Imm - Antibodies + some responses

What does the IgM antibody isotype do?structure?

First response, circulates in blood, pentamer (massive), strongly activates complement

(M = Massive & Meets first)

What does the IgG antibody isotype do? structure?

Blood + tissues, crosses placenta, neutralizes + opsonizes, monomer

G = Goes everywhere

What does the IgA antibody isotype do? structure?

Mucosal secretions → protects body entrances/surfaces through barrier neutralization, secreted dimer

(A = At the entrances)

What does the IgE antibody isotype do? structure?

Bound to mast cells → allergies + parasite defense → mast-cell activation; monomer

(E = Emergency allergy)

What is affinity?

strength of one binding site for one epitope

what increases affinity?

selection of higher-affinity B-cell clones

What is avidity?

Total strength of all stimultaneous interactions

What increases avidity?

multivalency and favorable geometry

What is neutralization?

The blocking os attachment, entry, or toxin action

What increases neutralization?

Fab binding to a critical site

(Fragment antigen-binding - It is the part of an antibody that actually binds to the antigen/epitope.)

• ____ region → Finds and binds the antigen

• ____ region → Calls/recruits immune functions after the antigen is bound

• Fab

• Fc

Fab = Finds Antigen & Binds

Fc = Calls for help

What is opsinization?

Coating a target for phagocyte recognition

What increases opsinization?

Fc receptor binding; C3b can also opsonize

Affinity is often confused with?

Number of binding sites

Affinity is the strength of binding between ONE antibody binding site and ONE epitope. It does not describe how many binding sites an antibody has. Higher affinity means that each individual binding site binds its epitope more strongly.

Avidity is often confused with?

Single-site affinity

Avidity is the total combined strength of ALL simultaneous antibody-antigen interactions. Affinity measures the strength of only ONE binding site–epitope interaction. Therefore, an antibody can have moderate individual affinity but high overall avidity if it makes many simultaneous interactions.

Netralization is often confused with?

FC-mediated killing

Neutralization occurs when the antibody's Fab region binds a critical site on a pathogen or toxin and blocks attachment, entry, or toxin activity. It does not require the Fc region to recruit another immune cell to kill the target.
Neutralization = block the threat, whereas Fc-mediated killing = recruit immune mechanisms to destroy the target

Opsonization is often confused with?

Direct membrane lysis

Opsonization means coating/tagging a target to make it easier for phagocytes to recognize and engulf. Antibody Fc regions and complement C3b can act as opsonins. It does not directly rupture the pathogen's membrane.
Opsonization = tag it for phagocytosis, whereas lysis = directly break the membrane and kill it.