Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Hydrophobic and hydrophilic

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HUMANT-CELL LEUKEMIA VIRUS

(HTLV)Human T-cell leukemia virus (HTLV)

Two types of human T-cell Leukemia Virus (HTLV) are

known. They are also known as human T-cell lymphotrophic

viruses. HTLV-1 often is carried by a person with no overt

symptoms being apparent. However, HTLV-I is capable of

causing a number of maladies. These include abnormalities of

the T cellsand B cells, a chronic infection of the myelin cov-

ering of nerves that causes a degeneration of the nervous sys-

tem, sores on the skin, and an inflammationof the inside of the

eye. HTLV-II infection usually does not produce any symp-

toms. However, in some people a cancer of the blood known

as hairy cell leukemia can develop.

At one time there was a third HTLV virus. However,

what once called HTLV-III is now referred to as the Human

Immunodeficiency Virus(HIV). HIV is generally accepted to be

the causative agent of acquired immunodeficiencysyndrome.

HTLV is a type of virus called a retrovirus. These

viruses are unique in that they possess an enzyme that enables

them to manufacture deoxyribonucleic acidfrom their con-

stituent ribonucleic acid.

HTLV-I is most commonly associated with a disease

called adult T-cell leukemia, which is a rapidly spreading can-

cerous growth that affects the T cells of the immune system.

Indeed, the virus was first isolated in 1980 from a patient with

T-cell lymphoma. Once the symptoms of the disease appear,

deterioration of the individual occurs quickly. However, the

symptoms may not appear for decades after the virus has

infected someone. The reason for this extended period of

latency is not known. HTLV-I has also been isolated from peo-

ple who have maladies that include arthritis, Kaposi’s sar-

coma, and non-Hodgkin’s lymphoma. Whether the virus is a

contributor to such maladies, or is coincidentally expressed, is

not yet clear.

The HTLV-I form of the virus is found all over the

world. However, it is more prevalent in some countries, such

as Japan, than in other countries, such as the United States.

HTLV-II was isolated in 1982 from a patient with hairy

cell leukemia. Even so, the virus still has not been definitively

established as the cause of that malady. However, the frequent

isolation of HTLV-II from patients with this form of leukemia,

as well as other types of leukemia’s and lymphomas, lends

credence to the theory that the virus is vital for the develop-

ment of the malignancies.

HTLV-II is found in many intravenous drug users.

Transmission of the virus from person to person via the con-

taminated blood in the needles used for drug injection has

been documented. HTLV-II can also be spread by exchange of

other body fluids, such as occurs in sexual contact.

In spite of the above conditions associated with HTLV-

II, the majority of those infected with the virus do not display

any symptoms.

The virus can be passed from person to person by the

transfer of contaminated blood or via the intimate association

of sexual contact. Also, the virus is capable of being passed

from mother to infant via breast milk. Blood donor programs

in many countries now rigorously test for the presence of

HTLV in donated blood and plasma.

HTLV infections are incurable. However, the progres-

sive physical deterioration associated with the infections can

be lessened somewhat if the infections are diagnosed early.

Screening for the virus relies on the detection of antibodies.

Typically, antigen-antibody agglutination tests or the enzyme-

linked immunosorbent assay(ELISA) is used. Confirmation of

infections is provided by demonstrating the presence of viral

protein in electrophoretic gels following the application of an

antibody(the technique is dubbed the Western Blot).

See alsoAIDS; Immunodeficiency

HUMORAL IMMUNE RESPONSE•see

IMMUNITY, HUMORAL REGULATION

HHydrophobic and hydrophilicYDROPHOBIC AND HYDROPHILIC

Hydrophobic and hydrophilic forces are interactions that serve

to keep chemical groups positioned close to one another. Such

associations are vital for the structure of the components of

microorganisms.

Hydrophobic (“water hating”) interactions are created

because of the uncharged nature of the involved chemical

groups. An example of such a chemical group is CH 3. All the

bonds around the carbon atom are occupied. The chemical

group is described as being nonpolar. Thus, a water mole-

cule—a polar molecule—is unable to establish an association

with the non-polar chemical group. This tends to create insta-

bility in the network of water molecules, and so is undesirable.

The repulsive force of the surrounding water molecules acts to

force hydrophobic regions into an association with like

regions. The effect tends to be the formation of a hydrophobic

“pocket” or “envelope” in a protein or a carbohydrate mole-

cule or matrix.

Hydrophilic (“water loving) interactions are possible

with polar chemical group. Water is polar because oxygen is

far more electronegative than hydrogen and thus the electrons

involved in an oxygen-hydrogen bond spend more time in

proximity to the oxygen atom. Because of this unequal elec-

tron sharing, the oxygen atom takes on a partial negative

charge and the hydrogen atom a partial positive charge. In

addition, the bonds in a water molecule (oriented at 105° in a

“bent” molecular shape) cannot cancel each other out. Other

polar groups can then form ionic type bonds with water.

Regions of proteins and other biological materials that are

exposed to the environment are typically hydrophilic.

Hydrophobic and hydrophilic interactions can affect

protein shape. Because of the polar or nonpolar nature of the

constituent amino acid building blocks, as well as in carbo-

hydrate and lipid constituents of microorganisms, molecules

and sometimes whole microorganisms can assume shapes

and orientations that depend on the intracellular or extracel-

lular environment.

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