|
Explanation
of antigens and antibodies for parents adopting from Asia.
The first picture (left) shows four hepatitis B viruses
or "Dane particles", consisting of an envelope andan
inner capsid with DNA. Phosphotungstate staining; magnification
of the original is 297,000 times. The second picture (right) is
at much lower magnification and displays spherical and tubular
HBsAg ("Australia antigen") particles, stained with
uranyl acetate.
The virus of type B hepatitis (hepadnavirus) is specific for humans
and its target is the human liver. The virus causes inapparent,
acute and various types of chronic infections. As every virus
(or bacterium), the B virus consists of several antigens, each
of which stimulate the human organism to produce specific antibodies.
An antigen is a molecule of carbohydrate or protein. An
antibody is a protein produced by humans or other vertebrates
in response to a foreign antigen. Its role is essentially protective.
The presence of virus antigens in the blood proves the presence
of the particular infecting virus. The presence, in the blood,
of antibodies against this virus (or its antigens) proves that
the virus is or has been present. It may indicate that the individual
is immunized (protected) after a natural infection or a vaccination.
In hepatitis B infections, the most important antigens are the
core (c) antigen and the surface (s) antigen. The
full name of the latter is HBsAg. They give rise to antibodies
named anti-c and anti-s, respectively, which appear after the
c and s antigens. Antigen and antibody levels are determined by
radioimmunoassay or enzymatic (ELISA) tests.
Acute infections and chronic infections are accompanied by modifications
of liver function, wich are detectable biochemically and and can
be used to predict the outcome of the disease. The most important
tests are determination of transaminases (ALT and AST) and bilirubin.
The presence of anti-s and anti-c antibodies in HBsAg-negative
persons, together with normal biochemical tests, indicates healing
and immunity. B hepatitis has become chronic if HbsAg persists
for than six months, transaminase and bilirubin levels remain
elevated and the prothrombin-time (a blood coagulation test) is
abnormally long. Chronic hepatitis may be "persistent"
or relatively benign, or "active" and malign with a
tendency to progress to cirrhosis. In developing countries, 70-100%
of adults show evidence of past hepatitis B infection (presence
of anti-s). Prevalence is particularly high in China and South-East
Asia. In these countries, infections are generally perinatal,
that is around the time of birth (not before because the virus
does usually not cross the placenta)..
|
