Antigens and Antibodies

Antigens

Bacteria, fungi, protists, viruses contain biochemicals that the body recognizes as foreign and attacks. Lymphocytes bind to these and trigger an adaptive response

Epitopes

3D regions antigens contain that dictate the adaptive immune response.

Large and Complex Foreign Macromolecules

Things like proteins and glycoproteins on the pathogen surface that make the best antigens as they contain many distinct shapes that serve multiple epitopes

Small and Simple Molecules

Poor antigens as they don’t have many epitopes

Exogenous Antigens

Structures on the outside or surface of microbes like cell walls, membranes, flagella, pili, toxins, or extracellular enzymes

Endogenous Antigens

Pathogens that reproduce inside a body’s cells. Our lymphocytes only detect these if our cells incorporate or add them to their plasma membrane

Autoantigens

Molecules that are produced by our own cells. In autoimmune disorders, our immune system believes they are foreign even though they are not

B Lymphocytes

Found mostly in MALTs, lymph nodes, tonsils, and the spleen. Only a small portion are found in the blood stream. Main function is to produce and secrete antibodies and will also detect exogenous antigens on extracellular pathogens

Each one will generate a single BCR that recognizes one epitope

AKA immunoglobins

B Cell Receptor

Has variable regions that make contact and detect the epitope. The variable region contains a different structure/amino acid sequence on each B cell which means each B cell recognizes a different epitope

Plasma Cells

When B cells are activated and secrete one type of antibody

B Cell Antibody Secretion

Antibodies secreted are the same as the BCRs except they don’t have a transmembrane domain as they aren’t attached to a cell membrane. Variable region is exactly the same, and will bind to the same epitope

Neutralization

Antibody function that binds to critical part of toxin preventing it from damaging the cell. Also bind to adhesion proteins found on the surface of pathogens so they can’t bind to host cells

Opsonization

Antibody function that stimulates and aids in phagocytosis, these act like handles that allow phagocytes to grab on to

Oxidation

Antibody function that damages pathogens and can completely eliminate them. These steal elections from biochemicals and cell structures in the pathogen. The damage done cannot be repaired and can lead to the death of the pathogen

Agglutinatioin

Antibody function. Each antibody has two binding sites and bind two pathogens at once. This increases the chance the pathogens get phagocytized or filtered out of the blood by the spleen

Antibody Dependent Cellular Cytotoxicity (ADCC)

Natural killer lymphocytes bind to antibodies on a viral infect cell. They then create a hole in the cell membrane and release an enzyme that triggers cell death

IgM

The first antibody produced in an adaptive immune response. Can trigger inflammation and can agglutinate or neutralize a pathogen or enzymes/toxins it produces

Class Switching

The plasma cell after producing IgM antibodies can switch to produce IgG, IgA, IgE, or IgD

IgG

The antibody that is most common, longest lasting antibody, and has the most functions. Can trigger ADCC, neutralize, and opsonize a pathogen. Moves through the blood the easiest and fastest, binds to pathogens trying to enter the circulatory system, blocking their access to blood.

Has the longest half life in the blood

IgA

Circulates in our blood and can agglutinate or neutralize pathogens.

Secretory IgA

Plasma cells add a secretory component that protects it from intestinal enzymes. These are made by cells in the lacrimal apparatus, mucus membrane, and mammary glands. Newborns can receive this from mothers if they are breast fed

IgE

involved in response to parasites and allergens, trigger mast cells and basophils to release inflammatory chemicals like histamine

IgD

Found on the surface of B lymphocytes early in the adaptive immune response, not quite sure what their exact function is yet

T Lymphocytes

Act against intracellular pathogens (endogenous antigens) and body cells that produce abnormal antigens (cancer cells). Will mature in the Thymus and circulate in lymph/blood vessels to lymph nodes, spleen, tonsils, and MALTs

T cell Maturation

Incorporating T cell receptors into the plasma membrane. There are at least 1 billion different types of TCR and each cell expresses one type of T cell receptor and will bind to one epitope. If they react against autoantigens that are eliminated by apoptosis

Cytotoxic T Lymphocyte

Directly kills viral infected cells or cancer cells by injecting it with enzymes that induce cell death

Perforin

A protein secreted by Cytotoxic T Lymphocytes that create a pore in the cell membrane of the pathogen

Granzyme

An enzyme that is released after perforin by Cytotoxic T Lymphocytes that triggers apoptosis

Helper T Lymphocyte

Help regulate the activity of B cells and cytotoxic T cells by providing growth factors and chemical signals. Secrete various soluble protein messengers called cytokines that regulate the entire immune system, both adaptive and innate portions

Type 1 Helper T Cells

Will assist cytotoxic T cells that regulate innate immunity

Type 2 Helper T Cells

Function in conjunction with B cells. Will secrete a cytokine called Interleukin 4

Interleukin 4

Secreted by Type 2 helper T cells that causes an inactive B cell to turn into an active plasma cell

Regulatory T Lymphocytes

Slow down and completely turn off the adaptive immune system by secreting cytokines that suppress the adaptive immune response and promote tolerance of certain antigens.

Can inhibit activity, promote their lysis, and tell them to stop dividing

Memory T Cells

Persist for months or years in lymphoid tissues and are immediately functional upon subsequent contacts with epitopes. These are more effective than the initial primary response