathway

Activation requiring antibodies IgG or IgM.

Alternate Pathway

Initiated by C3b binding to pathogens.

Mannose Binding Lectin (MBL) Pathway

Binds mannose on pathogens to activate complement.

C3 Convertase

Enzyme that cleaves C3 in complement activation.

C5 Convertase

Enzyme that cleaves C5, leading to MAC formation.

Primary lymphoid organs

Sites for lymphocyte development and maturation.

Bone marrow

Location for hematopoiesis and lymphocyte origin.

Thymus

Site where T cells mature from bone marrow.

Secondary lymphoid organs

Sites for lymphocyte activation and immune response.

Lymph nodes

Filter lymph and facilitate immune cell interactions.

Spleen

Filters blood and activates immune responses.

Diffuse lymphoid tissue

Loose arrangement of lymphoid cells in mucosal areas.

Nodular lymphoid tissue

Organized lymphoid structures, includes solitary and aggregate nodules.

Solitary nodule

Single lymphoid nodule found in various tissues.

Aggregate nodule

Cluster of lymphoid nodules, e.g., Peyer's patches.

Hematopoietic stem cell

Stem cell in bone marrow producing immune cells.

Adaptive immune cells

Lymphocytes committed to specific antigens.

Immunocompetent

Fully developed lymphocytes capable of immune response.

Interstitital fluid removal

Function of lymphatic system to maintain fluid balance.

Fatty acid absorption

Transport of fats as chyle into circulation.