Microbiology and Immunology

Glycocalyx WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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Alpha and beta globulins function as enzymesand pro-

teins that transport compounds in the body. Gamma globulins

act as the antibodydefense against antigen invasion.

Beta globulins are also manufactured predominantly in

the liver. Akin to the alpha type globulins, there are beta-1 and

beta-2 globulins. Examples of beta globulins include a protein

that binds iron in the body, factors involved with the immune

targeting of foreign material for immune destruction, and a

species of immunoglobulin antibody termed IgM.

Gamma globulins are manufactured in cells of the

immune system known as lymphocytes and plasma cells.

These globulins, which are known as IgM, IgA, and IgG, rep-

resent antibodies. Depending on the nature of the invading

antigen, a specific immun globulin will be produced in great

numbers by a specific lymphocyte or plasma cell. Infection

with a different antigen will stimulate the production of a dif-

ferent immune globulin. As the infection eases, the production

of the immun globulin will decrease.

The quantities of the various globulins in the blood can

be diagnostic of malfunctions in the body or specific diseases.

Examples of maladies that affect the globulin levels are

chronic microbial infections, liver disease, autoimmune disor-

ders, leukemias, and rheumatoid arthritis.

See alsoImmunity: active, passive, and delayed; Immunity,

cell mediated; Immunity, humoral regulation; Immuno-

chemistry; Immunogenetics; Immunoglobulins and immuno-

globulin deficiency syndromes; Immunologic therapies;

Immunological analysis techniques; Laboratory techniques in

immunology

GGlycocalyxLYCOCALYX

The glycocalyx is a carbohydrate-enriched coating that covers

the outside of many eukaryotic cells and prokaryotic cells,

particularly bacteria. When on eukaryotic cells the glycocalyx

can be a factor used for the recognition of the cell. On bacte-

rial cells, the glycocalyx provides a protective coat from host

factors. The possession of a glycocalyx on bacteria is associ-

ated with the ability of the bacteria to establish an infection.

The glycocalyx of bacteria can assume several forms. If

in a condensed form that is relatively tightly associated with

the underlying cell wall, the glycocalyx is referred to as a cap-

sule. A more loosely attached glycocalyx that can be removed

from the cell more easily is referred to as a slime layer.

The bacterial glycocalyx can vary in structure from bac-

teria to bacteria. Even particular bacteria can be capable of

producing a glycocalyx of varying structure, depending upon

the growth conditions and nutrients available. Generally, the

glycocalyx is constructed of one or more sugars that are called

saccharides. If more than one saccharide is present, the glyco-

calyx is described as being made of polysaccharide. In some

glycocalyces, protein can also be present.

There are two prominent functions of the glycocalyx.

The first function is to enable bacteria to become harder for the

immune cells called phagocytes so surround and engulf. This is

because the presence of a glycocalyx increases the effective

diameter of a bacterium and also covers up components of the

bacterium that the immune systemwould detect and be stimu-

lated by. Thus, in a sense, a bacterium with a glycocalyx

becomes more invisible to the immune system of a host.

Infectious strains of bacteria such as Staphylococcus,

Streptococcus,and Pseudomonastend to elaborate more gly-

cocalyx than their corresponding non-infectious counterparts.

The second function of a bacterial glycocalyx is to pro-

mote the adhesion of the bacteria to living and inert surfaces

and the subsequent formation of adherent, glycocalyx-enclosed

populations that are called biofilms. Biofilm bacteria can

become very hard to kill, party due to the presence of the gly-

cocalyx material. Many persistent infections in the body are

caused by bacterial biofilms. One example is the dental plaque

formed by glycocalyx-producing Streptococcus mutans, which

can become a focus for tooth enamel-digesting acid formed by

the bacteria. Another example is the chronic lung infections

formed in those afflicted with certain forms of cystic fibrosis

by glycocalyx-producing Pseudomonas aeruginosa. The latter

infections can cause sufficient lung damage to prove lethal.

See alsoAnti-adhesion methods; Bacterial surface layers

GGolgi, Camillo OLGI, CAMILLO(1843-1926)

Italian histologist

Among other achievements in neurobiology, Camillo Golgi

devised a method of staining nerve tissue using silver nitrate.

Golgi-stained nerve tissue revealed unique structures with

fine projections, which were later recognized as individual

cells, or neurons.

Golgi was born in Corteno, Italy, on July 7, 1843. His

hometown was later re-named Corteno-Golgi in his honor.

Golgi studied medicine at the University of Pavia, where he

received his M.D. in 1865. After graduation, he worked briefly

in a psychiatric clinic, but eventually decided to pursue a

career in histological research.

Financial difficulties forced him in 1872 to accept a

position as chief medical officer at the Hospital for the

Chronically Ill in Abbiategrasso, Italy. No research facilities

were available there, however, and he was able to continue his

studies only by converting an unused kitchen into a laboratory.

By 1875, Golgi had earned sufficient fame to receive an

appointment as lecturer in histology at the University of Pavia.

Four years later, he was appointed Professor of Anatomy at the

University of Siena, but he stayed only a year there before

returning to Pavia as Professor of Histology.

Golgi’s earliest research involved the study of neurons, or

nerve cells. Neurons present a number of problems for

researchers that other cells do not. While most cells are compact

and have a relatively fixed shape, neurons are commonly very

long and thin with structures that are difficult to see clearly. In

the 1860s, techniques used to stain and study non-nerve cells

were well developed, but they were largely useless with neu-

rons. As a result, a great deal of uncertainty surrounded the

structure and function of neurons and neuron networks.

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