Antibodies

IgG

This is by far the most common antibody that circulates in the blood. *babies receive all the mom's various IgG in breast milk, providing immunity to whatever the mom is immune to. *for good and for bad, these antibodies can cross the placenta and protect (or harm, as in the case of antibodies made to the Rh antigens on a baby's blood cells) *If someone has a "titre" for a disease (measles, for example), the blood sample is measuring the individual's IgG levels.

IgD

This is the most mysterious antibody! It appears to play roles in the initial response, being produced along with IgM. But it also appears to be able to bind and stimulate mast cells and basophils (like IgE). It's very uncommon in the blood, and usually remains bound to a circulating and activated B cell.

constant region of an antibody

Unlike the variable region, the constant region doesn't bind the recognized antigen. It is responsible for activating, for example, complement, or other white blood cells. It also can be important for anchoring an antibody to a cell type such as a mast cell or basophil. It is specialized for binding to or activating whatever it needs to in that environment. It is specialized for that "body habitat"

cross-reactivity of antibodies

When an antibody to an antigen on a pathogen can also bind to an antigen on part of the host. Rheumatic fever is a classic example, in which antibodies to Streptococcus pyogenes bind to the heart valves, the joints, and the kidneys.

plasma cell

a fully activated and developed B cell lymphocyte that produces a single type of antibody.

immunoglobulin

an antibody

hypersensitivity

an exaggerated response by the immune system to a particular antigen. If the antigen is in the environment (food or pollen, for example), this is called an allergy. If the antigen is part of YOU, then this is called an autoimmune reaction.

IgM

first antibody produced by activated B cells. Future activations will cause these cells to produce a different class of antibody with a constant region that is most appropriate for where that antibody will act in the body. *Its really large! Maybe gives more "bang binding" for its buck in the initial crisis of infection. (I found out that the "M" is for MACRO because these things are so big relative to other antibodies) *Its most well-known for being produced by plasma cells within the spleen.

IgA

my favorite class of antibody. :-) *This is by far the most common antibody on your mucous membranes and in body secretions. *plentiful in breast milk to protect babies from respiratory and GI infections and probably even skin infections. *Neisseria and a few other bacteria have a virulence factor of making an enzyme that destroys IgA! Smart! *celiac disease is one example of an autoimmune disease in which there is an inappropriate IgA response to gluten.

variable region of an antibody

the region of an antibody that binds antigen

What is a "class switch" for antibodies?

After a B cell has responded to a pathogen's antigen with the generic IgM, future activations will cause the antibodies to "switch" their constant region for better efficiency in a particular environment (blood, mucous membranes, etc.).

B cell

B cells are lymphocytes of the adaptive immune system. When they are activated, they develop into plasma cells and begin producing vast quantities of antibodies.

Which type of antibody is ALWAYS produced during the primary exposure (the first time any B cell recognizes a pathogen's antigen)?

IgM High levels in the blood may indicate an active infection.

How do antibodies function?

*Antibodies do not kill pathogens; instead they mark pathogens for destruction by Cyotoxic T cells or phagocytosis by macrophages. *Macrophages favorite food is "antibody-encrusted pathogen". :-) They can "smell" them like a shark smells blood in the water. *The binding of antibodies to a pathogen can prevent it from binding to our body membranes *The binding of antibodies to an antigen can activate complement and its "membrane attack complex" *In some cases, the antibodies bind to the TOXIN produced by the pathogen (rather than the pathogen itself). Examples of this include Diphtheriae and Tetanus toxins (rather than Corynebacterium and Clostridium cells)

IgE

*most associated with allergies and autoimmunities! *IgE will bind to mast cells and basophils and overstimulate histamine release when they are also bound to their antigen. *primary function has probably been to fight off eukaryotic infections, particularly parasitic worms. Not surprisingly, many parasitic worms try to combat this by releasing "calming signals" that reduce this IgE inflammatory response. *apparently the least common class of antibody; nevertheless, its powerful ability to stimulate mast cells can make it elicit the most potent inflammatory response. *remember, the plasma cells originally produced IgM, and then the subsequent antibodies undergo a class switch to this IgE class type.

What are the parts of an antibody?

*variable regions are the "arms" of the antibody that bind to the pathogen's matching antigen *constant region is the part of the antibody that is specialized for living in different parts of the body - blood, mucous membranes, etc.