which contains mercury. Because this heavy metal
can cause neurologic damage, the United States
has initiated a cooperative effort among vaccine
manufacturers to develop thimerosal-free vac-
cines. Most recommended vaccines are now avail-
able without thimerosal or with minimal amounts
of thimerosal.
People who travel should receive vaccines
appropriate for the regions they intend to visit.
The US Centers for Disease Control and Preven-
tion (CDC) maintains a schedule of recommended
travelers’ immunizations at its Web site
(http://www.cdc.gov).
See also ANTIBODY; ANTITOXIN; ANTIVENIN; B-CELL
LYMPHOCYTE; CHILDHOOD DISEASES; INFLUENZA PREVEN-
TION; LYMPHOCYTE; PREVENTIVE HEALTH CARE AND IMMU-
NIZATIONS.
vascular-associated lymphoid tissue (VALT)
Loosely collected clusters of LY M P Htissue through-
out the inner, mucosal layer of the walls of the
BLOODvessels. Researchers discovered VALT in the
late 1990s and remain unsure of its role and func-
tions. There do appear to be correlations between
LYMPHOCYTE activity in VALT and cardiovascular
conditions such as ATHEROSCLEROSIS, which many
cardiologists now believe results from an inflam-
matory process rather than creates INFLAMMATION.
Researchers do not know, however, whether VALT
attempts to fight the inflammation or contributes
to it. Researchers are also investigating the rela-
tionship between VALT and dissecting aortic
ANEURYSM, a life-threatening condition in which
the layers of the walls of the abdominal AORTA
begin to separate. The separations weaken the
wall of this major ARTERY, creating substantial risk
for the arterial wall to rupture.
For further discussion of VALT within the con-
text of the structures and functions of the immune
system, please see the overview section “The
Immune System and Allergies.”
See also BRONCHIAL-ASSOCIATED LYMPHOID TISSUE
(BALT); GUT-ASSOCIATED LYMPHOID TISSUE (GALT);
MUCOSA-ASSOCIATED LYMPHOID TISSUE (MALT); NOSE-
ASSOCIATED LYMPHOID TISSUE(NALT); SKIN-ASSOCIATED
LYMPHOID TISSUE(SALT); VASCULITIS.vasculitis A group of AUTOIMMUNE DISORDERS in
which the epithelium (lining) of the BLOODvessels
becomes inflamed. The INFLAMMATIONcauses local-
ized PAINand swelling. There are numerous forms
of vasculitis. They share common characteristicsvasculitis 299TYPES OF VASCULITISType of Vasculitis Unique Symptoms Treatment and Outlook
allergic granulomatosis and primarily occurs in adults who have CORTICOSTEROID MEDICATIONS
angiitis (Churg-Strauss atopic bronchial ASTHMA sometimes resolves spontaneously though often
syndrome) affects BLOODvessels of the LUNGSand is chronic
musculoskeletal system course of disease may be progressive
eosinophilia (excessive number of untreated eosinophilic pneumonia is life
eosinophils) and eosinophilic PNEUMONIA threatening
Behçet’s syndrome primarily occurs in adults who are in topical corticosteroid medications for mild
their 30s and is more common in men skin symptoms
affects small arteries and veins serving colchicine,NONSTEROIDAL ANTI-INFLAMMATORY DRUGS
epithelial tissue (SKINand mucous (NSAIDS), dapsone, or thalidomide to control
membranes) and the eyes ulcerations
recurrent, painful ulcers in the MOUTH IMMUNOSUPPRESSIVE MEDICATIONSfor severe symptoms
and VULVAthat occur in clusters that do not respond to other treatments
vision disturbances and UVEITIS tends to be chronic with extended periods of
inflammatory response with minor trauma REMISSION(several years)
such as scratches PHYSICAL THERAPYand physical exercise as tolerated
skin rashes to maintain joint FLEXIBILITYand range of motion