MLT 115 Mod 2 Les 2: Complements

General Guidance for Students

  • Important advice: Check your email on Sunday night before going to bed, especially if you have classes on Tuesday or Thursday, to stay updated on potential changes or announcements.

Overview of Immune System Function

  • Functions of the immune system:

    • Identify foreign materials.

    • Defend against foreign invaders.

  • Importance of recognizing self-cells in the immune response.

Autoimmune Responses

  • When the immune system mistakenly identifies self-cells as foreign = Autoimmune response.

Lines of Defense Against Infection

  • First line of defense:

    • Unbroken skin (IgE's role is not critical until the barrier is breached).

  • Activation of cellular response after skin is compromised.

    • Neutrophils are usually the first cells to respond to an injury.

    • Neutrophils perform phagocytosis.

Immune Response Overview

  • Pathway for an activated immune response:

    1. Injury occurs.

    2. Neutrophils are activated.

    3. Introduction of the antigen to lymphocytes (T-cells or B-cells).

    4. B-cells differentiate into plasma cells and produce antibodies.

Antibodies and Immunoglobulins

  • Types of antibodies and their characteristics:

    • First antibody produced: IgM.

    • Structure: Pentamer (five Y-shaped subunits, each with two heavy chains = total of 10 antigens).

    • Second antibody produced: IgG.

    • Predominant in secondary immune response (anamnestic response).

    • IgM cannot cross the placenta.

    • Due to its large size.

    • Passive immunity:

    • Via mother to baby through colostrum or across the placenta.

    • Natural active immunity:

    • When a child acquires disease from an infected sibling.

    • Vaccination is a method of gaining acquired immunity.

Hypersensitivity Reactions

  • Most dramatic hypersensitivity response: Anaphylaxis.

  • Key immunoglobulin involved in allergic responses: IgE.

Antibody Composition

  • Antibodies are composed of proteins.

  • Stuctures include light chains (Kappa and Lambda) and heavy chains (H and L chains).

  • Antigenic determinant: Epitope, the specific region of an antigen recognized by an antibody.

Infection Control Practices

  • Standard precautions to reduce infection:

    • Handwashing.

    • Treat all materials as potentially infectious.

Clinical Laboratory Standards

  • Federal regulations for laboratories: Clinical Laboratory Improvement Act of 1988 (CLIA).

Antibody Binding Sites

  • Binding sites for antigens: FAB (antigen-binding fragment) and bind at the C-terminal region.

  • FC (fragment crystallizable) region is responsible for complement activation.

  • Types of immunoglobulins and their prevalence:

    • IgA predominant in mucosal secretions.

    • IgG is less than 1% of total immunoglobulin in some conditions.

Immune Response Dynamics

  • Primary immune response characterized by a lag before IgM appears.

  • Secondary immune response characterized by faster IgG production.

  • Melting curve dynamics of antibody production: leg phase, log phase, plateau and decline.

Safety and Laboratory Practices

  • Understanding of safety protocols and knowledge of safety manuals is crucial for laboratory environments.

The Complement Immunity

  • The complement Immunity are things that enhances the immune response and is critical in inflammation.

  • The complements are also known as mediators and helpers

  • Compliment activation happens when an antigen-antibody bond exists

  • Anaphylatoxins break off and builds up, leading to anaphylactic shock in an allergic reaction. Activation of complement components from C3 onward leads to generation of anaphylatoxins

  • Complement pathways (there are 3 of them):

    • Classic pathway: slower, requires antigen-antibody binding.

    • Alternative pathway: quicker and responds to certain pathogens without prior antibody involvement.

    • Lectin Pathway- We don’t worry about this one.

Classic Pathway

  • This pathway is activated when an antigen-antibody complex is formed

  • IgM and IgG complexes both work to activate complement, but IgM complexes work best

  • There are 9 components of complement, C1-C9

  • Here are the few things we will focus on:

-C1q, C1r, &C1s = the recognition units

  • This complement is activated when an antigen-antibody complex is present and it initiates the pathway

-The Classic Complement pathway is at its full amplitude when C3 is activated (like a runway train).

