Webster's New World Medical Dictionary

histiocytosis, Langerhans cell
See 
Langer-
hans cell histiocytosis.
histiocytosis, lipid
See 
Niemann-Pick disease.
histiocytosis, sinus
A type of histiocytosis in
which the lymph nodes are the main site of histio-
cyte proliferation. The sinuses of the lymph nodes
become filled with and distended by masses of 
histiocytes.
histiocytosis X
See 
Langerhans cell histiocytosis.
histocompatible
Literally, tissue compatible,
meaning that the tissue can exist together with tissue
of another organism without the immune system
rejecting it. If a tissue donor and tissue recipient are
histocompatible, a transplant is expected to be eas-
ily accepted.
histology
The study of tissues as seen under a
microscope. Also known as microscopic anatomy,
as opposed to gross anatomy.
histone
A protein around which DNA coils to
form chromatin. Without histones, DNA could not
organize into chromosomes.
Histoplasma capsulatum
A fungus that is found
worldwide that is particularly common in the cen-
tral and eastern parts of the US. It is carried in bird
and bat droppings, and it is deposited in the soil.
Although people can contract histoplasma from
their environment, it cannot be passed from person
to person. While most persons exposed to H. cap-
sulatum do not become ill, some people develop a
disease that predominantly affects the lungs called
histoplasmosis. See also 
histoplasmosis.
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histoplasmosis
A disease caused by the fungus
Histoplasma capsulatum. Most people with histo-
plasmosis have no symptoms. However, it can cause
acute or chronic lung disease and progressive dis-
seminated histoplasmosis, which affects a number
of organs. Infants, young children, and older per-
sons—particularly those with chronic lung dis-
ease—are at increased risk for severe disease.
Disseminated histoplasmosis is most frequently
seen in people with cancer or AIDS. The acute res-
piratory disease of histoplasmosis is characterized
by respiratory symptoms, a general ill feeling, fever,
chest pains, and a dry or nonproductive cough.
Distinct patterns may be seen on a chest x-ray.
Chronic lung disease related to histoplasmosis
resembles tuberculosis and can worsen over
months or years. The disseminated form is fatal
unless treated. Mild cases resolve without treatment.
Severe cases of acute histoplasmosis and all cases of
chronic and disseminated histoplasmosis are
treated with antifungal medications, usually for life
in those with compromised immune systems.