Antibody -- Any of the protein molecules produced by specialized immune system cells (B cells) that can recognize and bind to a particular foreign antigen. If the antigen is on the surface of a cell, this binding leads to cell aggregation and subsequent destruction. Antibodies are also referred to as immunoglobulins.

Antigens -- A substance that induces the formation of antibodies because the immune system recognizes it as a threat. It may be a foreign substance from the environment, such as chemicals, or formed within the body, such as bacterial or viral toxins.

Complement -- The thermolabile group of proteins in normal blood serum and plasma that in combination with antibodies causes the destruction especially of particulate antigens (as bacteria and foreign blood corpuscles).

Escherichia coli, or E. coli -- A common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of culture in the laboratory.

Immunochemistry -- The branch of medical science that studies the body's immune system; the chemistry of immunologic phenomena.

Immunology -- The branch of biomedicine concerned with the structure and function of the immune system, innate and acquired immunity, the bodily distinction of self from nonself, and laboratory techniques involving the interaction of antigens with specific antibodies.

Klebsiella -- A genus of gram-negative, facultatively anaerobic, rod-shaped bacteria whose organisms arrange singly, in pairs, or short chains. This genus is commonly found in the intestinal tract and is an opportunistic pathogen that can give rise to bacteremia, pneumonia, urinary tract, and several other types of human infection.

Pneumococcus -- A nonmotile bacterium (Streptococcus pneumoniae) that is the most common cause of bacterial pneumonia. It is often associated with meningitis and other infectious diseases.

Pneumonia -- An acute or chronic disease marked by inflammation of the lungs and caused by viruses, bacteria, and/or other microorganisms or physical and chemical irritants.

Polysaccharide -- A carbohydrate that can be decomposed by hydrolysis into two or more molecules, especially one (as cellulose, starch) containing many monosaccharide units marked by complexity.

Preciptin -- An antibody that when combined with soluble antigens creates visible precipitations of large antibody-antigen complexes.