-C5bC6C7C8C9 = the membrane attack complex (The Terminator complement)

  • This complex will insert itself into the infected cell and destroy the cell and the offending antigen.

-C3 is the complement component with the highest concentration circulating around the body.

-The most common complement deficiency that effects people is C2

  • Deficiency of this complement causes people to suffer with repeated bacterial infections and autoimmune disorders

  • This pathway takes the longest out of the 3 and involves virus, fungus, and tumor lysis

  • The 3 Stages of the Classic Pathway’s Antigen-Antibody bond:

    1. Recognition of the antigen-antibody bond complex by C1.

    2. Amplification of the cascade, where the complex builds momentum like a snowball gaining size and speed.

    3. Formation of the Membrane Attack Complex (MAC), which leads to cell lysis.

  • Components in classical pathway:

    • C1q, C1r, & C1s = Recognition Unit; responsible for binding to the antibody's FC region.

    • C3b = Amplification of cascade

    • C3= full amplitude, highest concentration in the blood, No turning back

    • C5bC6C7C8C9 = Membrane Attack Complex- Destroys the cell (cell lysis)

    • C8 = Bound to C5bC6C7 causes the cell to be permeable

Alternative Pathway

  • It is also called Properidin pathway

  • It bypasses the first 3 steps of the Classic Pathway

  • It bypasses the activation of C1, C4 and C2

  • Bacterial endotoxin is present here

What happens in the Alternative Pathway

  • This pathway requires a bacteria that produces endotoxin

  • It skips the activation of C1, C4, and C2

  • Factor B activates C3 to form the C3bBb complex (Factor B can also be called “Begin” bacteria)

  • C3bBb acts on C5 to intiate the formation of the Membrane Attack Complex (C5b6789 for short)

  • It can be activated by bacterial endotoxins without IgM or IgG

  • The Pathway can be stopped or controlled by Factor H (Factor H for “Halt”). This happens by preventing Factor B from binding with C3b

  • It’s a very effective pathway

Regardless of the Pathway, what happens when complements are activated (The side effects)?

  • Blood Vessels Dilate

  • Increased Memebrane Permeability- This happens when the complement is activated for Ion exchange. This also increases the membrane fragility, which happens when blood vessels dilate.

  • Decreases blood pressure when membrane permeability increases

  • Activates coagulation; causing thrombosis, leading to tissue death

  • Starts Shock (“She’s going into shock”)

  • Disseminated Intravascular Coagulation (DIC)- Small intravascular clots that cause the depletion of coagulation factors and platelets. This causes uncontrollable bleeding and it can be devastating and often fatal.

  • Fluid Loss

  • Hypovolemia- a state of decreased blood (fluid) volume, which results in inadequate circulation and can exacerbate the effects of shock.

  • Opsonization- the process where pathogens are identified and destroyed.

-The cells are coated with antibodies

-The cells that are coated with antibodies are destroyed by the spleen and phagocytized by macrophages (reticuloendothelial system.)

What Happens to People with Decreased Complement Levels?

  • People can more easily develop bacterial infections, especially streptococcal and Neisseria sps.

  • They are at risk of hemolytic syndrome

  • They may have increased respiratory infections in infancy an early childhood

  • They may develop autoimmune disorders as young and middle-aged adults

Inflammatory Conditions and Complement Activation

  • Conditions leading to elevated complement levels include:

    • Severe trauma, inflammatory conditions, COVID-19, various bacterial infections such as E. coli O157, among others.

  • C3 and C4 are the acute phase reactants that increase during inflammation but are not diagnostic for specific diseases.

Review of Essential Topics

  • Key topics for exams include immune response pathways, antibody characteristics, clinical lab regulations, and safety practices in lab environments.