humoral immune response

What are immunoglobulins (Igs) or antibodies (Abs)?

Glycoproteins present in the gamma-globulin fraction of the serum

What cells produce immunoglobulins?

B cells or plasma cells

What does the basic unit (monomer) of an Ig molecule consist of?

2 identical heavy (H) & 2 identical light (L) chains

How are the heavy and light chains linked?

Covalently by disulfide bonds

Each heavy (H) and light (L) chain has what two regions?

A variable (V) and a constant (C) region

The hypervariable regions at the tip of each arm are also known as…?

Complementarity-determining regions (CDRs)

What part of the antibody do antigens bind to?

The Fab region (antigen-binding sites)

What part of the antibody determines its effector function?

The Fc region

How are the 5 immunoglobulin isotypes (classes) determined?

By changes in the amino acid sequence of the constant region of the heavy chain

What are the 5 isotypes of heavy chains?

IgG (γ), IgM (μ), IgE (ε), IgA (α), IgD (δ)

The process where T cells stimulate B cells to produce different heavy chain isotypes is called…?

Heavy chain Isotype (Class Switching)

Which cytokine, produced by T helper cells, stimulates switching to IgE?

IL-4

Which cytokine stimulates switching to IgA, especially in mucosal tissues?

IL-5 and TGF-β

What is the most important Ig in secondary immune responses?

IgG

Which IgG subclasses cross the placenta to protect the fetus?

IgG1, 3, and 4

What is the structure of IgM?

A pentamer (5 monomeric units linked by a J chain)

What is the predominant antibody in the primary immune response?

IgM

An elevated IgM level in a newborn's cord serum indicates…?

Fetal infection before birth (intrauterine infection)

What is the predominant immunoglobulin class in external secretions (milk, saliva, tears)?

IgA

What is the structure of secretory IgA?

A dimer (two IgA monomers, a J chain, and a secretory piece)

What is the function of the "secretory piece" on secretory IgA?

Facilitates transport across mucosa and protects it from digestion

What is the main function of secretory IgA?

To provide local immunity at mucous surfaces by preventing adherence

Which Ig is found in very low levels in serum and acts as an Ag receptor on B cells?

IgD

Which Ig binds to Fc receptors on eosinophils, basophils, and mast cells?

IgE

The cross-linkage of receptor-bound IgE by an antigen (allergen) causes…?

Degranulation (release of histamine, etc.) leading to allergic manifestations

What is the first phase of the primary immune response (1-2 weeks)?

Latent or lag period

What is the first class of antibody detected in the primary immune response?

IgM

Which immune response is characterized by a short latent period and high concentrations of IgG?

Secondary Immune Response

What cells are responsible for the rapid secondary immune response?

Memory B and T cells

What is the antibody-mediated function that blocks the functional domain of toxins or viruses?

Neutralization

What is the process where antibodies coat microbes to make them more easily ingested by phagocytes?

Opsonization

Which antibody is a potent opsonin?

IgG

Which antibody is the most potent complement activator?

IgG3 (and IgM)

Which antibody-mediated function involves effector cells (like NK cells) lysing a target cell bound by antibodies?

Antibody-dependent Cellular Cytotoxicity (ADCC)

NK cells, neutrophils, macrophages, and eosinophils mediate ADCC because they have…?

Receptors for the constant region of IgG (Fcγ)

What are monoclonal antibodies?

Highly specific antibodies produced against a single epitope by immortal cells

How are monoclonal antibodies (mAbs) produced?

By fusing a myeloma cell with a specific B cell

What is the resulting fused cell called?

A hybridoma

What are the two key properties of a hybridoma cell?

It produces a single type of Ab (specificity) and continually divides (immortality)

What are some laboratory uses for monoclonal antibodies?

HLA typing, hormone assays, identifying microbes/cancer cells

What is the complement system?

A series of at least 25 plasma proteins involved in host defense and inflammation

What are the three pathways of complement activation?

Classical, Alternative, and Lectin

Which complement pathway is initiated by an antigen-antibody complex (IgM or IgG)?

Classical pathway

Which complement pathway is initiated by microbial surfaces (e.g., endotoxin) and does not need antibodies?

Alternative pathway

Which complement pathway is initiated by Mannose-Binding Lectin (MBL) binding to microbial surfaces?

Lectin pathway

What is the central amplification step in all complement pathways?

The splitting of C3 into C3a and C3b

What is the final product of the complement cascade that forms holes in cell membranes?

Membrane attack complex (C5b6789)

Which complement component is a major opsonin?

C3b

Which complement components are anaphylatoxins (cause mast cell degranulation)?

C5a, C3a, C4a

Which complement component is a potent chemotactic factor (attracts phagocytes)?

C5a

Deficiency in terminal components (C5-C9) makes individuals highly susceptible to…?

Neisseria infections

Deficiency in early components (C1, C2, C4) is associated with a higher risk of…?

Autoimmune diseases like SLE