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H chain disease 308 halothane antigens
any one molecule, as are the two light chains. Refer also to
heavy chain.
H chain disease
A variant of multiple myeloma in which immunoglobulin
free heavy chains are demonstrable in serum. This condition,
characterized by free H chains in the serum but not
free light chains, is called heavy chain disease.
H substance
A basic carbohydrate of the human ABO blood group
system structure. Most people express this ABO-related
antigen. The body fluids of secretor individuals contain
soluble H substance.
H 1, H 2 blocking agents
Refer to antihistamine.
H1 receptors
Histamine receptors on vascular smooth muscle cells
through which histamine mediates vasodilation.
H2 receptors
Histamine receptors on different types of tissue cells
through which histamine mediates bronchial constriction
in asthma, gastrointestinal constriction in diarrhea, and
endothelial constriction resulting in edema.
HA-1A
Human monoclonal immunoglobulin M (IgM) antibody
specific for the lipid A domain of endotoxin. It can prevent
deaths of laboratory animals that have Gram-negative bacteremia
and endotoxemia. In clinical trials, HA-1A has proven
safe and effective for the treatment of patients with sepsis and
Gram-negative bacteremia, whether or not they are in shock,
but not in those with focal Gram-negative infections.
HAART
A regimen comprised of at least two different types of antiretroviral
drugs as a cocktail to treat HIV-infected patients.
Refer to highly active antiretroviral therapy.
haemolin
A protein that occurs in soluble form in hemolymph and as a
membrane-bound protein on phagocytic hemocyte surfaces.
Soluble haemolin serves as an opsonin on whole pathogens
or lipopolysaccharide (LPS) and facilitates phagocytosis.
Haemophilus b conjugate vaccine (injection)
Induces protective antibody to Haemophilus b polysaccharide.
A preexisting titer of antibody to HbPs of 0.15 mcg/mL
correlates with protection. Data from a Finnish field trial in
children 18 to 71 months of age suggests that a titer of >1 μg/
mL 3 weeks after vaccination is linked to long-term protection.
Linkage of Haemophilus b saccharides to a protein such
as CRM 197 converts the saccharide (HbO) to a T-dependent
(HbOC) antigen and leads to enhanced antibody response
to the saccharide in infants that primes for an anamnestic
response and is mainly IgG. The response to ActHIB is
a classic T-dependent immune response. IgG is the main
isotype of anticapsular PRP antibody induced by ActHIB.
A prominent booster response has been shown in children
12 months of age or older who previously received two or
three doses. Bactericidal activity against H. influenzae type
b is present in serum after immunization and correlates
statistically with the anti-PRP antibody response induced by
ActHIB. Antibody to H. influenzae capsular polysaccharide
(anti-PRP) titers of >1 μg/mL after vaccination with unconjugated
PRP vaccine correlated with long-term protection
against invasive H. influenzae type b disease in children
older than 24 months of age. ActHIB induced anti-PRP levels
greater than or equal to 1 μg/mL in 90% of infants after the
primary series and in 98% of infants after a booster dose.
Haemophilus immunity
Serum bactericidal activity to Haemophilus influenzae
serotype b (Hib) is associated with protection from infection.
This effect is mediated by antibody to the capsule.
Antibody to the PRP polysaccharide capsule protects
against invasive infection. Two-year-olds have only low
titers of anticapsular antibodies and are susceptible to reinfection
and episodes of Hib meningitis. NTHI strains of the
organism demonstrate antigenic heterogeneity of surface
antigens among strains. Infection does not induce protective
immunity from infection by NTHI strains following otitis
media attributable to an NTHI strain. Serum bactericidal
antibody associated with protection develops. The immune
response is strain-specific, rendering the child susceptible to
infection with other strains of NTHI. The immune response
is strain-specific with reactivity directed to the immunodominant
surface epitopes on the P2 OMP. H. influenzae
LOS is a principal toxin against which humoral immune
responses are directed. The mucosal immune response to
NTHI remains to be defined. Conjugate vaccines developed
to prevent invasive infections by Hib have been very
successful in preventing the infectious disease. High titers
of serum IgG specific for Hib capsular polysaccharide are
associated with increased bactericidal and protective activity.
Linking the PRP capsular polysaccharide to protein
carriers has yielded a conjugate vaccine that is effective in
protecting infants against invasive Hib infections.
Haemophilus influenzae type b vaccine (HB)
An immunizing preparation that contains purified polysaccharide
antigen from H. influenzae microorganisms and a carrier
protein. It diminishes the risks of epiglottitis, meningitis,
and other diseases induced by H. influenzae during childhood.
Hageman factor (HF)
A zymogen in plasma that is activated by contact with a
surface or by the kallikrein system at the beginning of the
intrinsic pathway of blood coagulation. This is an 80-kDa
plasma glycoprotein which, following activation, is split
into α and β chains. When activated, it is a serine protease
that transforms prekallikrein into kallikrein. HF is coagulation
factor XII.
hairpin loop
The looped structure of hairpin DNA.
hairy cell leukemia
A B lymphocyte leukemia in which the B cells have characteristic
cytoplasmic filopodia.
half-life (T 1/2)
The time required for a substance to be diminished to one
half of its earlier level by degradation or decay; by catabolism,
as in biological half-life; or by elimination. In immunology,
T 1/2 refers to the time in which an immunoglobulin
remains in the blood circulation. For IgG, the half-life is 20
to 25 days; for IgA, 6 days; for IgM, 5 days; for IgD, 2 to 8
days; and for IgE, 1 to 5 days.
halogenation
Halogen binding to the cell wall of a microorganism with
resulting injury to the microbe.
halothane antigens
Antigenic determinants that result from the action of halothane
on rabbit and rat liver cell components. Also referred
to as TFA antigens.