MBIO 1010 / Topic 5c: Humoral Immunity

What are antibodies (Ab) also called?

Immunoglobulins (Ig).

Specifically, what specific molecule is an Ig? What is this specific molecule composed of?

Glycoproteins composed of four subunits.

Give me the full anatomy of an Ig.

The four subunits are made of two identical heavy chains and two identical light chains. Each Ig has two identical antigen binding sites (F_ab) and site for interaction with other components of the immune system (F_c)

What are the five classes of antibodies? Give each its”-merness,” i.e. if it’s a monomer, dimer, etc.

• IgG, a monomer.

• IgM, a pentamer.

• IgA, a dimer.

• IgD, a monomer.

• IgE, a monomer.

What are two characters of IgG?

• Mostly abundant in blood and tissues.

• Most important for combating a pathogen.

What are three characters of IgM?

• First antibody made when a new antigen is encountered.

• Excellent at agglutination, which is sticking multiple things together.

• Does not leave blood and enter tissues.

What is the one character of IgA?

Secreted into saliva, tears, and mucosal tracts, acting as defence against any infections in mucosal tracts.

What is one character of IgD?

B cells have surface IgD that finds the antigen they can make Ab against. When activated against antigen, they can make other classes of Ab.

What is one character of IgE?

Coats surface of basophils and mast cells which helps them recognize specific unique intruders. Multiple antigens bridge across IgE, causing mast cells to degranulate.

What are the five protective functions of Ab?

• Neutralization.

• Opsonization.

• Agglutination..

• Antibody mediated cytotoxicity.

• Complement activation.

What happens in neutralization? What Ig works best for neutealization?

Ab on host cells stick to epitomes, blocking receptors so that pathogens don’t enter host cells. IgG works best.

What happens in opsonization?

Ab sticks to pathogen’s surface and flags down phagocytes. Once phagocytes arrive, the phagocytes attach to the Ab by attaching to F_c, engulfing antigen thereafter.

Opsonization greatly ________ the rate of __________.

Opsonization greatly increases the rate of phagocytosis.

What happens in agglutination?

Ab rallies up antigens for ease of phagocytosis.

What happens in antibody mediated cytotoxicity?

F_ab binds to antigen on surface of parasite, and F_c binds to eosinophils. What this essentially does is mount a machine gun of enzymes and oxygen intermediates on the parasite’s headquarters to attack the parasites.

What happens in complement activation?

Once F_ab binds to a bacterial cell, it can activate a complement.

What is a complement? What did the Ab pretty much do?

A protein cascade made of around 30 proteins in blood assisting other components of immune system. The Ab pretty much told a soldier (protein) to call another soldier and repeat to kill the rebels (pathogens).

True or false: Complement is involved in both response systems of the immune system.

True.

What are the three major functions of the complement cascade?

• Membrane attack complex (MAC).

• Opsonization.

• Enhanced inflammation.

What happens in the MAC?

Complement proteins poke holes only in Gram negatives.

With Gram positives, MAC won’t work. Why?

Thick peptidoglycan, cannot be poked.